CVEDB API

Vulnerabilities

Vulnerable Software

Vulnerability Details CVE-2026-10556

Mattermost versions 11.9.x <= 11.9.0, 11.8.x <= 11.8.4, 11.7.x <= 11.7.7, 10.11.x <= 10.11.22 fail to validate null entries in Microsoft Graph webhook notification payloads, which allows an unauthenticated attacker to crash the Microsoft Calendar plugin process and deny calendar integration service to all users on the instance via a crafted {{POST}} request to the public webhook endpoint.. Mattermost Advisory ID: MMSA-2026-00693

Exploit prediction scoring system (EPSS) score

EPSS Score 0.002

EPSS Ranking 14.8%

CVSS Severity

CVSS v3 Score 5.3

References

https://mattermost.com/security-updates

Products affected by CVE-2026-10556

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: 10.11.19

cpe:2.3:a:mattermost:mattermost_server:10.11.19
Mattermost » Mattermost Server » Version: 10.11.2

cpe:2.3:a:mattermost:mattermost_server:10.11.2
Mattermost » Mattermost Server » Version: 10.11.20

cpe:2.3:a:mattermost:mattermost_server:10.11.20
Mattermost » Mattermost Server » Version: 10.11.21

cpe:2.3:a:mattermost:mattermost_server:10.11.21
Mattermost » Mattermost Server » Version: 10.11.22

cpe:2.3:a:mattermost:mattermost_server:10.11.22
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: 11.7.0

cpe:2.3:a:mattermost:mattermost_server:11.7.0
Mattermost » Mattermost Server » Version: 11.7.1

cpe:2.3:a:mattermost:mattermost_server:11.7.1
Mattermost » Mattermost Server » Version: 11.7.2

cpe:2.3:a:mattermost:mattermost_server:11.7.2
Mattermost » Mattermost Server » Version: 11.7.3

cpe:2.3:a:mattermost:mattermost_server:11.7.3
Mattermost » Mattermost Server » Version: 11.7.4

cpe:2.3:a:mattermost:mattermost_server:11.7.4
Mattermost » Mattermost Server » Version: 11.7.5

cpe:2.3:a:mattermost:mattermost_server:11.7.5
Mattermost » Mattermost Server » Version: 11.7.6

cpe:2.3:a:mattermost:mattermost_server:11.7.6
Mattermost » Mattermost Server » Version: 11.7.7

cpe:2.3:a:mattermost:mattermost_server:11.7.7
Mattermost » Mattermost Server » Version: 11.8.0

cpe:2.3:a:mattermost:mattermost_server:11.8.0
Mattermost » Mattermost Server » Version: 11.8.1

cpe:2.3:a:mattermost:mattermost_server:11.8.1
Mattermost » Mattermost Server » Version: 11.8.2

cpe:2.3:a:mattermost:mattermost_server:11.8.2
Mattermost » Mattermost Server » Version: 11.8.3

cpe:2.3:a:mattermost:mattermost_server:11.8.3
Mattermost » Mattermost Server » Version: 11.8.4

cpe:2.3:a:mattermost:mattermost_server:11.8.4

Vulnerabilities

Vulnerable Software

Vulnerability Details CVE-2026-10556

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