CVE-2026-26233: Mattermost doesn't rate limit login requests, allowing DoS

March 25, 2026 (updated April 6, 2026)

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

References

github.com/advisories/GHSA-247x-7qw8-fp98
github.com/mattermost/mattermost
mattermost.com/security-updates
nvd.nist.gov/vuln/detail/CVE-2026-26233

Code Behaviors & Features

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