CVE-2024-1402: Mattermost Server

Medium severity, CVSS 4.3. EPSS: 0.5% chance of exploitation in the next 30 days.

Mattermost fails to check if a custom emoji reaction exists when sending it to a post and to limit the amount of custom emojis allowed to be added in a post, allowing an attacker sending a huge amount of non-existent custom emojis in a post to crash the mobile app of a user seeing the post and to crash the server due to overloading when clients attempt to retrive the aforementioned post. 

Affected products

• Mattermost Mattermost Server: up to and including 8.1.7; from 9.0.0, up to and including 9.1.4; from 9.2.0, up to and including 9.2.3

Published 2024-02-09. Last modified 2026-06-17.