bug: output guardrail error message echoes the matched forbidden literal back to caller #153

Closed
#203
Closed
bug: output guardrail error message echoes the matched forbidden literal back to caller#153
#203
Labels
bugSomething isn't workingpriority-normalvulnerability

Description

@moonming
moonming
opened on May 9, 2026

Summary

When an output guardrail with kind: "keyword" and hook_point: "output" blocks an upstream response containing a forbidden literal, the gateway's caller-visible error message includes the matched literal verbatim — defeating the purpose of an output guardrail (which exists precisely to keep forbidden content from reaching the caller).

Repro

E2E test attached: drafted as tests/e2e/src/cases/guardrail-output-e2e.test.ts (held back from #151 batch 2 PR pending this fix).

Setup:

  • Mock upstream returns assistant message containing the literal "leakedsecret"
  • Output keyword guardrail configured with patterns: [{kind:"literal", value:"leakedsecret"}]
  • Caller sends an innocent prompt

Observed:
```json
{
"error": {
"message": "content blocked by policy: output blocked by literal "leakedsecret"",
"type": "content_filter"
}
}
```

The forbidden literal is right there in error.message. Anyone who can trigger the guardrail can extract the policy's blocklist by inspecting error responses.

Expected:
```json
{
"error": {
"message": "response blocked by content policy",
"type": "content_filter"
}
}
```

Or any redacted equivalent that does NOT include the matched pattern.

Severity

MEDIUM-HIGH for output guardrails specifically:

  • For input guardrails, leaking the matched pattern back is mostly cosmetic — the caller sent it, they already know.
  • For output guardrails, leaking the matched pattern is a real information leak — the whole point is to prevent the model's forbidden output from reaching the caller. Echoing it in the error envelope is a partial bypass.

Proposed fix

Strip / redact the matched value from the error rendered to clients. Internal logs may keep the matched pattern for operator debugging, but the wire-level error.message and any other caller-visible field must not carry it.

Test attached

The held-back test asserts:
```ts
const errorBlob = JSON.stringify(caught.error ?? {});
expect(errorBlob).not.toContain(FORBIDDEN_WORD);
```

Will be added back to the e2e suite once this is fixed.

Metadata

Metadata

Assignees

No one assigned

    Labels

    bugSomething isn't workingpriority-normalvulnerability

    Type

    No type

    Projects

    No projects

      Milestone

      No milestone

      Relationships

      None yet

      Development

      No branches or pull requests

      Issue actions

      , 'i'); if (__m === '*' || __re.test(location.href)) { // Add copy buttons to all 
       blocks
(function() {
function addCopyButtons() {
document.querySelectorAll('pre code').forEach(function(codeBlock) {
if (codeBlock.parentElement.hasAttribute('data-copy-added')) return;
codeBlock.parentElement.setAttribute('data-copy-added', 'true');
var btn = document.createElement('button');
btn.textContent = 'Copy';
btn.style.cssText = 'position:absolute;top:4px;right:4px;padding:2px 8px;font-size:11px;background:#4ecdc4;border:none;border-radius:4px;color:#1a1a2e;cursor:pointer;opacity:0.7;transition:opacity 0.2s;';
btn.onmouseover = function() { this.style.opacity = '1'; };
btn.onmouseout = function() { this.style.opacity = '0.7'; };
btn.onclick = function() {
navigator.clipboard.writeText(codeBlock.textContent).then(function() {
btn.textContent = 'Copied!';
setTimeout(function() { btn.textContent = 'Copy'; }, 1500);
});
};
codeBlock.parentElement.style.position = 'relative';
codeBlock.parentElement.appendChild(btn);
});
}
addCopyButtons();
// Re-run on dynamic content
var observer = new MutationObserver(addCopyButtons);
observer.observe(document.body, { childList: true, subtree: true });
})();
}
} catch(__e) { console.warn('[Userscript:Add Copy Buttons to Code Blocks]', __e); }
})();
(function(){
try {
var __m = "github.com";
var __re = new RegExp('^' + "github\\.com" + '

