Mattermost versions 11.6.x <= 11.6.5, 10.11.x <= 10.11.20, 11.8.x <= 11.8.1, 11.7.x <= 11.7.4 fail to limit the number of frames and enforce the file size cap on animated GIF uploads, which allows an authenticated attacker to cause a denial of service via a crafted animated GIF uploaded as a custom emoji.. Mattermost Advisory ID: MMSA-2026-00695
Weakness
The product does not handle or incorrectly handles a compressed input with a very high compression ratio that produces a large output.
Affected Software
| Name | Vendor | Start Version | End Version |
|---|---|---|---|
| Mattermost_server | Mattermost | 10.11.0 (including) | 10.11.21 (excluding) |
| Mattermost_server | Mattermost | 11.6.0 (including) | 11.6.6 (excluding) |
| Mattermost_server | Mattermost | 11.7.0 (including) | 11.7.5 (excluding) |
| Mattermost_server | Mattermost | 11.8.0 (including) | 11.8.2 (excluding) |