CVE-2026-6957

medium

Published 2026-05-27 · Modified 2026-06-02

💬 Discuss on Community ✚ Propose mitigation

CVSS v3

4.9

CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:N/I:H/A:N

CVSS v4 NEW

—

not yet in upstream

VIR risk

4.9

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

Predictions

Exploit likelihood

59%

Patch ETA

—

Heuristic predictions, AS-IS, for prioritization only.

Mitigations

No mitigations published for this CVE yet.

The vendor-content worker queues fetches as references arrive (check back in a few minutes). Or — if you've already worked around this in production — publish your fix to the community-verified tier.

✚ Propose a mitigation on Community → Mitigations published via the community go through AI scoring + 2 human reviewers + 7-day silent objection window before landing here with source_tier=community-verified.

Application impact

Vendor	Product	Versions	Fixed
mattermost	legal_hold	`{"endIncluding":"1.1.5"}`

References

https://mattermost.com/security-updates

CWEs

CWE-22

Community-verified mitigations for this CVE will appear above when contributors publish them.

Verify integrity in audit chain (admin only). AS-IS.