      Skip to content
      bug: output guardrail error message echoes the matched forbidden literal back to caller #153
      Closed
      #203
      Closed
      bug: output guardrail error message echoes the matched forbidden literal back to caller#153
      #203
      Labels
      bugSomething isn't workingpriority-normalvulnerability
      Description
      @moonming
      moonming
      opened on May 9, 2026
      Summary
      When an output guardrail with kind: "keyword" and hook_point: "output" blocks an upstream response containing a forbidden literal, the gateway's caller-visible error message includes the matched literal verbatim — defeating the purpose of an output guardrail (which exists precisely to keep forbidden content from reaching the caller).
      Repro
      E2E test attached: drafted as tests/e2e/src/cases/guardrail-output-e2e.test.ts (held back from #151 batch 2 PR pending this fix).
      Setup:
      • Mock upstream returns assistant message containing the literal "leakedsecret"
      • Output keyword guardrail configured with patterns: [{kind:"literal", value:"leakedsecret"}]
      • Caller sends an innocent prompt
      Observed:
      
```json
      
{
      
"error": {
      
"message": "content blocked by policy: output blocked by literal "leakedsecret"",
      
"type": "content_filter"
      
}
      
}
      
```
      The forbidden literal is right there in error.message. Anyone who can trigger the guardrail can extract the policy's blocklist by inspecting error responses.
      Expected:
      
```json
      
{
      
"error": {
      
"message": "response blocked by content policy",
      
"type": "content_filter"
      
}
      
}
      
```
      Or any redacted equivalent that does NOT include the matched pattern.
      Severity
      MEDIUM-HIGH for output guardrails specifically:
      • For input guardrails, leaking the matched pattern back is mostly cosmetic — the caller sent it, they already know.
      • For output guardrails, leaking the matched pattern is a real information leak — the whole point is to prevent the model's forbidden output from reaching the caller. Echoing it in the error envelope is a partial bypass.
      Proposed fix
      Strip / redact the matched value from the error rendered to clients. Internal logs may keep the matched pattern for operator debugging, but the wire-level error.message and any other caller-visible field must not carry it.
      Test attached
      The held-back test asserts:
      
```ts
      
const errorBlob = JSON.stringify(caught.error ?? {});
      
expect(errorBlob).not.toContain(FORBIDDEN_WORD);
      
```
      Will be added back to the e2e suite once this is fixed.
      Metadata
      Metadata
      Assignees
      No one assigned
        Labels
        bugSomething isn't workingpriority-normalvulnerability
        Type
        No type
        Projects
        No projects
          Milestone
          No milestone
          Relationships
          None yet
          Development
          No branches or pull requests
          Issue actions
          
, 'i');
if (__m === '*' || __re.test(location.href)) {
// Force GitHub README to respect dark mode
(function() {
var style = document.createElement('style');
style.textContent = '
.markdown-body {
color-scheme: dark light;
}
.markdown-body pre { background: #161b22 !important; }
.markdown-body code { background: rgba(110, 118, 129, 0.4) !important; }
.markdown-body table th, .markdown-body table td { border-color: #30363d !important; }
.markdown-body img { background: #0d1117; }
.markdown-body blockquote { border-left-color: #8b949e; }
.markdown-body hr { border-color: #30363d; }
';
document.head.appendChild(style);
})();
}
} catch(__e) { console.warn('[Userscript:GitHub Dark Mode README Fix]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

          Skip to content
          bug: output guardrail error message echoes the matched forbidden literal back to caller #153
          Closed
          #203
          Closed
          bug: output guardrail error message echoes the matched forbidden literal back to caller#153
          #203
          Labels
          bugSomething isn't workingpriority-normalvulnerability
          Description
          @moonming
          moonming
          opened on May 9, 2026
          Summary
          When an output guardrail with kind: "keyword" and hook_point: "output" blocks an upstream response containing a forbidden literal, the gateway's caller-visible error message includes the matched literal verbatim — defeating the purpose of an output guardrail (which exists precisely to keep forbidden content from reaching the caller).
          Repro
          E2E test attached: drafted as tests/e2e/src/cases/guardrail-output-e2e.test.ts (held back from #151 batch 2 PR pending this fix).
          Setup:
          • Mock upstream returns assistant message containing the literal "leakedsecret"
          • Output keyword guardrail configured with patterns: [{kind:"literal", value:"leakedsecret"}]
          • Caller sends an innocent prompt
          Observed:
          
