CVE-2025-35965: DoS in Mattermost Playbooks via Excessive Task Actions

Severity: high (CVSS 7.5 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: 2025-04-24 · updated 2026-06-17
Weakness: CWE-770

Description

Mattermost versions 10.4.x <= 10.4.2, 10.5.x <= 10.5.0, 9.11.x <= 9.11.10 fail to validate the uniqueness and quantity of task actions within the UpdateRunTaskActions GraphQL operation, which allows an attacker to create task items containing an excessive number of actions triggered by specific posts, overloading the server and leading to a denial-of-service (DoS) condition.

Affected products

Mattermost: from 9.11.0 before 9.11.11; from 10.4.0 before 10.4.3; 10.5.0 — fixed in 10.4.3, 9.11.11

How to fix

Upgrade to a fixed version: Mattermost 10.4.3, 9.11.11. Check the vendor advisory for mitigations.

References

https://mattermost.com/security-updates

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