CVE-2026-4915
Medium
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
SeverityMedium
CVSS6.5
Exploit probability—
Product
Mattermost Server
PublishedMay 25, 2026
First seenMay 25, 2026
Weakness typeCWE-754CWE-754
How to fix
Update
- mattermost mattermost_server10.11.15, 11.4.5, 11.5.4, 11.6.1 or later
- github.com/mattermost/mattermost-server11.6.1, 11.5.4, 11.4.5, 10.11.15, 10.11.15+incompatible, 11.4.5+incompatible, 11.5.4+incompatible, 11.6.1+incompatible or later
- github.com/mattermost/mattermost/server/v88.0.0-20260407102538-faa7d75b4ea0 or later
Vendor advisories
Affected products
| Product | Affected versions | Fixed in |
|---|---|---|
| mattermost mattermost_server | 10.11.0 ≤ v < 10.11.15, 11.4.0 ≤ v < 11.4.5, 11.5.0 ≤ v < 11.5.4, 11.6.0 ≤ v < 11.6.1 | 10.11.15, 11.4.5, 11.5.4, 11.6.1 |
| github.com/mattermost/mattermost-serverGo | 11.6.0 ≤ v < 11.6.1, 11.5.0 ≤ v < 11.5.4, 11.4.0 ≤ v < 11.4.5, 10.11.0 ≤ v < 10.11.15, 10.11.0+incompatible ≤ v < 10.11.15+incompatible, 11.4.0+incompatible ≤ v < 11.4.5+incompatible, 11.5.0+incompatible ≤ v < 11.5.4+incompatible, 11.6.0+incompatible ≤ v < 11.6.1+incompatible | 11.6.1, 11.5.4, 11.4.5, 10.11.15, 10.11.15+incompatible, 11.4.5+incompatible, 11.5.4+incompatible, 11.6.1+incompatible |
| github.com/mattermost/mattermost/server/v8Go | v < 8.0.0-20260407102538-faa7d75b4ea0 | 8.0.0-20260407102538-faa7d75b4ea0 |
| github.com/mattermost/mattermost-server/v5Go | No range specified | — |
| github.com/mattermost/mattermost-server/v6Go | No range specified | — |
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