Medium severity · published May 27, 2026
CVE-2026-6957
Path traversal in Mattermost Legal Hold plugin via unsanitized file name from federated peer allows arbitrary file write.
4.9
CVSS
0.3%
EPSS
No
On KEV
Description
Mattermost Plugins versions <=1.1.5 fail to sanitize filenames received from federated peers before using them to construct export destination paths, which allows an administrator of a remote federated Mattermost server to write files to arbitrary locations within the target server's filestore via a malicious filename delivered through the shared-channel attachment sync protocol. Mattermost Advisory ID: MMSA-2026-00659
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:N/I:H/A:N
Attack vector
Network
Complexity
Low
Privileges
High
User interaction
None
Confidentiality
None
Integrity
High
Availability
None
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.3% · higher than 22% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
MA
Mattermost · Mattermost
through 1.1.5 · source: vendor
LH
Legal Hold · Mattermost
through 1.1.5 · source: NVD
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-6957
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-6957
Vendor Advisory
https://mattermost.com/security-updates
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