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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

PUBLISHED Reserved 2026-02-13 | Published 2026-03-16 | Updated 2026-03-16 | Assigner Mattermost




MEDIUM: 4.3CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L

Problem types

CWE-1287: Improper Validation of Specified Type of Input

Product status

Default status
unaffected

11.3.0 (semver)
affected

11.2.0 (semver)
affected

10.11.0 (semver)
affected

11.4.0
unaffected

11.3.1
unaffected

11.2.3
unaffected

10.11.11
unaffected

Credits

winfunc finder

References

mattermost.com/security-updates (MMSA-2026-00586) vendor-advisory

cve.org (CVE-2026-25783)

nvd.nist.gov (CVE-2026-25783)

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