CVE-2026-86348 PUBLISHED

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

Assigner: Mattermost
Reserved: 07.09.2026 Published: 14.09.2026 Updated: 14.09.2026

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

Metrics

CVSS 3.1

CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L
CVSS Score: 4.3

Attack Vector	Network	Scope	Unchanged
Attack Complexity	Low	Confidentiality Impact	None
Privileges Required	Low	Integrity Impact	None
User Interaction	None	Availability Impact	Low

CVSS 3.1

Product Status

Vendor	Mattermost
Product	Mattermost
Versions	Default: unaffected affected from <=11.9 11.0.9 11.4.8 11.7.7 10.22.11.0 to <=11.9 11.0.9 11.4.8 11.7.7 10.22.11.0 (incl.) Version 11.10.0 is unaffected Version 11.9.1 is unaffected Version 11.8.5 is unaffected Version 11.7.8 is unaffected Version 10.11.23 is unaffected

Solutions

Update Mattermost to versions 11.10.0, 11.9.1, 11.8.5, 11.7.8, 10.11.23 or higher.

Credits

alimursaliyev finder

References

MMSA-2026-00701

Problem Types

CWE-704: Incorrect Type Conversion or Cast CWE