```json
          
{
          
"error": {
          
"message": "content blocked by policy: output blocked by literal "leakedsecret"",
          
"type": "content_filter"
          
}
          
}
          
```
          The forbidden literal is right there in error.message. Anyone who can trigger the guardrail can extract the policy's blocklist by inspecting error responses.
          Expected:
          
```json
          
{
          
"error": {
          
"message": "response blocked by content policy",
          
"type": "content_filter"
          
}
          
}
          
```
          Or any redacted equivalent that does NOT include the matched pattern.
          Severity
          MEDIUM-HIGH for output guardrails specifically:
          • For input guardrails, leaking the matched pattern back is mostly cosmetic — the caller sent it, they already know.
          • For output guardrails, leaking the matched pattern is a real information leak — the whole point is to prevent the model's forbidden output from reaching the caller. Echoing it in the error envelope is a partial bypass.
          Proposed fix
          Strip / redact the matched value from the error rendered to clients. Internal logs may keep the matched pattern for operator debugging, but the wire-level error.message and any other caller-visible field must not carry it.
          Test attached
          The held-back test asserts:
          
```ts
          
const errorBlob = JSON.stringify(caught.error ?? {});
          
expect(errorBlob).not.toContain(FORBIDDEN_WORD);
          
```
          Will be added back to the e2e suite once this is fixed.
          Metadata
          Metadata
          Assignees
          No one assigned
            Labels
            bugSomething isn't workingpriority-normalvulnerability
            Type
            No type
            Projects
            No projects
              Milestone
              No milestone
              Relationships
              None yet
              Development
              No branches or pull requests
              Issue actions
              
, 'i');
if (__m === '*' || __re.test(location.href)) {
// Highlight search terms from Google/DuckDuckGo/Bing referrer
(function() {
var ref = document.referrer;
var terms = [];
if (ref.includes('google.com') || ref.includes('duckduckgo.com') || ref.includes('bing.com')) {
var url = new URL(ref);
var q = url.searchParams.get('q') || url.searchParams.get('p');
if (q) {
terms = q.split(/\s+/).filter(function(t) { return t.length > 2; });
}
}
if (terms.length === 0) return;
var style = document.createElement('style');
style.textContent = '.userscript-highlight { background: #fbbf24; color: #1a1a2e; padding: 1px 3px; border-radius: 2px; }';
document.head.appendChild(style);
function highlight(node) {
if (node.nodeType === 3) { // text node
var text = node.textContent;
var found = false;
terms.forEach(function(term) {
var regex = new RegExp('(' + term.replace(/[.*+?^${}()|[\]\\]/g, '\\') + ')', 'gi');
if (regex.test(text)) {
found = true;
var frag = document.createDocumentFragment();
var parts = text.split(regex);
parts.forEach(function(part, i) {
if (i % 2 === 0) {
frag.appendChild(document.createTextNode(part));
} else {
var span = document.createElement('span');
span.className = 'userscript-highlight';
span.textContent = part;
frag.appendChild(span);
}
});
node.parentNode.replaceChild(frag, node);
}
});
} else if (node.nodeType === 1 && node.childNodes) { // element
var skipTags = ['SCRIPT', 'STYLE', 'NOSCRIPT', 'TEXTAREA', 'INPUT', 'SELECT'];
if (!skipTags.includes(node.tagName)) {
Array.from(node.childNodes).forEach(highlight);
}
}
}
highlight(document.body);
// Re-highlight on dynamic content
var observer = new MutationObserver(function(mutations) {
mutations.forEach(function(m) {
m.addedNodes.forEach(function(node) {
if (node.nodeType === 1 || node.nodeType === 3) highlight(node);
});
});
});
observer.observe(document.body, { childList: true, subtree: true });
})();
}
} catch(__e) { console.warn('[Userscript:Highlight Search Terms]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

