CVE-2026-9812: Missing property field ownership validation in Playbooks run property update endpoint

Severity: medium (CVSS 6.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.4% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-09-14 · updated 2026-10-06
Weakness: CWE-639

Description

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 that a property field belongs to the specified run before updating its value which allows an authenticated user with run property-management access to crash the Playbooks plugin via a REST request referencing a property field that belongs to a different run. Mattermost Advisory ID: MMSA-2026-00684

Affected products

Mattermost: from 10.11.0 before 10.11.23; from 11.7.0 before 11.7.8; from 11.8.0 before 11.8.5; from 11.9.0 before 11.9.1 — fixed in 10.11.23, 11.7.8, 11.8.5, 11.9.1

How to fix

Upgrade to a fixed version: Mattermost 10.11.23, 11.7.8, 11.8.5, 11.9.1. Check the vendor advisory for mitigations.

References

https://mattermost.com/security-updates

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