CVE-2026-4635: Persistent notification timing attack causing server denial of service

Published May 22, 2026
·
Updated

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

Affected Software

1 affected component
Mattermost Mattermost=11.6.0, >=11.5.0<=11.5.3, >=11.4.0<=11.4.4, >=10.11.0<=10.11.14

Remediation

Information

Update Mattermost to versions 11.7.0, 11.6.1, 11.5.4, 11.4.5, 10.11.15 or higher.

Event History

May 22, 2026
CVE Published
via MITRE·10:28 AM
Data Sourced
via MITRE·10:28 AM
RemedyDescriptionSeverityWeakness
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Frequently Asked Questions

1

What is the severity of CVE-2026-4635?

CVE-2026-4635 has a medium severity rating of 6.5.

2

What systems are affected by CVE-2026-4635?

CVE-2026-4635 affects Mattermost versions 11.6.x <= 11.6.0, 11.5.x <= 11.5.3, 11.4.x <= 11.4.4, and 10.11.x <= 10.11.14.

3

What kind of attack is described in CVE-2026-4635?

CVE-2026-4635 describes a persistent notification timing attack that can cause server denial of service.

4

How do I fix CVE-2026-4635?

To fix CVE-2026-4635, update Mattermost to versions 11.7.0, 11.6.1, 11.5.4, 11.4.5, 10.11.15 or higher.

5

What is the potential impact of CVE-2026-4635?

The potential impact of CVE-2026-4635 is that an authenticated user can crash the server.

Company

Resources

Contact

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