CVE-2026-55851Netty is a network application framework for development of protocol servers and clients.
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Netty is a network application framework for development of protocol servers and clients. In versions 4.2.0.Final up to (but not including) 4.2.16.Final, and 4.1.0.Final up to (but not including) 4.1.135, the `HAProxyMessageDecoder` in Netty's `codec-haproxy` module performs protocol version detection by reading the 13th byte as a signed Java `byte` and widening it to `int` without masking; a PROXY protocol v2 binary prefix followed by version byte `0xFF` sign-extends to `-1`, collides with the decoder's need-more-data sentinel, and causes `ByteToMessageDecoder` to accumulate inbound bytes in an unbounded `cumulation` buffer until direct memory is exhausted. This issue is fixed in versions 4.1.136.Final and 4.2.16.Final.
- CVSS
- 7.5 HIGH (v3.1, NVD)CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- Weakness (CWE)
- CWE-400
- Known exploited
- Not in CISA's KEV catalog
- EPSS (exploitation in the next 30 days)
- Not loaded for this CVE
- Assigned by
- Not given
- NVD analysis
- Analyzed
- Record last updated
- Jul 30, 2026
- First seen by InfoSec Signals
- Oct 9, 2026
Affected products
netty netty netty:netty | from 4.1.0 before 4.1.136; from 4.2.0 before 4.2.16 | NVD |
References
- https://github.com/netty/netty/commit/5b68c61f37aa4a3045cba624cbea239655c9003bpatch
- https://github.com/netty/netty/commit/bb2ff68a1fb71cb4b0eb9a9e17b66c52aff680c6patch
- https://github.com/netty/netty/releases/tag/netty-4.1.136.Finalrelease-notes
- https://github.com/netty/netty/releases/tag/netty-4.2.16.Finalrelease-notes
- https://github.com/netty/netty/security/advisories/GHSA-q6cq-mhr2-jmr5vendor-advisory
The CVE record on cve.org NVD's entry
The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.