CVE-2026-27769: Connected Workspaces: Malicious remote server can manipulate arbitrary user's status

Severity: low (CVSS 2.7 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.2% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-04-15 · updated 2026-06-17
Weakness: CWE-862

Description

Mattermost versions 10.11.x <= 10.11.12 fail to validate whether users were correctly owned by the correct Connected Workspace which allows a malicious remote server connected using the Conntexted Workspaces feature to change the displayed status of local users via the Connected Workspaces API.. Mattermost Advisory ID: MMSA-2026-00603

Affected products

Mattermost: from 10.11.0 before 10.11.13 — fixed in 10.11.13

How to fix

Upgrade to a fixed version: Mattermost 10.11.13. Check the vendor advisory for mitigations.

References

https://mattermost.com/security-updates

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