Medium severity · published Apr 15, 2026
CVE-2026-3590
Race Condition in Guest Magic Link Authentication Allows Token Reuse
6.5
CVSS
0.2%
EPSS
No
On KEV
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
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Confidentiality
Low
Integrity
Low
Availability
None
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.2% · higher than 4% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
MA
Mattermost · Mattermost
10.11.0 through 10.11.12; 11.5.0 through 11.5.0; 11.4.0 through 11.4.2; 11.3.0 through 11.3.2 · source: vendor
MS
Mattermost Server · Mattermost
10.11.0 before 10.11.13; 11.3.0 before 11.3.3; 11.4.0 before 11.4.3; 11.5.0 before 11.5.1 · source: NVD
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-3590
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-3590
Vendor Advisory
https://mattermost.com/security-updates
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