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CVE-2026-95666— Unbounded post ID array in the bulk reactions endpoint allows denial of service

Quick assessment

Affected
Mattermost Mattermost
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

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 crafte

CVSS 4.3 · Medium

Affected Version Matrix 9

VendorProduct Version RangeStatus
Mattermost Mattermost 11.9.0≤ 11.9.1 affected
11.8.0≤ 11.8.5 affected
11.7.0≤ 11.7.10 affected
11.10.0≤ 11.10.1 affected
11.11.0 unaffected
11.9.2 unaffected
11.8.6 unaffected
11.7.11 unaffected
… +1 more rows
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I. Basic Information for CVE-2026-95666

Vulnerability Information

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Vulnerability Title
Unbounded post ID array in the bulk reactions endpoint allows denial of service
Source: CVE Program / CVE List V5
Vulnerability 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
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L
Source: CVE Program / CVE List V5
Vulnerability Type
不加限制或调节的资源分配
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
Mattermost Mattermost 11.9.0 ~ 11.9.1 -

II. Public POCs for CVE-2026-95666

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III. Intelligence Information for CVE-2026-95666

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Same Patch Batch · Mattermost · 2026-09-22 · 3 CVEs total

CVE-2026-96260 6.5 MEDIUM Mattermost server missing request body size limit on plugin routes allows denial of servic
CVE-2026-96259 5.5 MEDIUM Mattermost server-side request forgery via OAuth endpoints configurable by a System Admini

IV. Related Vulnerabilities

Same product: Mattermost
Same vendor: Mattermost
Same weakness: CWE-770

V. Comments for CVE-2026-95666

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