Vulnerability · Published May 27, 2026 · Assigned by Mattermost

CVE-2026-6957Path traversal in Mattermost Legal Hold plugin via unsanitized file name from federated peer allows arbitrary file write.

High 8.0

In plain English

A high-severity path traversal in Mattermost from Mattermost. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 22% of all known vulnerabilities).

Severity (CVSS 3.1)8.0High

Exploit odds (30 days)0.3%top 77.7% of all CVEs

Exploited in the wildNo reportsCISA SSVC: none

Attack toolingNoneno public tooling known

Official description

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

Affected products (as reported)

Vendor	Product	Versions
Mattermost	Mattermost	0 – through 1.1.5

Weakness: CWE-22 · Vector: CVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:C/C:H/I:H/A:H

References

MMSA-2026-00659 vendor-advisory