Mattermost versions 11.9.x <= 11.9.1, 11.8.x <= 11.8.5, 11.7.x <= 11.7.10, 11.10.x <= 11.10.1 fail to limit the length of the post ID array accepted by the bulk reactions endpoint which allows an authenticated user to cause excessive database load via a crafted request to {{POST /api/v4/posts/ids/reactions}}.. Mattermost Advisory ID: MMSA-2026-00771

No CVSS v4.0

Attack Vector Network

Attack Complexity Low

Privileges Required Low

Scope Unchanged

Confidentiality Impact None

Integrity Impact None

Availability Impact Low

User Interaction None

No CVSS v3.0

No CVSS v2

This CVE is not in the KEV list.

The EPSS score is 0.00367.

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
11.9.0 affected ≤ 11.9.1
11.8.0 affected ≤ 11.8.5
11.7.0 affected ≤ 11.7.10
11.10.0 affected ≤ 11.10.1
11.11.0 unaffected —
11.9.2 unaffected —
11.8.6 unaffected —
11.7.11 unaffected —
11.10.2 unaffected —

Configuration 1 [-]

OR cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:*
cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:*
cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:*
cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:*

No data.

OpenCVE Enrichment is a feature of OpenCVE that uses AI to automatically link vendors and products to CVEs. Learn more on GitHub.

Vendors Products
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Project Subscriptions

Vendors Products
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Advisories

No advisories yet.

Fixes

Solution

Update Mattermost to versions 11.11.0, 11.9.2, 11.8.6, 11.7.11, 11.10.2 or higher.

Workaround

No workaround given by the vendor.

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

Wed, 07 Oct 2026 17:00:00 +0000

Type Values Removed Values Added
First Time appeared Mattermost mattermost Server
CPEs cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:*
Vendors & Products Mattermost mattermost Server

Thu, 24 Sep 2026 04:30:00 +0000

Type Values Removed Values Added
Metrics ssvc

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

Tue, 22 Sep 2026 16:30:00 +0000

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

Tue, 22 Sep 2026 13:30:00 +0000

Type Values Removed Values Added
Description Mattermost versions 11.9.x <= 11.9.1, 11.8.x <= 11.8.5, 11.7.x <= 11.7.10, 11.10.x <= 11.10.1 fail to limit the length of the post ID array accepted by the bulk reactions endpoint which allows an authenticated user to cause excessive database load via a crafted request to {{POST /api/v4/posts/ids/reactions}}.. Mattermost Advisory ID: MMSA-2026-00771
Title Unbounded post ID array in the bulk reactions endpoint allows denial of service
Weaknesses CWE-770
References
Metrics cvssV3_1

{'score': 4.3, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L'}

Projects

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cve-icon MITRE

Status: PUBLISHED

Assigner: Mattermost

Published:

Updated: 2026-09-22T13:57:00.428Z

Reserved: 2026-09-22T13:09:02.237Z

Link: CVE-2026-95666

cve-icon Vulnrichment

Updated: 2026-09-22T13:55:09.639Z

cve-icon NVD

Status : Analyzed

Published: 2026-09-22T14:17:21.437

Modified: 2026-10-07T16:48:51.163

Link: CVE-2026-95666

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

Updated: 2026-09-22T17:00:12Z

Weaknesses