CVE-2026-25783

Description

Mattermost fails to properly validate User-Agent header tokens in github.com/mattermost/mattermost-server. NOTE: The source advisory for this report contains additional versions that could not be automatically mapped to standard Go module versions. (If this is causing false-positive reports from vulnerability scanners, please suggest an edit to the report.) The additional affected modules and versions are: github.com/mattermost/mattermost-server/v5 before v5.3.2-0.20260129181235-1346cf529aef.

How to fix CVE-2026-25783

To remediate CVE-2026-25783, upgrade the affected package to a fixed version below.

• —upgrade to 5.3.2-0.20260129181235-1346cf529aef or later
• —upgrade to 10.11.11+incompatible or later
• —no fix listed
• —no fix listed
• —upgrade to 8.0.0-20260129181235-1346cf529aef or later
• —upgrade to 8.0.0-20260129181235-1346cf529aef or later

Is CVE-2026-25783 being exploited?

Low — EPSS is 0.1%, meaning exploitation activity has not been observed at scale.

Affected packages (6)

• from 0, < 5.3.2-0.20260129181235-1346cf529aef
• >= 10.11.0-rc1+incompatible, < 10.11.11+incompatible, >= 11.2.0-rc1+incompatible, < 11.2.3+incompatible, >= 11.3.0-rc1+incompatible, < 11.3.1+incompatible
• from 0
• from 0
• from 0, < 8.0.0-20260129181235-1346cf529aef
• from 0, < 8.0.0-20260129181235-1346cf529aef

CVSS scores

References (5)

• ADVISORYgithub.com/advisories/GHSA-2v3w-6g35-5f9v
• ADVISORYnvd.nist.gov/vuln/detail/CVE-2026-25783
• PATCHgithub.com/mattermost/mattermost
• WEBgithub.com/mattermost/mattermost/commit/1346cf529aef0672c39a56ec10d1b8a9c8fb387d
• WEB