Vulnerability in Netty
CVE-2026-59903
Netty is an asynchronous, event-driven network application framework. Prior to 4.1.137.Final and 4.2.17.Final, io.netty.handler.codec.http.cors.CorsHandler setVaryHeader replaces application Vary headers such as Authorization or Cookie with Origin, allowing a caching proxy or CDN to reuse authenticated responses across users and disclose sensitive information. This issue is fixed in versions 4.1.137.Final and 4.2.17.Final.
Published · last modified .
CVSS v3 metric
CVSS v3 base score 6.5 (Medium). Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:L/A:N.
EPSS exploit prediction
EPSS: 0.002 (14.3th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 14th percentile — 14.3% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.002 · newest: 0.002 · change: +0.000
Affected products
- Netty — versions < 4.1.137.Final, >= 4.2.0.Final, < 4.2.17.Final
Weakness classification (CWE)
Public proof-of-concept exploits
References
- github.com/netty/netty/pull/17213 (Patch, Issue Tracking)
- github.com/netty/netty/pull/17217 (Patch, Issue Tracking)
- github.com/netty/netty/releases/tag/netty-4.1.137.Final (Release Notes)
- github.com/netty/netty/releases/tag/netty-4.2.17.Final (Release Notes)
- github.com/netty/netty/security/advisories/GHSA-8c42-7qj2-3j46 (Vendor Advisory)
Frequently asked questions
- What is CVE-2026-59903?
- CVE-2026-59903 is a medium-severity vulnerability in Netty, classified under Use of Cache Containing Sensitive Information. CVSS score: 6.5/10. Published 2026-08-17.
- How severe is CVE-2026-59903?
- Medium severity. CVSS v3 base score is 6.5 out of 10.
- Is CVE-2026-59903 known to be exploited?
- 1 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.