CVE-2026-55204 HAProxy - NULL Pointer Dereference in hpack_dht_insert Function

High 8.7 Published 18 Jun 2026 Updated 14 Jul 2026

An attacker can crash HAProxy worker processes by triggering a null pointer dereference during HPACK table insertions under memory pressure.

Exploited in the wild: Not known
Login needed: Not needed
Attackable: Over the internet
Victim action needed: Not needed
Fix: Available

What is CVE-2026-55204?

CVE-2026-55204 is a high-severity vulnerability in haproxy, published on 18 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

Official description

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.

Weakness: CWE-476

Which versions are affected by CVE-2026-55204?

1 open source package ship an affected version, including haproxy. It affects 1 product.

Package	Affected	Fixed in
`haproxy` Bitnami	All versions	`2.4.36, 2.6.30, 2.8.25, 3.0.24, 3.2.20, 3.4.1`

Linux distribution packages (23)

`haproxy` AlmaLinux:8	All versions	`1.8.27-5.el8_10.2`
`haproxy` Red Hat:enterprise_linux:8::appstream	All versions	`0:1.8.27-5.el8_10.2`
`haproxy-debuginfo` Red Hat:enterprise_linux:8::appstream	All versions	`0:1.8.27-5.el8_10.2`
`haproxy-debugsource` Red Hat:enterprise_linux:8::appstream	All versions	`0:1.8.27-5.el8_10.2`
`haproxy` Red Hat:rhel_aus:8.4::appstream	All versions	`0:1.8.27-2.el8_4.2`
`haproxy-debuginfo` Red Hat:rhel_aus:8.4::appstream	All versions	`0:1.8.27-2.el8_4.2`
`haproxy-debugsource` Red Hat:rhel_aus:8.4::appstream	All versions	`0:1.8.27-2.el8_4.2`
`haproxy` Red Hat:rhel_aus:8.6::appstream	All versions	`0:1.8.27-4.el8_6.2`
`haproxy-debuginfo` Red Hat:rhel_aus:8.6::appstream	All versions	`0:1.8.27-4.el8_6.2`
`haproxy-debugsource` Red Hat:rhel_aus:8.6::appstream	All versions	`0:1.8.27-4.el8_6.2`
`haproxy` Red Hat:rhel_e4s:8.8::appstream	All versions	`0:1.8.27-5.el8_8.2`
`haproxy-debuginfo` Red Hat:rhel_e4s:8.8::appstream	All versions	`0:1.8.27-5.el8_8.2`
`haproxy-debugsource` Red Hat:rhel_e4s:8.8::appstream	All versions	`0:1.8.27-5.el8_8.2`
`haproxy` Red Hat:rhel_eus_long_life:8.4::appstream	All versions	`0:1.8.27-2.el8_4.2`
`haproxy-debuginfo` Red Hat:rhel_eus_long_life:8.4::appstream	All versions	`0:1.8.27-2.el8_4.2`
`haproxy-debugsource` Red Hat:rhel_eus_long_life:8.4::appstream	All versions	`0:1.8.27-2.el8_4.2`
`haproxy` Red Hat:rhel_eus_long_life:8.6::appstream	All versions	`0:1.8.27-4.el8_6.2`
`haproxy-debuginfo` Red Hat:rhel_eus_long_life:8.6::appstream	All versions	`0:1.8.27-4.el8_6.2`
`haproxy-debugsource` Red Hat:rhel_eus_long_life:8.6::appstream	All versions	`0:1.8.27-4.el8_6.2`
`haproxy` Red Hat:rhel_tus:8.8::appstream	All versions	`0:1.8.27-5.el8_8.2`
`haproxy-debuginfo` Red Hat:rhel_tus:8.8::appstream	All versions	`0:1.8.27-5.el8_8.2`
`haproxy-debugsource` Red Hat:rhel_tus:8.8::appstream	All versions	`0:1.8.27-5.el8_8.2`
`haproxy` Rocky Linux:8	All versions	`0:1.8.27-5.el8_10.2`

Products include Haproxy Haproxy.

How do I fix CVE-2026-55204?

Upgrade haproxy to a fixed version for your release line: 2.4.36, 2.6.30, 2.8.25 or 3.0.24.

Is CVE-2026-55204 being exploited?

There is no known exploitation of CVE-2026-55204 in the wild and no public exploit code.

Sources

Also known as ALSA-2026:55859, AZL-90261, BIT-haproxy-2026-55204, CLSA-2026-1782820521, CLSA-2026-1782825341, CLSA-2026-1782825734 and 20 more.