CVE-2026-55204: haproxy before 2.4.36 (exclusive), from 2.5 (inclusive), before 2.6.30 (exclusive), from 2.7 (inclusive), before…

Affected technology

haproxy · before 2.4.36 (exclusive)
haproxy

haproxy · from 2.5 (inclusive), before 2.6.30 (exclusive)
haproxy

haproxy · from 2.7 (inclusive), before 2.8.25 (exclusive)
haproxy

haproxy · from 2.9 (inclusive), before 3.0.24 (exclusive)
haproxy

haproxy · from 3.1 (inclusive), before 3.2.20 (exclusive)
haproxy

haproxy · from 3.3 (inclusive), before 3.4.1 (exclusive)
haproxy

haproxy · 0 through 3.4.0
haproxy

Description’s affected range: through 3.4.0, fixed in commit 9a6d1fe,

Component: Not specified by the source

Attack conditions (Vendor/CNA, CVSS 4.0): Network (remote) · No privileges required · No user interaction required

What an attacker can do

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. Vendor/CNA’s CVSS 4.0 assessment (base score 8.7/10) rates confidentiality and integrity impact as none; availability impact as high.