GHSA-3wc5-fcw2-2329
MEDIUMKaTeX missing normalization of the protocol in URLs allows bypassing forbidden protocols
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.
Blast Radius
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Description
Impact
Code that uses KaTeX's trust option, specifically that provides a function to block-list certain URL protocols, can be fooled by URLs in malicious inputs that use uppercase characters in the protocol. In particular, this can allow for malicious input to generate javascript: links in the output, even if the trust function tries to forbid this protocol via trust: (context) => context.protocol !== 'javascript'.
Patches
Upgrade to KaTeX v0.16.10 to remove this vulnerability.
Workarounds
- Allow-list instead of block protocols in your
trustfunction. - Manually lowercase
context.protocolviacontext.protocol.toLowerCase()before attempting to check for certain protocols. - Avoid use of or turn off the
trustoption.
Details
KaTeX did not normalize the protocol entry of the context object provided to a user-specified trust-function, so it could be a mix of lowercase and/or uppercase letters.
It is generally better to allow-list by protocol, in which case this would normally not be an issue. But in some cases, you might want to block-list, and the KaTeX documentation even provides such an example:
Allow all commands but forbid specific protocol:
trust: (context) => context.protocol !== 'file'
Currently KaTeX internally sees file: and File: URLs as different protocols, so context.protocol can be file or File, so the above check does not suffice. A simple workaround would be:
trust: (context) => context.protocol.toLowerCase() !== 'file'
Most URL parsers normalize the scheme to lowercase. For example, RFC3986 says:
Although schemes are case-insensitive, the canonical form is lowercase and documents that specify schemes must do so with lowercase letters. An implementation should accept uppercase letters as equivalent to lowercase in scheme names (e.g., allow "HTTP" as well as "http") for the sake of robustness but should only produce lowercase scheme names for consistency.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | katex | ≥ 0.11.0&&< 0.16.10 | 0.16.10 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for katex. 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 katex to 0.16.10 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-3wc5-fcw2-2329 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-3wc5-fcw2-2329 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-3wc5-fcw2-2329. 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-3wc5-fcw2-2329 in your dependencies?
O3 detects GHSA-3wc5-fcw2-2329 across npm dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.