GHSA-4cwx-7wf7-3272 is a high-severity (CVSS 7.4) Information Exposure vulnerability in undici. A fix is available for undici — see the affected versions and patch details below.
undici vulnerable to cross-user information disclosure and parse-time crash via degenerate private cache directives
Exploitation Status
No confirmed exploitation observed yet
- A successful exploit gives an attacker total control of the affected component, not partial access.
- 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-4cwx-7wf7-3272.
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-4cwx-7wf7-3272 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 374,847 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
Summary
Two issues in undici's cache interceptor, both fixed by the same patch on lib/util/cache.js:
- Shared-cache disclosure: Responses with malformed qualified
Cache-Control: privatedirectives such asprivate=""orprivate=","can be incorrectly stored in the default shared cache, then served to a later caller with the same cache key. - Parse-time crash: Mixed unqualified-and-qualified
privatedirectives in the same header (such aspublic, max-age=60, private, private="hdr") cause an uncaughtTypeErrorin the cache-control parser, terminating the request.
Impact
Shared-cache disclosure
Applications using interceptors.cache() in shared mode may cache a user-specific response and serve it to a later caller with the same cache key. This can disclose private response bodies and headers, including Set-Cookie.
Required conditions:
- the cache interceptor is enabled in shared mode, including the default configuration;
- an upstream returns a malformed directive such as
Cache-Control: public, max-age=300, private=""; - another request later matches the same cache key, without a separating
Varyheader.
Parse-time crash
Applications using interceptors.cache() against an upstream that returns a Cache-Control header combining unqualified private with qualified private="..." see an uncaught TypeError: output.private.concat is not a function during response handling. The request rejects; depending on the consumer's error handling, the process may exit.
Details
private="" is parsed as { private: [''] }. The shared-cache guard only rejects private === true, so the response can be stored. When served from cache, the previous user's body and headers may be returned to a different user.
For the crash variant, an unqualified private directive sets output.private = true, then a subsequent qualified private="hdr" directive attempts output.private.concat(['hdr']), which throws because boolean has no concat method.
The patch routes the qualified-directive path through a shared helper that normalizes empty-after-trim arrays to true and preserves existing true values, closing both vectors.
Patches
Upgrade to undici 7.29.0 or 8.9.0. Both releases fix the qualified private directive handling that caused the shared-cache storage and the parser crash.
Workarounds
Until patched, avoid shared interceptors.cache() for user-specific responses, use type: 'private', or disable caching for affected origins.
Credit
Disclosure variant reported by @h0rk1p via HackerOne report #3817497.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | undici | ≥ 7.0.0&&< 7.29.0 | 7.29.0npm install undici@7.29.0 |
| 📦npm | undici | ≥ 8.0.0&&< 8.9.0 | 8.9.0npm install undici@8.9.0 |
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 7.29.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-4cwx-7wf7-3272 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-4cwx-7wf7-3272 can be triaged on real exposure rather than presence alone.
Tailored to GHSA-4cwx-7wf7-3272. 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 Hardened Images | nodejs26-main-26.5.1-1.5.hum1 | RHSA-2026:48273 |
| Red Hat Hardened Images | nodejs24-main-24.18.1-0.1.hum1 | RHSA-2026:48537 |
Frequently Asked Questions
Is GHSA-4cwx-7wf7-3272 in your dependencies?
O3 Security finds GHSA-4cwx-7wf7-3272 across npm dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.