Medium severity · published Jul 13, 2026
CVE-2026-10103
Authenticated remote cluster can modify or delete posts it does not own in Mattermost Connected Workspaces shared channels
4.3
CVSS
0.2%
EPSS
No
On KEV
Description
Mattermost versions 11.7.x <= 11.7.2, 11.6.x <= 11.6.4, 10.11.x <= 10.11.19 fail to verify post ownership in the shared channel inbound sync handler, which allows an authenticated remote cluster to modify or delete posts authored by local users or other remotes via crafted sync messages referencing arbitrary post IDs in channels shared with that remote.. Mattermost Advisory ID: MMSA-2026-00689
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N
Attack vector
Network
Complexity
Low
Privileges
Low
User interaction
None
Confidentiality
None
Integrity
Low
Availability
None
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.2% · higher than 15% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
MA
Mattermost · Mattermost
11.7.0 through 11.7.2; 11.6.0 through 11.6.4; 10.11.0 through 10.11.19 · source: vendor
MS
Mattermost Server · Mattermost
10.11.0 before 10.11.20; 11.6.0 before 11.6.5; 11.7.0 before 11.7.3 · source: NVD
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-10103
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-10103
Vendor Advisory
https://mattermost.com/security-updates
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