CVEDB API

Vulnerabilities

Vulnerable Software

Vulnerability Details CVE-2026-4339

Mattermost versions 10.11.x <= 10.11.18, 11.6.x <= 11.6.3, 11.5.x <= 11.5.6 fail to validate attachment URLs against internal or private IP ranges in the Mattermost Agents plugin MCP server which allows an attacker with access to the MCP server in stdio mode to perform server-side request forgery (SSRF) and exfiltrate data from internal network services via supplying internal URLs as file attachments in post creation requests.. Mattermost Advisory ID: MMSA-2026-00635

Exploit prediction scoring system (EPSS) score

EPSS Score 0.001

EPSS Ranking 1.2%

CVSS Severity

CVSS v3 Score 6.5

References

https://mattermost.com/security-updates

Products affected by CVE-2026-4339

Mattermost » Mattermost Server » Version: 10.11.0

cpe:2.3:a:mattermost:mattermost_server:10.11.0
Mattermost » Mattermost Server » Version: 10.11.1

cpe:2.3:a:mattermost:mattermost_server:10.11.1
Mattermost » Mattermost Server » Version: 10.11.10

cpe:2.3:a:mattermost:mattermost_server:10.11.10
Mattermost » Mattermost Server » Version: 10.11.11

cpe:2.3:a:mattermost:mattermost_server:10.11.11
Mattermost » Mattermost Server » Version: 10.11.12

cpe:2.3:a:mattermost:mattermost_server:10.11.12
Mattermost » Mattermost Server » Version: 10.11.13

cpe:2.3:a:mattermost:mattermost_server:10.11.13
Mattermost » Mattermost Server » Version: 10.11.14

cpe:2.3:a:mattermost:mattermost_server:10.11.14
Mattermost » Mattermost Server » Version: 10.11.15

cpe:2.3:a:mattermost:mattermost_server:10.11.15
Mattermost » Mattermost Server » Version: 10.11.16

cpe:2.3:a:mattermost:mattermost_server:10.11.16
Mattermost » Mattermost Server » Version: 10.11.17

cpe:2.3:a:mattermost:mattermost_server:10.11.17
Mattermost » Mattermost Server » Version: 10.11.18

cpe:2.3:a:mattermost:mattermost_server:10.11.18
Mattermost » Mattermost Server » Version: 10.11.2

cpe:2.3:a:mattermost:mattermost_server:10.11.2
Mattermost » Mattermost Server » Version: 10.11.3

cpe:2.3:a:mattermost:mattermost_server:10.11.3
Mattermost » Mattermost Server » Version: 10.11.4

cpe:2.3:a:mattermost:mattermost_server:10.11.4
Mattermost » Mattermost Server » Version: 10.11.5

cpe:2.3:a:mattermost:mattermost_server:10.11.5
Mattermost » Mattermost Server » Version: 10.11.6

cpe:2.3:a:mattermost:mattermost_server:10.11.6
Mattermost » Mattermost Server » Version: 10.11.7

cpe:2.3:a:mattermost:mattermost_server:10.11.7
Mattermost » Mattermost Server » Version: 10.11.8

cpe:2.3:a:mattermost:mattermost_server:10.11.8
Mattermost » Mattermost Server » Version: 10.11.9

cpe:2.3:a:mattermost:mattermost_server:10.11.9
Mattermost » Mattermost Server » Version: 11.5.0

cpe:2.3:a:mattermost:mattermost_server:11.5.0
Mattermost » Mattermost Server » Version: 11.5.1

cpe:2.3:a:mattermost:mattermost_server:11.5.1
Mattermost » Mattermost Server » Version: 11.5.2

cpe:2.3:a:mattermost:mattermost_server:11.5.2
Mattermost » Mattermost Server » Version: 11.5.3

cpe:2.3:a:mattermost:mattermost_server:11.5.3
Mattermost » Mattermost Server » Version: 11.5.4

cpe:2.3:a:mattermost:mattermost_server:11.5.4
Mattermost » Mattermost Server » Version: 11.5.5

cpe:2.3:a:mattermost:mattermost_server:11.5.5
Mattermost » Mattermost Server » Version: 11.5.6

cpe:2.3:a:mattermost:mattermost_server:11.5.6
Mattermost » Mattermost Server » Version: 11.6.0

cpe:2.3:a:mattermost:mattermost_server:11.6.0
Mattermost » Mattermost Server » Version: 11.6.1

cpe:2.3:a:mattermost:mattermost_server:11.6.1
Mattermost » Mattermost Server » Version: 11.6.2

cpe:2.3:a:mattermost:mattermost_server:11.6.2
Mattermost » Mattermost Server » Version: 11.6.3

cpe:2.3:a:mattermost:mattermost_server:11.6.3

Vulnerabilities

Vulnerable Software

Vulnerability Details CVE-2026-4339

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