What’s Vulnerable › Vulnerabilities

CVE-2024-29977: Malicious remote can create arbitrary reactions on arbitrary posts

• Severity: medium (CVSS 4.3 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.3% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2024-08-01 · updated 2026-06-17
• Weakness: CWE-284

Description

Mattermost versions 9.9.x <= 9.9.0, 9.5.x <= 9.5.6 fail to properly validate synced reactions, when shared channels are enabled, which allows a malicious remote to create arbitrary reactions on arbitrary posts

Affected products

• Mattermost App Framework: from 9.5.0 before 9.5.7; 9.9.0 — fixed in 9.5.7

How to fix

Upgrade to a fixed version: Mattermost App Framework 9.5.7. Check the vendor advisory for mitigations.

References

• https://mattermost.com/security-updates

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