CVE-2026-4915

medium

Published 2026-05-25 · Modified 2026-06-01

💬 Discuss on Community ✚ Propose mitigation

CVSS v3

6.5

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

CVSS v4 NEW

—

not yet in upstream

VIR risk

6.5

Description

Mattermost versions 11.6.x <= 11.6.0, 11.5.x <= 11.5.3, 11.4.x <= 11.4.4, 10.11.x <= 10.11.14 fail to filter nil elements from outgoing webhook attachment payloads before processing, which allows an authenticated user to cause a denial of service (server process termination) via a crafted webhook callback response containing a null attachment entry.. Mattermost Advisory ID: MMSA-2026-00641

Predictions

Exploit likelihood

75%

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	mattermost_server	`{"startIncluding":"10.11.0","endExcluding":"10.11.15"}`	`10.11.15`
mattermost	mattermost_server	`{"startIncluding":"11.4.0","endExcluding":"11.4.5"}`	`11.4.5`
mattermost	mattermost_server	`{"startIncluding":"11.5.0","endExcluding":"11.5.4"}`	`11.5.4`
mattermost	mattermost_server	`{"startIncluding":"11.6.0","endExcluding":"11.6.1"}`	`11.6.1`

References

https://mattermost.com/security-updates

CWEs

CWE-754

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

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