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.

CVSS vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Attack vector

Network

Complexity

Low

Privileges

None

User interaction

None

Confidentiality

None

Integrity

None

Availability

High

Scope

Unchanged

Exploitation

Is it being used?

Exploit prediction (EPSS)0.5% · higher than 41% of CVEs

Exploited in the wildNo evidence yet

CISA KEVNot listed

Ransomware campaign useNot known

Affected products

Which versions

MA

Mattermost · Mattermost

10.2.0 through 10.2.0; 9.11.0 through 9.11.5; 10.0.0 through 10.0.3; 10.1.0 through 10.1.3 · source: vendor

MS

Mattermost Server · Mattermost

9.11.0 before 9.11.6; 10.0.0 before 10.0.4; 10.1.0 before 10.1.4; 10.2.0 · source: NVD