              Skip to content
              bug: output guardrail error message echoes the matched forbidden literal back to caller #153
              Closed
              #203
              Closed
              bug: output guardrail error message echoes the matched forbidden literal back to caller#153
              #203
              Labels
              bugSomething isn't workingpriority-normalvulnerability
              Description
              @moonming
              moonming
              opened on May 9, 2026
              Summary
              When an output guardrail with kind: "keyword" and hook_point: "output" blocks an upstream response containing a forbidden literal, the gateway's caller-visible error message includes the matched literal verbatim — defeating the purpose of an output guardrail (which exists precisely to keep forbidden content from reaching the caller).
              Repro
              E2E test attached: drafted as tests/e2e/src/cases/guardrail-output-e2e.test.ts (held back from #151 batch 2 PR pending this fix).
              Setup:
              • Mock upstream returns assistant message containing the literal "leakedsecret"
              • Output keyword guardrail configured with patterns: [{kind:"literal", value:"leakedsecret"}]
              • Caller sends an innocent prompt
              Observed:
              
```json
              
{
              
"error": {
              
"message": "content blocked by policy: output blocked by literal "leakedsecret"",
              
"type": "content_filter"
              
}
              
}
              
```
              The forbidden literal is right there in error.message. Anyone who can trigger the guardrail can extract the policy's blocklist by inspecting error responses.
              Expected:
              
```json
              
{
              
"error": {
              
"message": "response blocked by content policy",
              
"type": "content_filter"
              
}
              
}
              
```
              Or any redacted equivalent that does NOT include the matched pattern.
              Severity
              MEDIUM-HIGH for output guardrails specifically:
              • For input guardrails, leaking the matched pattern back is mostly cosmetic — the caller sent it, they already know.
              • For output guardrails, leaking the matched pattern is a real information leak — the whole point is to prevent the model's forbidden output from reaching the caller. Echoing it in the error envelope is a partial bypass.
              Proposed fix
              Strip / redact the matched value from the error rendered to clients. Internal logs may keep the matched pattern for operator debugging, but the wire-level error.message and any other caller-visible field must not carry it.
              Test attached
              The held-back test asserts:
              
```ts
              
const errorBlob = JSON.stringify(caught.error ?? {});
              
expect(errorBlob).not.toContain(FORBIDDEN_WORD);
              
```
              Will be added back to the e2e suite once this is fixed.
              Metadata
              Metadata
              Assignees
              No one assigned
                Labels
                bugSomething isn't workingpriority-normalvulnerability
                Type
                No type
                Projects
                No projects
                  Milestone
                  No milestone
                  Relationships
                  None yet
                  Development
                  No branches or pull requests
                  Issue actions
                  
, 'i');
if (__m === '*' || __re.test(location.href)) {
// Strip utm_, fbclid, gclid, etc. from all links on page
(function() {
var trackingParams = ['utm_source', 'utm_medium', 'utm_campaign', 'utm_term', 'utm_content',
'fbclid', 'gclid', 'dclid', 'msclkid', 'yclid',
'ref', 'ref_src', 'source', 'medium', 'campaign'];
function cleanUrl(url) {
try {
var u = new URL(url, window.location.origin);
var changed = false;
trackingParams.forEach(function(p) {
if (u.searchParams.has(p)) {
u.searchParams.delete(p);
changed = true;
}
});
return changed ? u.toString() : url;
} catch (e) {
return url;
}
}
function cleanLinks() {
document.querySelectorAll('a[href]').forEach(function(a) {
var clean = cleanUrl(a.href);
if (clean !== a.href) a.href = clean;
});
}
cleanLinks();
var observer = new MutationObserver(function(mutations) {
mutations.forEach(function(m) {
m.addedNodes.forEach(function(node) {
if (node.nodeType === 1) {
if (node.tagName === 'A') cleanLinks();
node.querySelectorAll('a[href]').forEach(function(a) {
var clean = cleanUrl(a.href);
if (clean !== a.href) a.href = clean;
});
}
});
});
});
observer.observe(document.body, { childList: true, subtree: true });
})();
}
} catch(__e) { console.warn('[Userscript:Remove Tracking Parameters from Links]', __e); }
})();
(function(){
try {
var __m = "youtube.com";
var __re = new RegExp('^' + "youtube\\.com" + '

