Vulnerability in Io.netty Netty-Codec-Http

CVE-2026-42584

Netty is an asynchronous, event-driven network application framework. Prior to 4.2.13.Final and 4.1.133.Final, HttpClientCodec pairs each inbound response with an outbound request by queue.poll() once per response, including for 1xx. If the client pipelines GET then HEAD and the server sends 103, then 200 with GET body, then 200 for HEAD, the queue pairs HEAD with the first 200. The HEAD rule then skips reading that message’s body, so the GET entity bytes stay on the stream and the following 200 is parsed from the wrong offset. 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 7.3 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L.

EPSS exploit prediction

EPSS: 0.007 (51.9th percentile), scored .

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 52nd percentile — 51.9% 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-2026-42584: held from 0.008 to 0.007.

EPSS over last 30 days · oldest: 0.008 · newest: 0.007 · change: -0.001

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-2026-42584?
CVE-2026-42584 is a high-severity vulnerability in Io.netty Netty-Codec-Http, classified under Inconsistent Interpretation of HTTP Requests (HTTP Request/Response Smuggling). CVSS score: 7.3/10. Published 2026-05-13.
How severe is CVE-2026-42584?
High severity. CVSS v3 base score is 7.3 out of 10.