CVE-2026-55204
HighCVSS 7.5Exploitation Probability (EPSS)
Low risk35th percentile - higher than 35% of all known CVEs
Summary
HAProxy up to version 3.4.0 contains a null pointer dereference vulnerability in the hpack_dht_insert() function in src/hpack-tbl.c. The flaw occurs when hpack_dht_defrag() returns null due to memory pool exhaustion and its return value is not validated. An attacker can exploit this by triggering HPACK dynamic table insertions under memory pressure, causing HAProxy worker processes to crash and resulting in denial of service.
Risk Assessment
The risk is that an unauthenticated attacker can remotely crash HAProxy, leading to service disruption and potential application unavailability.
Recommendation
It is recommended to immediately upgrade HAProxy to a version containing commit 9a6d1fe or later, which fixes the vulnerability. If an upgrade is not possible, restrict access to the service and monitor memory usage.
Original NVD description (English source)
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.