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CVE-2026-4635— Persistent notification timing attack causing server 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是美国Mattermost公司的一个开源协作平台。 Mattermost 11.6.0及之前的11.6.x版本、11.5.3及之前的11.5.x版本、11.4.4及之前的11.4.x版本和10.11.14及之前的10.11.x版本存在安全漏洞，该漏洞源于在移除持久通知前未归档频道，可能导致认证用户通过在服务器删除现有持久通知和归档频道之间创建持久通知消息来使服务器崩溃。

CVSS 6.5 · Medium EPSS 0.17% · P7

Possible ATT&CK Techniques 1 AI

T1499 · Endpoint Denial of Service

Affected Version Matrix 9

VendorProduct Version RangeStatus
Mattermost Mattermost 11.6.0≤ 11.6.0 affected
11.5.0≤ 11.5.3 affected
11.4.0≤ 11.4.4 affected
10.11.0≤ 10.11.14 affected
11.7.0 unaffected
11.6.1 unaffected
11.5.4 unaffected
11.4.5 unaffected
… +1 more rows
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I. Basic Information for CVE-2026-4635

Vulnerability Information
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Vulnerability Title
Persistent notification timing attack causing server denial of service
Source: CVE Program / CVE List V5
Vulnerability Description
Mattermost versions 11.6.x <= 11.6.0, 11.5.x <= 11.5.3, 11.4.x <= 11.4.4, 10.11.x <= 10.11.14 fail to archive the channel before removing persistent notifications which allows authenticated user to crash the server via timing the creation of persistent notification message between the server deleting existing persistent notifications and archiving the channel.. Mattermost Advisory ID: MMSA-2026-00637
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:H
Source: CVE Program / CVE List V5
Vulnerability Type
使用共享资源的并发执行不恰当同步问题(竞争条件)
Source: CVE Program / CVE List V5
Vulnerability Title
Mattermost 安全漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Mattermost是美国Mattermost公司的一个开源协作平台。 Mattermost 11.6.0及之前的11.6.x版本、11.5.3及之前的11.5.x版本、11.4.4及之前的11.4.x版本和10.11.14及之前的10.11.x版本存在安全漏洞，该漏洞源于在移除持久通知前未归档频道，可能导致认证用户通过在服务器删除现有持久通知和归档频道之间创建持久通知消息来使服务器崩溃。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
Mattermost Mattermost 11.6.0 ~ 11.6.0 -

II. Public POCs for CVE-2026-4635

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III. Intelligence Information for CVE-2026-4635

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Same Patch Batch · Mattermost · 2026-05-22 · 8 CVEs total

CVE-2026-5740 7.5 HIGH Unauthenticated WebSocket binary frame causes denial of service in Mattermost Server
CVE-2026-5755 6.5 MEDIUM Denial of service via crafted TIFF file upload
CVE-2026-3473 5.9 MEDIUM Improper file ownership validation in the Boards API allows unauthorised file access
CVE-2026-28735 5.4 MEDIUM GitHub OAuth Scope Validation
CVE-2026-5308 4.9 MEDIUM Missing request body size limits on Zoom plugin HTTP endpoints
CVE-2026-4646 4.3 MEDIUM Insufficient input validation in GitHub plugin API causes denial of service
CVE-2026-3636 4.3 MEDIUM Sanitize team member data returned by API

IV. Related Vulnerabilities

Same product: Mattermost
Same vendor: Mattermost
Same weakness: CWE-362

V. Comments for CVE-2026-4635

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