CVE-2026-5755: Mattermost doesn't validate the TIFF IFD offset in the image header before allocating memory

May 26, 2026 (updated June 29, 2026)

Mattermost versions 11.6.x <= 11.6.0, 11.5.x <= 11.5.2, 11.5.x <= 11.5.3, 11.4.x <= 11.4.4, 10.11.x <= 10.11.14 fail to validate the TIFF IFD offset in the image header before allocating memory, which allows authenticated users with file upload or posting permissions to cause a denial of service (server OOM) via uploading a crafted TIFF file or posting a URL that serves one.. Mattermost Advisory ID: MMSA-2026-00648

References

github.com/advisories/GHSA-37j2-3vv8-cf24
github.com/mattermost/mattermost/commit/d37c2d9d50b50963dabd92153adf7ed52016769a
mattermost.com/security-updates
nvd.nist.gov/vuln/detail/CVE-2026-5755

Code Behaviors & Features

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