GHSA-66ww-999q-mffq — post-loader
CRITICALGHSA-66ww-999q-mffq is a critical-severity (CVSS 9.8) Cross-site Scripting (XSS) vulnerability in post-loader. 1 public exploit reference exists, so weaponization risk is real. No vendor fix is recorded yet; mitigation options are listed below.
Arbitrary code execution in post-loader
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-66ww-999q-mffq 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 378,567 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.
post-loadernpmDescription
post-loader is webpack loader for blog posts written in Markdown. The package post-loader from 0.0.0 is vulnerable to Arbitrary Code Execution which uses a markdown parser in an unsafe way so that any javascript code inside the markdown input files gets evaluated and executed. At this time, there is no known workaround or patch available.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | post-loader | ≥ 0.0.0 | No fix |
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 post-loader, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Remediation status
No patched version of post-loader has shipped for GHSA-66ww-999q-mffq yet. Where your build allows, override or pin the dependency away from the vulnerable range, and apply any maintainer-recommended mitigation.
Mitigate without a patch
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 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like GHSA-66ww-999q-mffq can be triaged on real exposure rather than presence alone.
Tailored to GHSA-66ww-999q-mffq. 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-66ww-999q-mffq in your dependencies?
O3 Security finds GHSA-66ww-999q-mffq across npm dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.