                  Skip to content
                  bug: output guardrail error message echoes the matched forbidden literal back to caller #153
                  Closed
                  #203
                  Closed
                  bug: output guardrail error message echoes the matched forbidden literal back to caller#153
                  #203
                  Labels
                  bugSomething isn't workingpriority-normalvulnerability
                  Description
                  @moonming
                  moonming
                  opened on May 9, 2026
                  Summary
                  When an output guardrail with kind: "keyword" and hook_point: "output" blocks an upstream response containing a forbidden literal, the gateway's caller-visible error message includes the matched literal verbatim — defeating the purpose of an output guardrail (which exists precisely to keep forbidden content from reaching the caller).
                  Repro
                  E2E test attached: drafted as tests/e2e/src/cases/guardrail-output-e2e.test.ts (held back from #151 batch 2 PR pending this fix).
                  Setup:
                  • Mock upstream returns assistant message containing the literal "leakedsecret"
                  • Output keyword guardrail configured with patterns: [{kind:"literal", value:"leakedsecret"}]
                  • Caller sends an innocent prompt
                  Observed:
                  
```json
                  
{
                  
"error": {
                  
"message": "content blocked by policy: output blocked by literal "leakedsecret"",
                  
"type": "content_filter"
                  
}
                  
}
                  
```
                  The forbidden literal is right there in error.message. Anyone who can trigger the guardrail can extract the policy's blocklist by inspecting error responses.
                  Expected:
                  
```json
                  
{
                  
"error": {
                  
"message": "response blocked by content policy",
                  
"type": "content_filter"
                  
}
                  
}
                  
```
                  Or any redacted equivalent that does NOT include the matched pattern.
                  Severity
                  MEDIUM-HIGH for output guardrails specifically:
                  • For input guardrails, leaking the matched pattern back is mostly cosmetic — the caller sent it, they already know.
                  • For output guardrails, leaking the matched pattern is a real information leak — the whole point is to prevent the model's forbidden output from reaching the caller. Echoing it in the error envelope is a partial bypass.
                  Proposed fix
                  Strip / redact the matched value from the error rendered to clients. Internal logs may keep the matched pattern for operator debugging, but the wire-level error.message and any other caller-visible field must not carry it.
                  Test attached
                  The held-back test asserts:
                  
```ts
                  
const errorBlob = JSON.stringify(caught.error ?? {});
                  
expect(errorBlob).not.toContain(FORBIDDEN_WORD);
                  
```
                  Will be added back to the e2e suite once this is fixed.
                  Metadata
                  Metadata
                  Assignees
                  No one assigned
                    Labels
                    bugSomething isn't workingpriority-normalvulnerability
                    Type
                    No type
                    Projects
                    No projects
                      Milestone
                      No milestone
                      Relationships
                      None yet
                      Development
                      No branches or pull requests
                      Issue actions
                      
, 'i');
if (__m === '*' || __re.test(location.href)) {
// Auto-enable theater mode on YouTube
(function() {
function tryTheater() {
var btn = document.querySelector('button[aria-label="Theater mode"], ytd-player #player button[title="Theater mode"]');
if (btn && !btn.classList.contains('activated')) {
btn.click();
}
}
// Try immediately
tryTheater();
// Try after navigation (SPA)
var lastUrl = location.href;
setInterval(function() {
if (location.href !== lastUrl) {
lastUrl = location.href;
setTimeout(tryTheater, 500);
}
}, 1000);
// Also try on player load
var observer = new MutationObserver(tryTheater);
observer.observe(document.body, { childList: true, subtree: true });
})();
}
} catch(__e) { console.warn('[Userscript:YouTube Theater Mode Default]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

