Medium severity · published Sep 14, 2026
CVE-2026-86348
MS Calendar plugin: unrecovered handler panics from malformed post-action requests could crash the plugin process
4.3
CVSS
0.4%
EPSS
No
On KEV
Description
Mattermost versions <=11.9 11.0.9 11.4.8 11.7.7 10.22.11.0 fail to recover from handler panics, which allows an authenticated user to crash the plugin via a post-action request with an unexpected field type.. Mattermost Advisory ID: MMSA-2026-00701
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L
Attack vector
Network
Complexity
Low
Privileges
Low
User interaction
None
Confidentiality
None
Integrity
None
Availability
Low
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.4% · higher than 30% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
MA
Mattermost · Mattermost
<=11.9 11.0.9 11.4.8 11.7.7 10.22.11.0 through <=11.9 11.0.9 11.4.8 11.7.7 10.22.11.0 · source: vendor
MS
Mattermost Server · Mattermost
10.11.0 before 10.11.23; 11.7.0 before 11.7.8; 11.8.0 before 11.8.5; 11.9.0 before 11.9.1 · source: NVD
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-86348
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-86348
Vendor Advisory
https://mattermost.com/security-updates
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