CVE-2026-75588 PUBLISHED

Mattermost Desktop App plugin popout scheme validation bypass

Assigner: Mattermost
Reserved: 17.08.2026 Published: 17.09.2026 Updated: 17.09.2026

Mattermost Desktop App versions <=6.2 6.2.2.0 fail to validate the URL scheme when checking whether a target URL is internal to the connected server, which allows a network-positioned attacker to load a plugin popout window over an insecure connection via a link using a downgraded URL scheme. Mattermost Advisory ID: MMSA-2026-00717

Metrics

CVSS 3.1

CVSS Vector: CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:U/C:N/I:L/A:N
CVSS Score: 2.6

Attack Vector	Network	Scope	Unchanged
Attack Complexity	High	Confidentiality Impact	None
Privileges Required	Low	Integrity Impact	Low
User Interaction	Required	Availability Impact	None

CVSS 3.1

Product Status

Vendor	Mattermost
Product	Mattermost
Versions	Default: unaffected affected from 0 to 6.2.2 (incl.) Version 6.3.0 is unaffected Version 6.2.3.0 is unaffected

Solutions

Update Mattermost Desktop App to versions 6.3.0, 6.2.3.0 or higher.

Credits

Juho Forsén finder

References

MMSA-2026-00717

Problem Types

CWE-1287: Improper Validation of Specified Type of Input CWE