CVE-2026-25783

Denial of service via malformed User-Agent header in getBrowserVersion

Published Mar 16, 2026 CVSS 3.1 · 4.3 Medium EPSS < 1% KEV · Not listed
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

Remediation

Vendor Solution

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

Tracking

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Advisories

Source ID Title
Github GHSA Github GHSA GHSA-2v3w-6g35-5f9v Mattermost fails to properly validate User-Agent header tokens
References
History
Type Values Removed Values Added
First Time appeared Mattermost mattermost
Vendors & Products Mattermost mattermost
Type Values Removed Values Added
First Time appeared Mattermost
Mattermost mattermost Server
CPEs cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:*
Vendors & Products Mattermost
Mattermost mattermost Server
Type Values Removed Values Added
Metrics ssvc

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

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'}

Weaknesses

Sources

Status
PUBLISHED
Assigner
Mattermost
Published
Updated
Mar 16, 2026, 1:49 PM
Reserved
Feb 13, 2026, 10:01 AM
Status
Analyzed
Published
Mar 16, 2026, 2:18 PM
Modified
Jun 17, 2026, 10:25 AM