CVE-2026-10556
🔶 mediumSummary
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
CVSS Score
5.3
Medium
EPSS Score
0.3
Exploit Probability
Published Date
2026-09-14
First Seen: 2026-09-16
📊 Relative Risk Intelligence
This CVE is Lower Risk - more severe than 19.0% of all 358,566 vulnerabilities in our database.
#290,296
Below average severity
Severity Percentile
🎯 CISA SSVC Assessment Updated: Sep 14, 2026
🔍 Exploitation Status
None
No known exploits
⚙️ Automatable
YES
Can be exploited automatically
💥 Technical Impact
Partial
Limited system impact
🏆 Discovered By
kamil-sawicki
SSVC data provided by
CISA
Last Modified
2026-09-16
Source
NVD 🔗
CVSS Vector 3.1
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
CWE IDs (Weakness Types)