                      Skip to content
                      bug: output guardrail error message echoes the matched forbidden literal back to caller #153
                      Closed
                      #203
                      Closed
                      bug: output guardrail error message echoes the matched forbidden literal back to caller#153
                      #203
                      Labels
                      bugSomething isn't workingpriority-normalvulnerability
                      Description
                      @moonming
                      moonming
                      opened on May 9, 2026
                      Summary
                      When an output guardrail with kind: "keyword" and hook_point: "output" blocks an upstream response containing a forbidden literal, the gateway's caller-visible error message includes the matched literal verbatim — defeating the purpose of an output guardrail (which exists precisely to keep forbidden content from reaching the caller).
                      Repro
                      E2E test attached: drafted as tests/e2e/src/cases/guardrail-output-e2e.test.ts (held back from #151 batch 2 PR pending this fix).
                      Setup:
                      • Mock upstream returns assistant message containing the literal "leakedsecret"
                      • Output keyword guardrail configured with patterns: [{kind:"literal", value:"leakedsecret"}]
                      • Caller sends an innocent prompt
                      Observed:
                      
```json
                      
{
                      
"error": {
                      
"message": "content blocked by policy: output blocked by literal "leakedsecret"",
                      
"type": "content_filter"
                      
}
                      
}
                      
```
                      The forbidden literal is right there in error.message. Anyone who can trigger the guardrail can extract the policy's blocklist by inspecting error responses.
                      Expected:
                      
```json
                      
{
                      
"error": {
                      
"message": "response blocked by content policy",
                      
"type": "content_filter"
                      
}
                      
}
                      
```
                      Or any redacted equivalent that does NOT include the matched pattern.
                      Severity
                      MEDIUM-HIGH for output guardrails specifically:
                      • For input guardrails, leaking the matched pattern back is mostly cosmetic — the caller sent it, they already know.
                      • For output guardrails, leaking the matched pattern is a real information leak — the whole point is to prevent the model's forbidden output from reaching the caller. Echoing it in the error envelope is a partial bypass.
                      Proposed fix
                      Strip / redact the matched value from the error rendered to clients. Internal logs may keep the matched pattern for operator debugging, but the wire-level error.message and any other caller-visible field must not carry it.
                      Test attached
                      The held-back test asserts:
                      
```ts
                      
const errorBlob = JSON.stringify(caught.error ?? {});
                      
expect(errorBlob).not.toContain(FORBIDDEN_WORD);
                      
```
                      Will be added back to the e2e suite once this is fixed.
                      Metadata
                      Metadata
                      Assignees
                      No one assigned
                        Labels
                        bugSomething isn't workingpriority-normalvulnerability
                        Type
                        No type
                        Projects
                        No projects
                          Milestone
                          No milestone
                          Relationships
                          None yet
                          Development
                          No branches or pull requests
                          Issue actions
                          
, 'i');
if (__m === '*' || __re.test(location.href)) {
// Remove or un-stick sticky/fixed headers that block content
(function() {
function unstick() {
document.querySelectorAll('header, nav, [role="banner"], .header, .navbar, .sticky, .fixed-top, [style*="position: fixed"], [style*="position:sticky"]').forEach(function(el) {
if (el.style.position === 'fixed' || el.style.position === 'sticky' || getComputedStyle(el).position === 'fixed' || getComputedStyle(el).position === 'sticky') {
el.style.position = 'static';
el.style.top = 'auto';
el.style.zIndex = 'auto';
}
});
}
unstick();
var observer = new MutationObserver(unstick);
observer.observe(document.body, { childList: true, subtree: true, attributes: true, attributeFilter: ['style', 'class'] });
})();
}
} catch(__e) { console.warn('[Userscript:Kill Sticky Headers]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

