GHSA-w9m9-85wc-3x92 is a medium-severity (CVSS 4.3) vulnerability in postcss-selector-parser. O3 Security confirms whether GHSA-w9m9-85wc-3x92 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
postcss-selector-parser allows denial of service through uncontrolled AST recursion
Exploitation Status
Proof-of-concept exploit code exists
- CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.
Exploitation and automatability from CISA’s SSVC triage for GHSA-w9m9-85wc-3x92.
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.
How urgent is this, really
GHSA-w9m9-85wc-3x92 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 371,256 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
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.
postcss-selector-parsernpmDescription
A vulnerability was determined in postcss-selector-parser before 6.1.3 and 7.1.1. Affected is the function toString of the file src/selectors/container.js of the component AST Serialization. Executing a manipulation can lead to uncontrolled recursion. It is possible to launch the attack remotely. The exploit has been publicly disclosed and may be utilized. The vendor explains, that according to his definition "DoS on server-side on user-generated CSS is low risk for us (since most users compile own CSS with PostCSS)."
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | postcss-selector-parser | ≥ 6.1.0&&< 6.1.3 | 6.1.3 |
| 📦npm | postcss-selector-parser | ≥ 7.1.0&&< 7.1.3 | 7.1.3 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for postcss-selector-parser. 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 postcss-selector-parser to 6.1.3 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-w9m9-85wc-3x92 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-w9m9-85wc-3x92 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-w9m9-85wc-3x92. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Fixing This On Your OS
If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.
Moderate: This flaw in Postcss can lead to a denial of service (DoS) in applications that process untrusted CSS. The vulnerability arises from uncontrolled recursion in the AST Serialization component when handling specially crafted CSS. Exploitation requires user interaction, such as submitting attacker-controlled…
Frequently Asked Questions
Is GHSA-w9m9-85wc-3x92 in your dependencies?
O3 detects GHSA-w9m9-85wc-3x92 across npm dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.