CVE-2026-6957
CVE-2026-6957 is a high-severity vulnerability in Mattermost Legal Hold with a CVSS 3.x base score of 8.0. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-22.
Key facts
- Severity: High (CVSS 3.x base score 8.0)
- EPSS exploit prediction: 0% (22nd percentile)
- Actively exploited: Not listed in CISA KEV
- EU (EUVD) id: EUVD-2026-32523
- Weakness: CWE-22
- Affected product: Mattermost Legal Hold
- Published:
- Last modified:
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
Frequently asked questions
- What is CVE-2026-6957?
- 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
- How severe is CVE-2026-6957?
- CVE-2026-6957 has a CVSS 3.x base score of 8.0, rated high severity. It is exploitable over network with high attack complexity, requires high privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.
- Is CVE-2026-6957 being actively exploited?
- It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (22nd percentile), an estimate of the probability of exploitation in the next 30 days.
- What products are affected by CVE-2026-6957?
- CVE-2026-6957 affects Mattermost Legal Hold. See the affected-products list for the exact vulnerable versions.
- How do I fix CVE-2026-6957?
- Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
- Does CVE-2026-6957 have an EU (EUVD) identifier?
- Yes. CVE-2026-6957 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-32523.
- When was CVE-2026-6957 published?
- CVE-2026-6957 was published on 2026-05-27 and last updated on 2026-06-17.
References
Affected products (1)
- cpe:2.3:a:mattermost:legal_hold:*:*:*:*:*:mattermost:*:*
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