Home/CVE/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 sin
CVE

CVE-2026-3590

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 sin

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.

MEDIUM · CVSS 6.5 EPSS 0.00038
Schedule remediation
  • SSVC automatable: yes - attacks can be scripted at scale
Sigma rules0 YARA rules0
⬡

Weakness Classification

CWE-367Time-of-check Time-of-use (TOCTOU) Race Condition
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Affected Products & Versions

4
mattermost server>= 10.11.0 and < 10.11.13
mattermost server>= 11.3.0 and < 11.3.3
mattermost server>= 11.4.0 and < 11.4.3
mattermost server>= 11.5.0 and < 11.5.1
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Affected Packages

2
Language-ecosystem packages (from OSV) tied to this CVE, with the version that fixes it - the dependency-level detail NVD doesn’t carry.
Go github.com/mattermost/mattermost-server MODERATE fixed in 10.11.13
Go github.com/mattermost/mattermost/server/v8 MODERATE fixed in 8.0.0-20250723052842-4cb8d8940332
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Scoring & Timeline

6.5
MEDIUM · CVSS v3.1 · responsibledisclosure@mattermost.com
View on NVD
Attack Vector
Network Adjacent Local Physical
Attack Complexity
Low High
Privileges Required
None Low High
User Interaction
None Required
Scope
Unchanged Changed
Confidentiality
None Low High
Integrity
None Low High
Availability
None Low High
Published to NVD15 Apr 2026 · 12:16 PM
CVSS VectorCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N
SSVC triage · cisa-vulnrichment
Exploitation
none
Automatable
yes
Technical impact
partial
SSVC asks the questions that actually drive patch urgency: is it being exploited, can attacks be automated, and how total is the impact.
🔗

References & Sources

1
Source URLs (vendor pages, mailing lists, write-ups). Exploit/PoC links are in their own section above to avoid duplication.
https://mattermost.com/security-updatesVendor Advisory
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