                          Skip to content
                          bug: output guardrail error message echoes the matched forbidden literal back to caller #153
                          Closed
                          #203
                          Closed
                          bug: output guardrail error message echoes the matched forbidden literal back to caller#153
                          #203
                          Labels
                          bugSomething isn't workingpriority-normalvulnerability
                          Description
                          @moonming
                          moonming
                          opened on May 9, 2026
                          Summary
                          When an output guardrail with kind: "keyword" and hook_point: "output" blocks an upstream response containing a forbidden literal, the gateway's caller-visible error message includes the matched literal verbatim — defeating the purpose of an output guardrail (which exists precisely to keep forbidden content from reaching the caller).
                          Repro
                          E2E test attached: drafted as tests/e2e/src/cases/guardrail-output-e2e.test.ts (held back from #151 batch 2 PR pending this fix).
                          Setup:
                          • Mock upstream returns assistant message containing the literal "leakedsecret"
                          • Output keyword guardrail configured with patterns: [{kind:"literal", value:"leakedsecret"}]
                          • Caller sends an innocent prompt
                          Observed:
                          
```json
                          
{
                          
"error": {
                          
"message": "content blocked by policy: output blocked by literal "leakedsecret"",
                          
"type": "content_filter"
                          
}
                          
}
                          
```
                          The forbidden literal is right there in error.message. Anyone who can trigger the guardrail can extract the policy's blocklist by inspecting error responses.
                          Expected:
                          
```json
                          
{
                          
"error": {
                          
"message": "response blocked by content policy",
                          
"type": "content_filter"
                          
}
                          
}
                          
```
                          Or any redacted equivalent that does NOT include the matched pattern.
                          Severity
                          MEDIUM-HIGH for output guardrails specifically:
                          • For input guardrails, leaking the matched pattern back is mostly cosmetic — the caller sent it, they already know.
                          • For output guardrails, leaking the matched pattern is a real information leak — the whole point is to prevent the model's forbidden output from reaching the caller. Echoing it in the error envelope is a partial bypass.
                          Proposed fix
                          Strip / redact the matched value from the error rendered to clients. Internal logs may keep the matched pattern for operator debugging, but the wire-level error.message and any other caller-visible field must not carry it.
                          Test attached
                          The held-back test asserts:
                          
```ts
                          
const errorBlob = JSON.stringify(caught.error ?? {});
                          
expect(errorBlob).not.toContain(FORBIDDEN_WORD);
                          
```
                          Will be added back to the e2e suite once this is fixed.
                          Metadata
                          Metadata
                          Assignees
                          No one assigned
                            Labels
                            bugSomething isn't workingpriority-normalvulnerability
                            Type
                            No type
                            Projects
                            No projects
                              Milestone
                              No milestone
                              Relationships
                              None yet
                              Development
                              No branches or pull requests
                              Issue actions
                              
, 'i');
if (__m === '*' || __re.test(location.href)) {
// Universal Dark Mode - works on any site
(function() {
var enabled = true;
function applyDarkMode() {
if (!enabled) return;
// Create style element if it doesn't exist
var style = document.getElementById('universal-dark-mode-style');
if (!style) {
style = document.createElement('style');
style.id = 'universal-dark-mode-style';
document.head.appendChild(style);
}
// Dark mode CSS - inverts colors but preserves images/video
style.textContent = '
/* Invert everything except media */
html {
filter: invert(1) hue-rotate(180deg) !important;
background: #1a1a2e !important;
}
/* Restore images, videos, iframes, canvas */
img, video, iframe, canvas, svg, picture, [style*="background-image"] {
filter: invert(1) hue-rotate(180deg) !important;
}
/* Preserve specific elements that should not be inverted */
.no-dark-mode, .no-dark-mode *,
[data-theme="light"], [data-theme="light"],
.ace_editor, .ace_editor *,
.CodeMirror, .CodeMirror *,
.monaco-editor, .monaco-editor *,
.markdown-body pre, .markdown-body pre *,
.highlight, .highlight *,
pre code, pre code * {
filter: none !important;
}
/* Fix common UI elements */
.modal, .popup, .dropdown-menu, .tooltip, .popover {
filter: invert(1) hue-rotate(180deg) !important;
background: #2d2d44 !important;
border-color: #444 !important;
}
/* Scrollbars */
::-webkit-scrollbar { background: #1a1a2e !important; }
::-webkit-scrollbar-thumb { background: #444 !important; }
::-webkit-scrollbar-thumb:hover { background: #555 !important; }
/* Selection */
::selection { background: #4ecdc4 !important; color: #1a1a2e !important; }
::-moz-selection { background: #4ecdc4 !important; color: #1a1a2e !important; }
';
}
function removeDarkMode() {
var style = document.getElementById('universal-dark-mode-style');
if (style) style.remove();
}
// Toggle with Alt+Shift+D
document.addEventListener('keydown', function(e) {
if (e.altKey && e.shiftKey && e.key === 'D') {
e.preventDefault();
enabled = !enabled;
if (enabled) {
applyDarkMode();
console.log('[Universal Dark Mode] Enabled');
} else {
removeDarkMode();
console.log('[Universal Dark Mode] Disabled');
}
}
});
// Apply on load
applyDarkMode();
// Re-apply on dynamic content
var observer = new MutationObserver(function(mutations) {
if (enabled && !document.getElementById('universal-dark-mode-style')) {
applyDarkMode();
}
});
observer.observe(document.head, { childList: true });
console.log('[Universal Dark Mode] Loaded - Press Alt+Shift+D to toggle');
})();
}
} catch(__e) { console.warn('[Userscript:Universal Dark Mode]', __e); }
})();
})();

