GHSA-55xv-f85c-248q
LOWRegular Expression Denial of Service (ReDoS) in jsx-slack
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
jsx-slackReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects npm packages — download data is not available via public APIs for these ecosystems.
Description
jsx-slack v4.5.1 and earlier versions are vulnerable to a regular expression denial-of-service (ReDoS) attack.
Impact
If attacker can put a lot of JSX elements into <blockquote> tag, an internal regular expression for escaping characters may consume an excessive amount of computing resources.
/** @jsxImportSource jsx-slack */
import { Section } from 'jsx-slack'
console.log(
<Section>
<blockquote>
{[...Array(40)].map((_, i) => (
<p>{i + 1}</p>
))}
</blockquote>
</Section>
)
Patches
See also: https://github.com/yhatt/jsx-slack/security/advisories/GHSA-hp68-xhvj-x6j6
jsx-slack v4.5.2 has updated regular expressions to prevent catastrophic backtracking.
jsx-slack v4.5.1 also had patched a workaround. It has no problems to contents with ASCII characters, but still vulnerable to contents with multibyte characters. (https://github.com/yhatt/jsx-slack/commit/36e4a10405e4c7745333e245fcc5029c02c7065d)
References
- https://nvd.nist.gov/vuln/detail/CVE-2021-43838
- https://github.com/yhatt/jsx-slack/commit/36e4a10405e4c7745333e245fcc5029c02c7065d
Credits
Thanks to @hieki for finding out this vulnerability.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | jsx-slack | all versions | 4.5.1 |
Research use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for jsx-slack. 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 jsx-slack to 4.5.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-55xv-f85c-248q 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-55xv-f85c-248q 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-55xv-f85c-248q. 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-55xv-f85c-248q in your dependencies?
O3 detects GHSA-55xv-f85c-248q across npm dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.