{"id":"CVE-2026-55851","aliases":["GHSA-q6cq-mhr2-jmr5"],"url":"https://o3.security/vulnerability/CVE-2026-55851","summary":"Netty codec-haproxy: Signed-Byte Sentinel Collision in HAProxyMessageDecoder Leads to Unbounded Memory Exhaustion","details":"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.","published":"2026-07-21T21:22:34.879Z","modified":"2026-08-12T16:41:23.898939Z","cvss":null,"epss":{"score":0.00612,"percentile":0.4701,"asOf":"2026-09-04"},"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"Maven","name":"io.netty:netty-codec-haproxy","fixedVersion":"4.2.16.Final"},{"ecosystem":"Maven","name":"io.netty:netty-codec-haproxy","fixedVersion":"4.1.136.Final"}],"fix":{"url":"https://github.com/netty/netty/commit/5b68c61f37aa4a3045cba624cbea239655c9003b","label":"netty/netty@5b68c61"},"references":[{"type":"WEB","url":"https://github.com/netty/netty/releases/tag/netty-4.1.136.Final"},{"type":"WEB","url":"https://github.com/netty/netty/releases/tag/netty-4.2.16.Final"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/55xxx/CVE-2026-55851.json"},{"type":"ADVISORY","url":"https://github.com/netty/netty/security/advisories/GHSA-q6cq-mhr2-jmr5"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-55851"},{"type":"FIX","url":"https://github.com/netty/netty/commit/5b68c61f37aa4a3045cba624cbea239655c9003b"},{"type":"FIX","url":"https://github.com/netty/netty/commit/bb2ff68a1fb71cb4b0eb9a9e17b66c52aff680c6"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-08-12T16:41:23.898939Z"}}