Denial of Service Vulnerability in Mattermost by Mattermost
CVE-2026-5755

6.5MEDIUM

Key Information:

Vendor

Mattermost
Status
Mattermost
Vendor
CVE Published:
22 May 2026

What is CVE-2026-5755?

A vulnerability exists in certain versions of Mattermost due to improper validation of the TIFF IFD offset in the image headers, which can lead to a denial of service condition. Authenticated users who have file upload or posting permissions can exploit this flaw by uploading a specially crafted TIFF file or sharing a URL that serves such a file. This exploitation can result in excessive memory allocation, causing the server to run out of memory and become unresponsive.

Affected Version(s)

Mattermost 11.6.0

Mattermost 11.5.0 <= 11.5.2

Mattermost 11.5.0 <= 11.5.3

References

https://mattermost.com/security-updates
vendor-advisory

CVSS V3.1

Score:
6.5
Severity:
MEDIUM
Confidentiality:
None
Integrity:
None
Availability:
None
Attack Vector:
Network
Attack Complexity:
Low
Privileges Required:
Low
User Interaction:
None
Scope:
Unchanged

Timeline

  • Vulnerability published

  • Vulnerability Reserved

Credit

ZephrFish
.