CVE-2026-10819 PUBLISHED

Mattermost Server Denial of Service via Animated GIF Emoji Upload

Assigner: Mattermost
Reserved: 04.06.2026 Published: 27.07.2026 Updated: 27.07.2026

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

Metrics

CVSS 3.1

CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
CVSS Score: 6.5

Attack Vector	Network	Scope	Unchanged
Attack Complexity	Low	Confidentiality Impact	None
Privileges Required	Low	Integrity Impact	None
User Interaction	None	Availability Impact	High

CVSS 3.1

Product Status

Vendor	Mattermost
Product	Mattermost
Versions	Default: unaffected affected from 11.6.0 to 11.6.5 (incl.) affected from 10.11.0 to 10.11.20 (incl.) affected from 11.8.0 to 11.8.1 (incl.) affected from 11.7.0 to 11.7.4 (incl.) Version 11.9.0 is unaffected Version 11.6.6 is unaffected Version 10.11.21 is unaffected Version 11.8.2 is unaffected Version 11.7.5 is unaffected

Solutions

Update Mattermost to versions 11.9.0, 11.6.6, 10.11.21, 11.8.2, 11.7.5 or higher.

Credits

Adam Korczynski finder

References

MMSA-2026-00695

Problem Types

CWE-409: Improper Handling of Highly Compressed Data (Data Amplification) CWE