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Vulnerabilities

Vulnerability · CVE-2026-33555

An issue was discovered in HAProxy before 3.3.6.

Published Apr 13, 2026 · catalog updated Jun 29, 2026 · An issue was discovered

Check if you run it

No confirmed exploitation is on record for CVE-2026-33555. EPSS is 0.58%. Act only if a listed version of An issue was discovered is installed.

Gaps on this record

  • The stored product name is a package slug. The name on this page is taken from the title (An issue was discovered).
  • No version range is stored. A customer cannot check an installed version against this record.
  • No vendor fix or required action is stored. Compare the linked advisory before you change production.
Severity
Medium5.8
Known exploitation
Not in CISA/VulnCheck KEV
EPSS
0.58%
Remediation
Advisory link
Affected products
cpe haproxy/haproxy

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.

Are you affected?

Enter the version you run. The result uses only the ranges stored on this record.

The check returns affected, not affected, or incomplete. It does not guess a version that is missing from the record.

  • cpe haproxy/haproxyversion unspecified

How to fix CVE-2026-33555

What to do

Three questions, each answered from this record only. Confirm the vendor advisory before you patch.

Should you patch?

No confirmed exploitation is on record for CVE-2026-33555. EPSS is 0.58%. Act only if a listed version of An issue was discovered is installed.

Which versions are affected?

Affected version ranges are not on this record. Compare the installed version with the linked vendor advisory before you change production.

What should an analyst verify?

CWE-130. EPSS 0.58%. There is no CISA KEV listing. No Exploit-DB or Metasploit reference is linked. Use the source links for the original advisory.

Code

The project this record applies to. Exploit listings stay in References.

Timeline

Detection, updates, and resolution for this record.

  1. Apr 13, 2026 · NIST NVD

    Detected

    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.

  2. Jun 29, 2026 · NIST NVD

    Updated

    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.

Sources

  • CVE.orgVulnerability recordCVE-2026-33555

    Official CVE identifier

    cve.org
  • FIRST EPSSExploitation probabilityCVE-2026-33555

    30-day exploitation probability 0.6%

    first.org
  • NIST NVDVulnerability recordCVE-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 serv

    nvd.nist.gov

References

Freshness

Last verified in this catalog Oct 18, 2026. Significant claims (KEV, EPSS, CVSS, affected ranges) come from the source rows above — open the original publisher for the authoritative advisory.