NULL pointer dereference in Haproxy
CVE-2026-55204
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.
Published · last modified .
CVSS v3 metric
CVSS v3 base score 7.5 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.
EPSS exploit prediction
EPSS: 0.005 (39.2th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 39th percentile — 39.2% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.005 · newest: 0.005 · change: 0.000
Affected products
- Haproxy — versions 0, 9a6d1fe3f00d86ab4ea6ea6ea0a5d48fc058a513
Weakness classification (CWE)
References
- github.com/haproxy/haproxy/commit/9a6d1fe3f00d86ab4ea6ea6ea0a5d48fc058a513 (Patch, patch)
- www.vulncheck.com/advisories/haproxy-null-pointer-dereference-in-hpack-dht-inse… (Third Party Advisory, third-party-advisory)
Frequently asked questions
- What is CVE-2026-55204?
- CVE-2026-55204 is a high-severity vulnerability in Haproxy, classified under NULL Pointer Dereference. CVSS score: 7.5/10. Published 2026-06-18.
- How severe is CVE-2026-55204?
- High severity. CVSS v3 base score is 7.5 out of 10.