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. Fetching posts with huge amounts of reactions results in Uncontrolled Resource Consumption.

References

• https://nvd.nist.gov/vuln/detail/CVE-2024-1402
• https://mattermost.com/security-updates
• mattermost/mattermost@64cb0ca
• mattermost/mattermost@6d2440d
• mattermost/mattermost@81190e2