Vulnerability · Published May 22, 2026 · Assigned by Mattermost
CVE-2026-4635Persistent notification timing attack causing server denial of service
Medium 6.5
In plain English
A medium-severity race condition in Mattermost from Mattermost. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.2% (higher than 7% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official 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
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Go | github.com/mattermost/mattermost-server | 10.11.15+incompatible, 11.4.5+incompatible, 11.5.4+incompatible, 11.6.1+incompatible | GO-2026-5820 |
| Go | github.com/mattermost/mattermost-server | 11.6.1 | GHSA-pg7c-462j-grxv |
| Go | github.com/mattermost/mattermost-server | 11.5.4 | GHSA-pg7c-462j-grxv |
| Go | github.com/mattermost/mattermost-server | 11.4.5 | GHSA-pg7c-462j-grxv |
| Go | github.com/mattermost/mattermost-server | 10.11.15 | GHSA-pg7c-462j-grxv |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| Mattermost | Mattermost | 11.6.0 – through 11.6.011.5.0 – through 11.5.311.4.0 – through 11.4.410.11.0 – through 10.11.14 |
Weakness: CWE-362 · Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
References
- MMSA-2026-00637 vendor-advisory