How severe is CVE-2026-55204?

CVE-2026-55204 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.

Is CVE-2026-55204 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (35th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-55204?

CVE-2026-55204 affects Haproxy. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2026-55204?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

Does CVE-2026-55204 have an EU (EUVD) identifier?

Yes. CVE-2026-55204 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-37906.

When was CVE-2026-55204 published?

CVE-2026-55204 was published on 2026-06-18 and last updated on 2026-06-26.

CVE-2026-55204

CVE-2026-55204 is a high-severity vulnerability in Haproxy with a CVSS 3.x base score of 7.5. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-476.

Key facts

Severity: High (CVSS 3.x base score 7.5)
CVSS v4: 8.7
EPSS exploit prediction: 0% (35th percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-37906
Weakness: CWE-476
Affected product: Haproxy
Published: 2026-06-18
Last modified: 2026-06-26

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.

Frequently asked questions

What is 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.
How severe is CVE-2026-55204?: CVE-2026-55204 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.
Is CVE-2026-55204 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (35th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-55204?: CVE-2026-55204 affects Haproxy. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2026-55204?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
Does CVE-2026-55204 have an EU (EUVD) identifier?: Yes. CVE-2026-55204 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-37906.
When was CVE-2026-55204 published?: CVE-2026-55204 was published on 2026-06-18 and last updated on 2026-06-26.

References

Affected products (1)

cpe:2.3:a:haproxy:haproxy:*:*:*:*:*:*:*:*

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