CVE-2026-86348: MS Calendar plugin: unrecovered handler panics from malformed post-action requests could crash the plugin process

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