CVE-2026-5755: Denial of service via crafted TIFF file upload
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
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade to a fixed release to a version that resolves this vulnerability.
Patch MMSA-2026-00648 - Upgrade
Upgrade
Mattermostto a version that resolves this vulnerability.Fixed in 11.7.0 - Upgrade
Upgrade
Mattermostto a version that resolves this vulnerability.Fixed in 11.6.1 - Upgrade
Upgrade
Mattermostto a version that resolves this vulnerability.Fixed in 11.5.3 - Upgrade
Upgrade
Mattermostto a version that resolves this vulnerability.Fixed in 11.5.4 - Upgrade
Upgrade
Mattermostto a version that resolves this vulnerability.Fixed in 11.4.5 - Upgrade
Upgrade
Mattermostto a version that resolves this vulnerability.Fixed in 10.11.15
Event History
Frequently Asked Questions
What is the severity of CVE-2026-5755?
CVE-2026-5755 has a medium severity rating of 6.5.
How do I fix CVE-2026-5755?
To fix CVE-2026-5755, you should update Mattermost to version 11.7.0, 11.6.1, 11.5.3, 11.5.4, 11.4.5, 10.11.15 or higher.
What system versions are affected by CVE-2026-5755?
CVE-2026-5755 affects 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, and 10.11.x <= 10.11.14.
What type of attack is CVE-2026-5755 associated with?
CVE-2026-5755 is associated with a denial of service attack via crafted TIFF file uploads.
Who can exploit CVE-2026-5755?
CVE-2026-5755 can be exploited by authenticated users who have file upload or posting permissions.