Vulnerability · Published Apr 15, 2026 · Assigned by Mattermost
CVE-2026-3590Race Condition in Guest Magic Link Authentication Allows Token Reuse
Medium 6.5
In plain English
A medium-severity security flaw 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 4% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official description
Mattermost versions 10.11.x <= 10.11.12, 11.5.x <= 11.5.0, 11.4.x <= 11.4.2, 11.3.x <= 11.3.2 fail to enforce atomic single-use consumption of guest magic link tokens, which allows an attacker with access to a valid magic link to establish multiple independent authenticated sessions via concurrent requests.. Mattermost Advisory ID: MMSA-2026-00624
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Go | github.com/mattermost/mattermost-server | 11.4.3 | GHSA-mh4x-rmrx-3hp4 |
| Go | github.com/mattermost/mattermost-server | 10.11.13 | GHSA-mh4x-rmrx-3hp4 |
| Go | github.com/mattermost/mattermost-server | 11.5.0 | GHSA-mh4x-rmrx-3hp4 |
| Go | github.com/mattermost/mattermost-server | 11.3.3 | GHSA-mh4x-rmrx-3hp4 |
| Go | github.com/mattermost/mattermost-server | 10.11.13+incompatible, 11.3.3+incompatible, 11.4.3+incompatible, 11.5.0+incompatible | GO-2026-5507 |
| Go | github.com/mattermost/mattermost-server/v5 | no fix listed | GO-2026-5507 |
| Go | github.com/mattermost/mattermost-server/v6 | no fix listed | GO-2026-5507 |
| Go | github.com/mattermost/mattermost/server/v8 | 8.0.0-20250723052842-4cb8d8940332 | GO-2026-5507 |
| Go | github.com/mattermost/mattermost/server/v8 | 8.0.0-20250723052842-4cb8d8940332 | GHSA-mh4x-rmrx-3hp4 |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| Mattermost | Mattermost | 10.11.0 – through 10.11.1211.5.0 – through 11.5.011.4.0 – through 11.4.211.3.0 – through 11.3.2 |
Weakness: CWE-367 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N
References
- MMSA-2026-00624 vendor-advisory