HAProxy up to 3.3.5 HTTP3 Parser length parameter

CVSS Meta Temp Score
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CTI Interest Score
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3.8$0-$5k0.86

Summaryinfo

A vulnerability classified as problematic was found in HAProxy up to 3.3.5. This issue affects some unknown processing of the component HTTP3 Parser. Executing a manipulation can lead to length parameter. This vulnerability is handled as CVE-2026-33555. The attack can be executed remotely. There is not any exploit available. Upgrading the affected component is advised.

Detailsinfo

A vulnerability has been found in HAProxy up to 3.3.5 and classified as problematic. This vulnerability affects an unknown function of the component HTTP3 Parser. The manipulation with an unknown input leads to a length parameter vulnerability. The CWE definition for the vulnerability is CWE-130. 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. As an impact it is known to affect integrity. CVE summarizes:

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.

This vulnerability was named CVE-2026-33555 since 03/22/2026. The exploitation appears to be difficult. The attack can be initiated remotely. No form of authentication is required for a successful exploitation. There are neither technical details nor an exploit publicly available.

Upgrading to version 3.3.6 eliminates this vulnerability. The upgrade is hosted for download at haproxy.com. Applying the patch 05a295441c621089ffa4318daf0dbca2dd756a84 is able to eliminate this problem. The bugfix is ready for download at github.com. The best possible mitigation is suggested to be upgrading to the latest version.

Once again VulDB remains the best source for vulnerability data.

Productinfo

Type

Name

Version

License

Website

CPE 2.3info

CPE 2.2info

CVSSv4info

VulDB Vector: 🔒
VulDB Reliability: 🔍

CVSSv3info

VulDB Meta Base Score: 3.8
VulDB Meta Temp Score: 3.8

VulDB Base Score: 3.7
VulDB Temp Score: 3.6
VulDB Vector: 🔒
VulDB Reliability: 🔍

CNA Base Score: 4.0
CNA Vector (MITRE): 🔒

CVSSv2info

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VectorComplexityAuthenticationConfidentialityIntegrityAvailability
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VulDB Base Score: 🔒
VulDB Temp Score: 🔒
VulDB Reliability: 🔍

Exploitinginfo

Class: Length parameter
CWE: CWE-130 / CWE-119
CAPEC: 🔒
ATT&CK: 🔒

Physical: No
Local: No
Remote: Yes

Availability: 🔒
Status: Not defined

EPSS Score: 🔒
EPSS Percentile: 🔒

Price Prediction: 🔍
Current Price Estimation: 🔒

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Threat Intelligenceinfo

Interest: 🔍
Active Actors: 🔍
Active APT Groups: 🔍

Countermeasuresinfo

Recommended: Upgrade
Status: 🔍

0-Day Time: 🔒

Upgrade: HAProxy 3.3.6
Patch: 05a295441c621089ffa4318daf0dbca2dd756a84

Timelineinfo

03/22/2026 CVE reserved
04/13/2026 +21 days Advisory disclosed
04/13/2026 +0 days VulDB entry created
04/13/2026 +0 days VulDB entry last update

Sourcesinfo

Product: github.com

Status: Confirmed

CVE: CVE-2026-33555 (🔒)
GCVE (CVE): GCVE-0-2026-33555
GCVE (VulDB): GCVE-100-357196

Entryinfo

Created: 04/13/2026 19:43
Changes: 04/13/2026 19:43 (65)
Complete: 🔍
Cache ID: 216::103

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