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Vulnerability record · CVE-2026-55204 · published 18 June 2026

CVE-2026-55204: Haproxy null pointer dereference vulnerability

Haproxy · Haproxy

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.

8.7 CVSS 4.0 High EPSS 0.48% · top 60.8% CWE-476 · NULL pointer dereference
8.7CVSS 4.0 base score
0.48%EPSS exploitation probability, 30 days
NoNot in CISA KEV
1Affected product versions listed by NVD
2References
14 Jul 2026Last modified by NVD

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.

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:

Affected products

1 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://github.com/haproxy/haproxy/commit/9a6d1fe3f00d86ab4ea6ea6ea0a5d48fc058a513 Patch
https://www.vulncheck.com/advisories/haproxy-null-pointer-dereference-in-hpack-dht-insert-function Third Party Advisory

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Related vulnerabilities

Same products first, then exploited flaws of the same weakness class.

9.8CVE-2019-19330Haproxy injection vulnerabilityThe HTTP/2 implementation in HAProxy before 2.0.10 mishandles headers, as demonstrated by carriage return (CR, ASCII 0xd), line feed (LF, ASCII 0xa),…EPSS 4.0%9.1CVE-2023-25725Haproxy http request smuggling vulnerabilityHAProxy before 2.7.3 may allow a bypass of access control because HTTP/1 headers are inadvertently lost in some situations, aka "request smuggling." …EPSS 5.4%9.0CVE-2026-55203Haproxy integer overflow vulnerabilityHAProxy through 3.4.0, fixed in commit 5985276, contains an integer overflow vulnerability in the fcgi_conn structure's drl field that allows buffer …EPSS 0.58%8.8CVE-2020-11100HAProxy HPACK decoder heap out-of-bounds writeThe HPACK decoder in HAProxy 1.8 through 2.x before 2.1.4 contains an out-of-bounds write in hpack_dht_insert in hpack-tbl.c. A crafted HTTP/2 reques…EPSS 61%analysed8.2CVE-2023-45539Haproxy vulnerabilityHAProxy before 2.8.2 accepts # as part of the URI component, which might allow remote attackers to obtain sensitive information or have unspecified o…EPSS 1.5%7.5CVE-2025-11230Haproxy aloha appliance vulnerabilityInefficient algorithm complexity in mjson in HAProxy allows remote attackers to cause a denial of service via specially crafted JSON requests.EPSS 0.69%7.5CVE-2024-45506Haproxy vulnerabilityHAProxy 2.9.x before 2.9.10, 3.0.x before 3.0.4, and 3.1.x through 3.1-dev6 allows a remote denial of service for HTTP/2 zero-copy forwarding (h2_sen…EPSS 1.2%7.5CVE-2023-0836Haproxy information exposure vulnerabilityAn information leak vulnerability was discovered in HAProxy 2.1, 2.2 before 2.2.27, 2.3, 2.4 before 2.4.21, 2.5 before 2.5.11, 2.6 before 2.6.8, 2.7 …EPSS 1.2%

Source: NIST National Vulnerability Database (record CVE-2026-55204), CISA KEV, FIRST EPSS (scores of 2026-09-26). This page is refreshed as NVD updates the record.