Integer overflow in Io.netty Netty-Codec-Http

CVE-2026-42580

Netty is an asynchronous, event-driven network application framework. Prior to 4.2.13.Final and 4.1.133.Final, Netty's chunk size parser silently overflows int, enabling request smuggling attacks. This vulnerability is fixed in 4.2.13.Final and 4.1.133.Final.

Vulnerability class: Integer Overflow

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:N/I:L/A:L.

EPSS exploit prediction

EPSS: 0.004 (27.5th percentile), scored .

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 28th percentile — 27.5% 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-2026-42580: held from 0.004 to 0.004.

EPSS over last 30 days · oldest: 0.004 · newest: 0.004 · 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-2026-42580?
CVE-2026-42580 is a medium-severity vulnerability in Io.netty Netty-Codec-Http, classified under Integer Overflow or Wraparound. CVSS score: 6.5/10. Published 2026-05-13.
How severe is CVE-2026-42580?
Medium severity. CVSS v3 base score is 6.5 out of 10.