GHSA-r6ch-mqf9-qc9w is a high-severity (CVSS 7.5) Improper Input Validation vulnerability in undici. A fix is available for undici — see the affected versions and patch details below.
Regular Expression Denial of Service in Headers
Exploitation Status
No confirmed exploitation observed yet
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
- 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-r6ch-mqf9-qc9w.
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-r6ch-mqf9-qc9w 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 377,333 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.
undicinpmDescription
Impact
The Headers.set() and Headers.append() methods are vulnerable to Regular Expression Denial of Service (ReDoS) attacks when untrusted values are passed into the functions. This is due to the inefficient regular expression used to normalize the values in the headerValueNormalize() utility function.
Patches
This vulnerability was patched in v5.19.1.
Workarounds
There is no workaround. Please update to an unaffected version.
References
Credits
Carter Snook reported this vulnerability.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | undici | all versions | 5.19.1npm install undici@5.19.1 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for undici, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update undici to 5.19.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-r6ch-mqf9-qc9w 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 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like GHSA-r6ch-mqf9-qc9w can be triaged on real exposure rather than presence alone.
Tailored to GHSA-r6ch-mqf9-qc9w. 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.
| Product | Fixed in | Advisory |
|---|---|---|
| Red Hat Enterprise Linux 8 | nodejs:16-8070020230314140722.bd1311ed | RHSA-2023:1582 |
| Red Hat Enterprise Linux 8 | nodejs:18-8070020230322080930.bd1311ed | RHSA-2023:1583 |
| Red Hat Enterprise Linux 9 | nodejs:18-9020020230327152102.rhel9 | RHSA-2023:2654 |
| Red Hat Enterprise Linux 9 | nodejs-1:16.19.1-1.el9_2 | RHSA-2023:2655 |
| Red Hat Enterprise Linux 9.0 Extended Update Support | nodejs-1:16.20.2-1.el9_0 | RHSA-2023:5533 |
Frequently Asked Questions
Is GHSA-r6ch-mqf9-qc9w in your dependencies?
O3 Security finds GHSA-r6ch-mqf9-qc9w across npm dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.