CVE-2026-4635 PUBLISHED

Persistent notification timing attack causing server denial of service

Assigner: Mattermost
Reserved: 23.03.2026 Published: 22.05.2026 Updated: 22.05.2026

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

Metrics

CVSS 3.1

CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
CVSS Score: 6.5

Attack Vector	Network	Scope	Unchanged
Attack Complexity	Low	Confidentiality Impact	None
Privileges Required	Low	Integrity Impact	None
User Interaction	None	Availability Impact	High

CVSS 3.1

Product Status

Vendor	Mattermost
Product	Mattermost
Versions	Default: unaffected affected from 11.6.0 to 11.6.0 (incl.) affected from 11.5.0 to 11.5.3 (incl.) affected from 11.4.0 to 11.4.4 (incl.) affected from 10.11.0 to 10.11.14 (incl.) Version 11.7.0 is unaffected Version 11.6.1 is unaffected Version 11.5.4 is unaffected Version 11.4.5 is unaffected Version 10.11.15 is unaffected

Solutions

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

Credits

daw10 finder

References

MMSA-2026-00637

Problem Types

CWE-362: Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition') CWE