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Description

Mattermost versions 11.4.x <= 11.4.0, 11.3.x <= 11.3.1, 11.2.x <= 11.2.3, 10.11.x <= 10.11.11 fail to rate limit login requests which allows unauthenticated remote attackers to cause denial of service (server crash and restart) via HTTP/2 single packet attack with 100+ parallel login requests.. Mattermost Advisory ID: MMSA-2025-00566

PUBLISHED Reserved 2026-02-23 | Published 2026-03-25 | Updated 2026-03-27 | 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-400 Uncontrolled Resource Consumption

Product status

Default status
unaffected

11.4.0 (semver)
affected

11.3.0 (semver)
affected

11.2.0 (semver)
affected

10.11.0 (semver)
affected

11.5.0
unaffected

11.4.1
unaffected

11.3.2
unaffected

11.2.4
unaffected

10.11.12
unaffected

Credits

Axel Larsson & Jakob Ristner finder

References

mattermost.com/security-updates (MMSA-2025-00566) vendor-advisory

cve.org (CVE-2026-26233)

nvd.nist.gov (CVE-2026-26233)

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