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

No CVSS v4.0

Attack Vector Network

Attack Complexity Low

Privileges Required Low

Scope Unchanged

Confidentiality Impact None

Integrity Impact None

Availability Impact High

User Interaction None

No CVSS v3.0

No CVSS v2

This CVE is not in the KEV list.

No EPSS score available.

Exploitation none

Automatable no

Technical Impact partial

Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).

Vendor Product Default status Versions
Mattermost Mattermost unaffected
Version Status Constraints
11.6.0 affected ≤ 11.6.5
10.11.0 affected ≤ 10.11.20
11.8.0 affected ≤ 11.8.1
11.7.0 affected ≤ 11.7.4
11.9.0 unaffected —
11.6.6 unaffected —
10.11.21 unaffected —
11.8.2 unaffected —
11.7.5 unaffected —

No data.

No data.

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Vendors Products
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Project Subscriptions

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Advisories

No advisories yet.

Fixes

Solution

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

Workaround

No workaround given by the vendor.

References
Link Providers
https://mattermost.com/security-updates cve-icon
History

Mon, 27 Jul 2026 15:45:00 +0000

Type Values Removed Values Added
First Time appeared Mattermost
Mattermost mattermost
Vendors & Products Mattermost
Mattermost mattermost

Mon, 27 Jul 2026 15:30:00 +0000

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}

Mon, 27 Jul 2026 14:30:00 +0000

Type Values Removed Values Added
Description 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
Title Mattermost Server Denial of Service via Animated GIF Emoji Upload
Weaknesses CWE-409
References
Metrics cvssV3_1

{'score': 6.5, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H'}

Projects

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cve-icon MITRE

Status: PUBLISHED

Assigner: Mattermost

Published:

Updated: 2026-07-27T15:05:28.394Z

Reserved: 2026-06-04T07:34:33.428Z

Link: CVE-2026-10819

cve-icon Vulnrichment

Updated: 2026-07-27T15:05:23.347Z

cve-icon NVD

No data.

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

Updated: 2026-07-27T15:22:43Z

Weaknesses