Mattermost versions 11.3.x <= 11.3.0, 11.2.x <= 11.2.2, 10.11.x <= 10.11.10 fail to properly validate User-Agent header tokens which allows an authenticated attacker to cause a request panic via a specially crafted User-Agent header. Mattermost Advisory ID: MMSA-2026-00586

Project Subscriptions

No data.

Advisories
Source ID Title
Github GHSA Github GHSA GHSA-2v3w-6g35-5f9v Mattermost fails to properly validate User-Agent header tokens
Fixes

Solution

Update Mattermost to versions 11.4.0, 11.3.1, 11.2.3, 10.11.11 or higher.


Workaround

No workaround given by the vendor.

References
History

Mon, 16 Mar 2026 14:15:00 +0000

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}


Mon, 16 Mar 2026 12:15:00 +0000

Type Values Removed Values Added
Description Mattermost versions 11.3.x <= 11.3.0, 11.2.x <= 11.2.2, 10.11.x <= 10.11.10 fail to properly validate User-Agent header tokens which allows an authenticated attacker to cause a request panic via a specially crafted User-Agent header. Mattermost Advisory ID: MMSA-2026-00586
Title Denial of service via malformed User-Agent header in getBrowserVersion
Weaknesses CWE-1287
References
Metrics cvssV3_1

{'score': 4.3, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L'}


Projects

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cve-icon MITRE

Status: PUBLISHED

Assigner: Mattermost

Published:

Updated: 2026-03-16T13:49:55.332Z

Reserved: 2026-02-13T10:01:31.949Z

Link: CVE-2026-25783

cve-icon Vulnrichment

Updated: 2026-03-16T13:43:39.912Z

cve-icon NVD

Status : Awaiting Analysis

Published: 2026-03-16T14:18:23.593

Modified: 2026-03-16T14:53:07.390

Link: CVE-2026-25783

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

No data.

Weaknesses