What is CVE-2026-89044?

CVE-2026-89044 is a medium-severity vulnerability in Netty, classified under Inconsistent Interpretation of HTTP Requests (HTTP Request/Response Smuggling). CVSS score: 6.5/10. Published 2026-09-10.

How severe is CVE-2026-89044?

Medium severity. CVSS v3 base score is 6.5 out of 10.

Vulnerability in Netty

CVE-2026-89044

Netty versions 4.1.133.Final through 4.1.137.Final and 4.2.13.Final through 4.2.17.Final fail to properly validate the final transfer coding in the Transfer-Encoding header, allowing attackers to smuggle requests by using malformed encoding declarations. Attackers can split Transfer-Encoding headers across multiple lines or use values like 'chunked, xchunked' to bypass validation and decode messages as chunked when the final coding is not chunked, enabling request smuggling attacks.

Vulnerability class: HTTP Request Smuggling

Published 2026-09-10 · last modified 2026-09-18.

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 (20.7th percentile), scored 2026-10-26.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 21st percentile — 20.7% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.004 · newest: 0.003 · change: -0.001

Affected products

Netty

Weakness classification (CWE)

CWE-444 — Inconsistent Interpretation of HTTP Requests (HTTP Request/Response Smuggling)

References

github.com/netty/netty/security/advisories/GHSA-hcvj-94mj-jp5c (Exploit, vendor-advisory, Vendor Advisory)
github.com/netty/netty/commit/ca87393b0e9e13c493d213a268e727a6d44e1585 (Patch, patch)
github.com/netty/netty/commit/640d4d3324f7b811a4903d0730c8ccb35500500c (Patch, patch)
github.com/netty/netty/blob/netty-4.1.137.Final/codec-http/src/main/java/io/net… (Product, technical-description)
github.com/netty/netty/releases/tag/netty-4.1.138.Final (release-notes, Release Notes)
github.com/netty/netty/releases/tag/netty-4.2.18.Final (release-notes, Release Notes)
github.com/netty/netty (Product, product)
www.vulncheck.com/advisories/netty-4.1.133-final-through-4.1.137-final-and-4.2… (Patch, Third Party Advisory, third-party-advisory)

Frequently asked questions

What is CVE-2026-89044?: CVE-2026-89044 is a medium-severity vulnerability in Netty, classified under Inconsistent Interpretation of HTTP Requests (HTTP Request/Response Smuggling). CVSS score: 6.5/10. Published 2026-09-10.
How severe is CVE-2026-89044?: Medium severity. CVSS v3 base score is 6.5 out of 10.