Cyber Resilience

CVE-2026-55204

HighPublic PoCUpdated

Published: 18 June 2026

Published
18 June 2026
Modified
26 June 2026
KEV Added
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Patch
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CVSS Score v4 8.7 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:X/V:X/RE:X/U:X
EPSS Score 0.0043 34.6th percentile
Risk Priority 55 floored blend · peak EPSS

Summary

CVE-2026-55204 is a high-severity NULL Pointer Dereference (CWE-476) vulnerability in Haproxy Haproxy. Its CVSS base score is 8.7 (High).

Operationally, exploitation aligns with the MITRE ATT&CK technique Application or System Exploitation (T1499.004); ranked at the 34.6th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog; a public proof-of-concept is referenced.

OWASP Top 10 for Web (2025)

A10:2025 Mishandling of Exceptional Conditions

EU & UK References

Vulnerability details

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…

more

under memory pressure to dereference a NULL pointer and crash HAProxy worker processes, causing denial of service.

CWE(s)
CWE-476

Related Threats

MITRE ATT&CK Enterprise TechniquesAI

T1499.004 Application or System Exploitation Impact
Adversaries may exploit software vulnerabilities that can cause an application or system to crash and deny availability to users.
attack.mitre.org →
Why these techniques?

Null pointer dereference under memory pressure enables direct application crash and DoS via exploitation of HAProxy.

Confidence: HIGH · MITRE ATT&CK Enterprise v19.0

Affected Assets

haproxy
haproxy
≤ 3.4.0

Mitigating Controls

No mitigating controls mapped yet. The per-CVE control annotator has not reached this CVE.

References