CVE-2026-55204: Haproxy

High severity, CVSS 7.5. EPSS: 0.5% chance of exploitation in the next 30 days.

HAProxy through 3.4.0, fixed in commit 9a6d1fe, contains a null pointer dereference vulnerability in hpack_dht_insert() within src/hpack-tbl.c that fails to validate the return value of hpack_dht_defrag() when the memory pool is exhausted. An attacker can trigger HPACK dynamic table insertions under memory pressure to dereference a NULL pointer and crash HAProxy worker processes, causing denial of service.

Affected products

• Haproxy Haproxy: before 2.4.36 (fixed in 2.4.36); from 2.5, before 2.6.30 (fixed in 2.6.30); from 2.7, before 2.8.25 (fixed in 2.8.25); from 2.9, before 3.0.24 (fixed in 3.0.24); from 3.1, before 3.2.20 (fixed in 3.2.20); from 3.3, before 3.4.1 (fixed in 3.4.1)

Published 2026-06-18. Last modified 2026-10-08.