CVE-2026-21388: Mattermost MS Teams plugin doesn't limit the request body size on the /lifecycle webhook endpoint

April 9, 2026 (updated April 29, 2026)

Mattermost Plugins versions <=2.3.1 fail to limit the request body size on the {{/lifecycle}} webhook endpoint which allows an authenticated attacker to cause memory exhaustion and denial of service via sending an oversized JSON payload. Mattermost Advisory ID: MMSA-2026-00610.

References

github.com/advisories/GHSA-x274-8qfc-hrgf
github.com/mattermost/mattermost-plugin-msteams/commit/6fe4d295592ecc8767d67e69286cbeec01be3210
github.com/mattermost/mattermost-plugin-msteams/releases/tag/v2.3.2
mattermost.com/security-updates
nvd.nist.gov/vuln/detail/CVE-2026-21388

Code Behaviors & Features

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