Vulnerability in Io.netty Netty-Codec-Http

CVE-2026-42585

Netty is an asynchronous, event-driven network application framework. Prior to 4.2.13.Final and 4.1.133.Final, Netty incorrectly parses malformed Transfer-Encoding, enabling request smuggling attacks. This vulnerability is fixed in 4.2.13.Final and 4.1.133.Final.

Vulnerability class: HTTP Request Smuggling

Published · last modified .

CVSS v3 metric

CVSS v3 base score 6.5 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N.

EPSS exploit prediction

EPSS: 0.003 (19.6th percentile), scored .

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 20th percentile — 19.6% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS trend (30 days)EPSS over the last 30 days for CVE-2026-42585: held from 0.002 to 0.003.

EPSS over last 30 days · oldest: 0.002 · newest: 0.003 · change: +0.000

Affected products

  • Io.netty Netty-Codec-Http — versions >= 4.2.0.Alpha1, < 4.2.13.Final, < 4.1.133.Final
  • Netty — versions >= 4.2.0.Alpha1, < 4.2.13.Final, < 4.1.133.Final

Weakness classification (CWE)

References

Frequently asked questions

What is CVE-2026-42585?
CVE-2026-42585 is a medium-severity vulnerability in Io.netty Netty-Codec-Http, classified under Inconsistent Interpretation of HTTP Requests (HTTP Request/Response Smuggling). CVSS score: 6.5/10. Published 2026-05-13.
How severe is CVE-2026-42585?
Medium severity. CVSS v3 base score is 6.5 out of 10.