CVE-2026-6957 Path traversal in Mattermost
A remote administrator can write arbitrary files to the server via unsanitized filenames in federated shared-channel attachments.
- Exploited in the wild
- Not known
- Login needed
- An administrator
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-6957?
CVE-2026-6957 is a high-severity path traversal vulnerability in Mattermost, published on 27 May 2026. An attacker needs administrator access to exploit it, with no action from the victim.
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
Weakness: CWE-22
Which versions are affected by CVE-2026-6957?
It affects 1 product.
Products include Mattermost Legal Hold.
How do I fix CVE-2026-6957?
No fix has been published for CVE-2026-6957 yet. Limit exposure of the affected software until one is available.
Upgrade, and resolve every user-supplied path against an allowed base folder before opening it. More about Path traversal.
Is CVE-2026-6957 being exploited?
There is no known exploitation of CVE-2026-6957 in the wild and no public exploit code.
Other vulnerabilities in Mattermost
Sources
Also known as GHSA-x7w4-j7hv-94wg.