Mattermost 1.1.5 Arbitrary File Write via Unsanitized fn (CVE-2026-6957)
CVE-2026-6957 Published on May 27, 2026
Path traversal in Mattermost Legal Hold plugin via unsanitized file name from federated peer allows arbitrary file write.
Mattermost Plugins versions <=1.1.5 fail to sanitize filenames received from federated peers before using them to construct export destination paths, which allows an administrator of a remote federated Mattermost server to write files to arbitrary locations within the target server's filestore via a malicious filename delivered through the shared-channel attachment sync protocol. Mattermost Advisory ID: MMSA-2026-00659
Vulnerability Analysis
CVE-2026-6957 can be exploited with network access, and requires user privileges. This vulnerability is consided to have a high level of attack complexity. The potential impact of an exploit of this vulnerability is considered to be very high.
Weakness Type
What is a Directory traversal Vulnerability?
The software uses external input to construct a pathname that is intended to identify a file or directory that is located underneath a restricted parent directory, but the software does not properly neutralize special elements within the pathname that can cause the pathname to resolve to a location that is outside of the restricted directory.
CVE-2026-6957 has been classified to as a Directory traversal vulnerability or weakness.
Products Associated with CVE-2026-6957
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Affected Versions
Mattermost:- Before and including 1.1.5 is affected.
- Version .0 is unaffected.