CVE-2025-20621

Webapp crash via object that can't be cast to String in Attachment Field

Description

Mattermost versions 10.2.x <= 10.2.0, 9.11.x <= 9.11.5, 10.0.x <= 10.0.3, 10.1.x <= 10.1.3 fail to properly handle posts with attachments containing fields that cannot be cast to a String, which allows an attacker to cause the webapp to crash via creating and sending such a post to a channel.

Remediation

Solution:

  • Update Mattermost to versions 10.3.0, 2.23.0, 10.2.1, 9.11.6, 10.0.4, 10.1.4 or higher.

Category

6.5
CVSS
Severity: Medium
CVSS 3.1 •
EPSS 0.14%
Affected: Mattermost Mattermost
Published at:
Updated at:

References

Link Tags
https://mattermost.com/security-updates

Frequently Asked Questions

What is the severity of CVE-2025-20621?
CVE-2025-20621 has been scored as a medium severity vulnerability.
How to fix CVE-2025-20621?
To fix CVE-2025-20621: Update Mattermost to versions 10.3.0, 2.23.0, 10.2.1, 9.11.6, 10.0.4, 10.1.4 or higher.
Is CVE-2025-20621 being actively exploited in the wild?
As for now, there are no information to confirm that CVE-2025-20621 is being actively exploited. According to its EPSS score, there is a ~0% probability that this vulnerability will be exploited by malicious actors in the next 30 days.
What software or system is affected by CVE-2025-20621?
CVE-2025-20621 affects Mattermost Mattermost.
This platform uses data from the NIST NVD, MITRE CVE, MITRE CWE, First.org and CISA KEV but is not endorsed or certified by these entities. CVE is a registred trademark of the MITRE Corporation and the authoritative source of CVE content is MITRE's CVE web site. CWE is a registred trademark of the MITRE Corporation and the authoritative source of CWE content is MITRE's CWE web site.
© 2025 Under My Watch. All Rights Reserved.