GHSA-8c42-7qj2-3j46 is a medium-severity (CVSS 6.5) CWE-524 vulnerability in io.netty:netty-codec-http. O3 Security confirms whether GHSA-8c42-7qj2-3j46 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
Netty Vulnerable to Cache Poisoning and Information Disclosure via CORS Vary Header Overwrite
Exploitation Status
No confirmed exploitation observed yet
- 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-8c42-7qj2-3j46.
Real-World Exposure
io.netty:netty-codec-http☕io.netty:netty-codec-httpReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Maven packages — download data is not available via public APIs for these ecosystems.
Description
Summary
Netty's CorsHandler silently overwrites existing Vary headers, enabling cache poisoning and sensitive information disclosure.
Details
io.netty.handler.codec.http.cors.CorsHandler#setVaryHeader overwrites any existing Vary headers set by backend applications.
private static void setVaryHeader(final HttpResponse response) {
response.headers().set(HttpHeaderNames.VARY, HttpHeaderNames.ORIGIN);
}
Because set() replaces all existing values for the header, if a backend application sets a Vary header (such as Vary: Authorization or Vary: Cookie) to ensure that intermediate caches (like CDNs) cache responses separately per user, the CorsHandler will overwrite it with Vary: origin. This causes the caching proxy to ignore the authorization context and cache the response based solely on the URL and Origin, allowing an attacker to retrieve another user's cached sensitive data.
Impact
This is a Cache Poisoning vulnerability that leads to Information Disclosure. It impacts any Netty-based web application that uses the CorsHandler, sets its own Vary headers to manage caching of authenticated or user-specific responses (e.g., Vary: Authorization), and is deployed behind a caching proxy or CDN. The end-users of these applications are impacted, as their sensitive data may be leaked to unauthorized actors.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| ☕Maven | io.netty:netty-codec-http | ≥ 4.2.0.Final&&< 4.2.17.Final | 4.2.17.Final |
| ☕Maven | io.netty:netty-codec-http | all versions | 4.1.137.Final |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for io.netty:netty-codec-http. 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 io.netty:netty-codec-http to 4.2.17.Final or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-8c42-7qj2-3j46 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-8c42-7qj2-3j46 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-8c42-7qj2-3j46. 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-8c42-7qj2-3j46 in your dependencies?
O3 detects GHSA-8c42-7qj2-3j46 across Maven dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.