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🛡️ CVE-2026-33555 on Ubuntu — haproxy

⚪ Unknown ✅ No Known Exploit OSV
N/A
CVSS Score
0 Low4 Medium7 High9 Critical10

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.

Distribution advisory

This page covers CVE-2026-33555 as tracked by Ubuntu, for the package haproxy. The fix is available in version 3.2.9-1ubuntu2.1; earlier versions remain affected.

How this vulnerability can be exploited

This issue can be reached over the network, attack complexity is low, an attacker needs no privileges on the target. No user interaction is required. The scope is changed, meaning a successful attack can affect components beyond the vulnerable one. Rated impact: confidentiality none, integrity low, availability none.

CVSS metrics in full

The score comes from this vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:N

  • Attack vector: Network — reachable from anywhere that can route to the service.
  • Attack complexity: Low — the attack works reliably, with no preparation.
  • Privileges required: None — an unauthenticated stranger can try it.
  • User interaction: None — nobody has to be tricked into anything.
  • Scope: Changed — a successful attack reaches components beyond the vulnerable one.
  • Confidentiality impact: None.
  • Integrity impact: Low — limited, and the attacker does not choose what is affected.
  • Availability impact: None.

Weakness class

UBUNTU-CVE-2026-33555 is classified as CWE-130: Improper Handling of Length Parameter Inconsistency. The product parses a formatted message or structure, but it does not handle or incorrectly handles a length field that is inconsistent with the actual length of the associated data.

Affected software

UBUNTU-CVE-2026-33555 is recorded against 1 package.

  • haproxy (fixed in 3.2.9-1ubuntu2.1)

Timeline and source

Published on 13 April 2026 and last revised on 30 June 2026. No public exploit is currently recorded for this entry. Record sourced from OSV.

References

ubuntu.com (Report)
www.cve.org (Report)
www.haproxy.com (Report)
www.mail-archive.com (Report)
ubuntu.com (Advisory)

Other advisories for this package

haproxy has other advisories on record. If you are patching this one, these are worth checking on the same host:

Same weakness in other software

These advisories are the same class of weakness (CWE-130: Improper Handling of Length Parameter Inconsistency) in other software:

CVE-2026-33555 on other distributions

Each distribution ships its own build and its own fixed version. Pick the one you run:

Details

Severity Unknown
CVSS Score N/A
CVSS Vector CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:N
CWE N/A
Public Exploit ✅ No
Source OSV
Published 2026-04-13
Updated 2026-08-20
Modified 2026-06-30
Fix URL N/A

Affected Packages

Software From version Fixed in
haproxy — 3.2.9-1ubuntu2.1

Similar Threats

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