How severe is CVE-2026-6961?

CVE-2026-6961 has a CVSS 3.x base score of 7.6, rated high severity. It is exploitable over network with low attack complexity, requires high privileges and no user interaction. Impact on confidentiality is none, integrity high, and availability low.

Is CVE-2026-6961 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (21st percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-6961?

CVE-2026-6961 affects Mattermost Mattermost Server. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2026-6961?

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-2026-6961 have an EU (EUVD) identifier?

Yes. CVE-2026-6961 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-36504.

When was CVE-2026-6961 published?

CVE-2026-6961 was published on 2026-06-12 and last updated on 2026-06-18.

CVE-2026-6961

CVE-2026-6961 is a high-severity vulnerability in Mattermost Mattermost Server with a CVSS 3.x base score of 7.6. 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 7.6)
EPSS exploit prediction: 0% (21st percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-36504
Weakness: CWE-22
Affected product: Mattermost Mattermost Server
Published: 2026-06-12
Last modified: 2026-06-18

Description

Mattermost versions 11.6.x <= 11.6.1, 11.5.x <= 11.5.4, 10.11.x <= 10.11.15, 10.11.x <= 10.11.16 Mattermost fails to sanitize FileInfo.Name received from federated peers during shared channel file sync, which allows an attacker who controls a federated server to write files to arbitrary locations within the target server's filestore via path traversal sequences in the filename field.. Mattermost Advisory ID: MMSA-2026-00661

Frequently asked questions

What is CVE-2026-6961?: Mattermost versions 11.6.x <= 11.6.1, 11.5.x <= 11.5.4, 10.11.x <= 10.11.15, 10.11.x <= 10.11.16 Mattermost fails to sanitize FileInfo.Name received from federated peers during shared channel file sync, which allows an attacker who controls a federated server to write files to arbitrary locations within the target server's filestore via path traversal sequences in the filename field.. Mattermost Advisory ID: MMSA-2026-00661
How severe is CVE-2026-6961?: CVE-2026-6961 has a CVSS 3.x base score of 7.6, rated high severity. It is exploitable over network with low attack complexity, requires high privileges and no user interaction. Impact on confidentiality is none, integrity high, and availability low.
Is CVE-2026-6961 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (21st percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-6961?: CVE-2026-6961 affects Mattermost Mattermost Server. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2026-6961?: 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-2026-6961 have an EU (EUVD) identifier?: Yes. CVE-2026-6961 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-36504.
When was CVE-2026-6961 published?: CVE-2026-6961 was published on 2026-06-12 and last updated on 2026-06-18.

References

https://mattermost.com/security-updates

Affected products (1)

cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:*

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