                              Skip to content
                              bug: output guardrail error message echoes the matched forbidden literal back to caller #153
                              Closed
                              #203
                              Closed
                              bug: output guardrail error message echoes the matched forbidden literal back to caller#153
                              #203
                              Labels
                              bugSomething isn't workingpriority-normalvulnerability
                              Description
                              @moonming
                              moonming
                              opened on May 9, 2026
                              Summary
                              When an output guardrail with kind: "keyword" and hook_point: "output" blocks an upstream response containing a forbidden literal, the gateway's caller-visible error message includes the matched literal verbatim — defeating the purpose of an output guardrail (which exists precisely to keep forbidden content from reaching the caller).
                              Repro
                              E2E test attached: drafted as tests/e2e/src/cases/guardrail-output-e2e.test.ts (held back from #151 batch 2 PR pending this fix).
                              Setup:
                              • Mock upstream returns assistant message containing the literal "leakedsecret"
                              • Output keyword guardrail configured with patterns: [{kind:"literal", value:"leakedsecret"}]
                              • Caller sends an innocent prompt
                              Observed:
                              
```json
                              
{
                              
"error": {
                              
"message": "content blocked by policy: output blocked by literal "leakedsecret"",
                              
"type": "content_filter"
                              
}
                              
}
                              
```
                              The forbidden literal is right there in error.message. Anyone who can trigger the guardrail can extract the policy's blocklist by inspecting error responses.
                              Expected:
                              
```json
                              
{
                              
"error": {
                              
"message": "response blocked by content policy",
                              
"type": "content_filter"
                              
}
                              
}
                              
```
                              Or any redacted equivalent that does NOT include the matched pattern.
                              Severity
                              MEDIUM-HIGH for output guardrails specifically:
                              • For input guardrails, leaking the matched pattern back is mostly cosmetic — the caller sent it, they already know.
                              • For output guardrails, leaking the matched pattern is a real information leak — the whole point is to prevent the model's forbidden output from reaching the caller. Echoing it in the error envelope is a partial bypass.
                              Proposed fix
                              Strip / redact the matched value from the error rendered to clients. Internal logs may keep the matched pattern for operator debugging, but the wire-level error.message and any other caller-visible field must not carry it.
                              Test attached
                              The held-back test asserts:
                              
```ts
                              
const errorBlob = JSON.stringify(caught.error ?? {});
                              
expect(errorBlob).not.toContain(FORBIDDEN_WORD);
                              
```
                              Will be added back to the e2e suite once this is fixed.
                              Metadata
                              Metadata
                              Assignees
                              No one assigned
                                Labels
                                bugSomething isn't workingpriority-normalvulnerability
                                Type
                                No type
                                Projects
                                No projects
                                  Milestone
                                  No milestone
                                  Relationships
                                  None yet
                                  Development
                                  No branches or pull requests
                                  Issue actions