CVE-2026-6342

medium

Published 2026-05-18 · Modified 2026-05-29

💬 Discuss on Community ✚ Propose mitigation

CVSS v3

4.3

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

CVSS v4 NEW

—

not yet in upstream

VIR risk

4.3

Description

Mattermost Plugins versions <=11.5 11.1.5 10.13.11 11.3.4.0 fail to appropriately check for valid namespaces which allows plugin users to create subscriptions to groups that were not whitelisted via creating groups that share the same prefix as a whitelisted group. Mattermost Advisory ID: MMSA-2026-00601

Predictions

Exploit likelihood

53%

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
mattermost	mattermost_server	`{"startIncluding":"10.13.0","endIncluding":"10.13.11"}`
mattermost	mattermost_server	`{"startIncluding":"11.1.0","endIncluding":"11.1.5"}`
mattermost	mattermost_server	`{"startIncluding":"11.3.0","endIncluding":"11.3.4"}`

References

https://mattermost.com/security-updates

CWEs

CWE-863

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

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