GHSA-xcj9-5m2h-648r
Fix: mermaid-js/mermaid@8fead23GHSA-xcj9-5m2h-648r is a Code Injection vulnerability in mermaid. O3 Security confirms whether GHSA-xcj9-5m2h-648r is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
Mermaid: Improper sanitization of `classDefs` in diagrams leads to CSS injection
Exploitation Status
No confirmed exploitation observed yet
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for GHSA-xcj9-5m2h-648r.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
Real-World Exposure
How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.
mermaidnpmDescription
Details
The state diagram and any other diagram type that routes user-controlled style strings through createCssStyles parser for Mermaid v11.14.0 and earlier captures classDef values with an unrestricted regex:
// packages/mermaid/src/diagrams/state/parser/stateDiagram.jison:83
<CLASSDEFID>[^\n]* { this.popState(); return 'CLASSDEF_STYLEOPTS' }
The value passes unsanitized through addStyleClass() -> createCssStyles() -> style.innerHTML (mermaidAPI.ts:418). A } in the value closes the generated CSS selector, and everything after becomes a new CSS rule on the page.
PoC
stateDiagram-v2
classDef x }*{ background-image: url("http://media.giphy.com/media/SggILpMXO7Xt6/giphy.gif")}
Patches
This has been patched in:
- v11.15.0 (see e9b0f34d8d82a6260077764ee45e1d7d90957a0f)
- v10.9.6 (see 8fead23c59166b7bab6a39eac81acebee2859102)
Workarounds
Setting "securityLevel": "sandbox" will prevent this, by rendering the mermaid diagram in a sandboxed <iframe>.
Impact
Enables page defacement, user tracking via url() callbacks, and DOM attribute exfiltration via CSS :has() selectors.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | mermaid | ≥ 11.0.0-alpha.1&&< 11.15.0 | 11.15.0 |
| 📦npm | mermaid | all versions | 10.9.6 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for mermaid. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update mermaid to 11.15.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-xcj9-5m2h-648r is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether GHSA-xcj9-5m2h-648r is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to GHSA-xcj9-5m2h-648r. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is GHSA-xcj9-5m2h-648r in your dependencies?
O3 detects GHSA-xcj9-5m2h-648r across npm dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.