How severe is CVE-2026-33555?

CVE-2026-33555 has a CVSS 3.x base score of 4.0, rated medium severity. It is exploitable over network with high attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity low, and availability none.

Is CVE-2026-33555 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (21st percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-33555?

CVE-2026-33555 affects Haproxy. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2026-33555?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

Does CVE-2026-33555 have an EU (EUVD) identifier?

Yes. CVE-2026-33555 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-21997.

When was CVE-2026-33555 published?

CVE-2026-33555 was published on 2026-04-13 and last updated on 2026-06-29.

CVE-2026-33555

CVE-2026-33555 is a medium-severity vulnerability in Haproxy with a CVSS 3.x base score of 4.0. 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-130.

Key facts

Severity: Medium (CVSS 3.x base score 4.0)
EPSS exploit prediction: 0% (21st percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-21997
Weakness: CWE-130
Affected product: Haproxy
Published: 2026-04-13
Last modified: 2026-06-29

Description

An issue was discovered in HAProxy before 3.3.6. The HTTP/3 parser does not check that the received body length matches a previously announced content-length when the stream is closed via a frame with an empty payload. This can cause desynchronization issues with the backend server and could be used for request smuggling. The earliest affected version is 2.6.

Frequently asked questions

What is CVE-2026-33555?: An issue was discovered in HAProxy before 3.3.6. The HTTP/3 parser does not check that the received body length matches a previously announced content-length when the stream is closed via a frame with an empty payload. This can cause desynchronization issues with the backend server and could be used for request smuggling. The earliest affected version is 2.6.
How severe is CVE-2026-33555?: CVE-2026-33555 has a CVSS 3.x base score of 4.0, rated medium severity. It is exploitable over network with high attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity low, and availability none.
Is CVE-2026-33555 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (21st percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-33555?: CVE-2026-33555 affects Haproxy. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2026-33555?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
Does CVE-2026-33555 have an EU (EUVD) identifier?: Yes. CVE-2026-33555 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-21997.
When was CVE-2026-33555 published?: CVE-2026-33555 was published on 2026-04-13 and last updated on 2026-06-29.

References

Affected products (1)

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

More vulnerabilities in Haproxy

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Other CWE-130 vulnerabilities

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CVE-2022-1543 — High (CVSS 8.8): Improper handling of Length parameter in GitHub repository erudika/scoold prior to 1.49.4. When the text size is large…
CVE-2026-3868 — High (CVSS 8.7): An improper handling of the length parameter inconsistency vulnerability has been identified in Moxa’s Secure…
CVE-2026-5367 — High (CVSS 8.6): A flaw was found in OVN (Open Virtual Network). A remote attacker, by sending crafted DHCPv6 (Dynamic Host…
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