CVE-2026-6340: Mattermost doesn't validate 7zip archive structure before processing

May 18, 2026 (updated June 1, 2026)

Mattermost versions 11.5.x <= 11.5.1, 10.11.x <= 10.11.13, 11.4.x <= 11.4.3 fail to validate 7zip archive structure before processing which allows an authenticated attacker to cause server memory exhaustion and denial of service via uploading a specially crafted 7zip file with excessive folder declarations.. Mattermost Advisory ID: MMSA-2026-00573

References

github.com/advisories/GHSA-cjm8-jxpw-g43m
github.com/mattermost/mattermost/commit/fb11968f8798925c7b75711025bc5f991124ba26
mattermost.com/security-updates
nvd.nist.gov/vuln/detail/CVE-2026-6340

Code Behaviors & Features

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