What’s Vulnerable › Vulnerabilities

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

• Severity: high (CVSS 7.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.5% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-06-18 · updated 2026-10-26
• Weakness: CWE-476

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.

Affected products

• HAProxy: before 2.4.36; from 2.5 before 2.6.30; from 2.7 before 2.8.25; from 2.9 before 3.0.24; from 3.1 before 3.2.20; from 3.3 before 3.4.1 — fixed in 2.4.36, 2.6.30, 2.8.25, 3.0.24, 3.2.20, 3.4.1

How to fix

Upgrade to a fixed version: HAProxy 2.4.36, 2.6.30, 2.8.25, 3.0.24. Check the vendor advisory for mitigations.

References

• https://github.com/haproxy/haproxy/commit/9a6d1fe3f00d86ab4ea6ea6ea0a5d48fc058a513
• https://www.vulncheck.com/advisories/haproxy-null-pointer-dereference-in-hpack-dht-insert-function

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