Vulnerability in HAProxy (June 29, 2026)

unknownCVE-2026-55204

A vulnerability has been discovered in HAProxy. It allows an attacker to cause remote denial of service.

CSIRTS triage

vendor: HAProxy product: HAProxy Denial of service

What: A vulnerability allows for remote denial of service in HAProxy.
Who is affected: Users of HAProxy, specifics not detailed in the advisory.
Urgency: Remediation is urgent due to the potential for denial of service attacks.
Action: Update HAProxy to the latest version to mitigate this vulnerability.

AI-assisted analysis generated from the source advisory — verify against the original.

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Details

Source: CERT-FR Avis de sécurité (FR · national-cert · site)
Severity: unknown
Published: 2026-06-29
Exploitation: Not in CISA KEV at last sync
Language: Machine-translated to English — verify against the original

Original advisory: https://www.cert.ssi.gouv.fr/avis/CERTFR-2026-AVI-0814/

Exploitation outlook

EPSS (FIRST.org) estimates each CVE’s probability of exploitation in the next 30 days — here is the CSIRTS.com read on those numbers.

Low exploitation riskCVE-2026-552040.43% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 35% of all scored CVEs.

Referenced CVEs

CVE	CSIRTS overview	External
CVE-2026-55204	coverage & exploitation status	NVD · CVE.org

Same CVEs, other sources

How other CERTs, PSIRTs and databases cover the vulnerabilities in this advisory.

Recent advisories for HAProxy

A cluster of recent advisories against the same product widens the attack surface — attackers routinely chain freshly published CVEs on one product, so review these together.

high[UPDATE] [high] HAProxy: Multiple vulnerabilitiescert-bund · 2026-07-09
highGHSA-h2qv-fj59-j46j: Netty HAProxy: Unbalanced Reference Count in Nested PP2_TYPE_SSL TLV Parsing Leads to Mem…ghsa · 2026-06-11
highCVE-2026-55204: HAProxy - NULL Pointer Dereference in hpack_dht_insert Functionmsrc · 2026-06-09
highCVE-2026-55203: HAProxy - Integer Overflow in FCGI Demux Record Length Fieldmsrc · 2026-06-09