CVE-2026-26233

Denial of Service via HTTP/2 single packet attack on login endpoint

State: Published
Severity: 4.3 Medium
Published: Mar 25, 2026
Updated: Mar 27, 2026
Reserved: Feb 23, 2026

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

Scores

CVSS	Score	Vector	Source
3.1	4.3 Medium	CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L	Mattermost

Weaknesses

CWE-400 Uncontrolled Resource Consumption

Affected Products

Product	Versions
MattermostMattermost	11.4.0 through 11.4.0Affected 11.3.0 through 11.3.1Affected 11.2.0 through 11.2.3Affected 10.11.0 through 10.11.11Affected 11.5.0Not affected 11.4.1Not affected 11.3.2Not affected 11.2.4Not affected 10.11.12Not affected

References

MMSA-2025-00566vendor-advisory

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