How severe is CVE-2026-3109?

CVE-2026-3109 has a CVSS 3.x base score of 2.2, rated low severity. It is exploitable over network with high attack complexity, requires high privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability low.

Is CVE-2026-3109 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-2026-3109?

CVE-2026-3109 affects Mattermost Mattermost Server. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2026-3109?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

Does CVE-2026-3109 have an EU (EUVD) identifier?

Yes. CVE-2026-3109 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-16236.

When was CVE-2026-3109 published?

CVE-2026-3109 was published on 2026-03-26 and last updated on 2026-06-17.

CVE-2026-3109

CVE-2026-3109 is a low-severity vulnerability in Mattermost Mattermost Server with a CVSS 3.x base score of 2.2. 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-754.

Key facts

Severity: Low (CVSS 3.x base score 2.2)
EPSS exploit prediction: 0% (21st percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-16236
Weakness: CWE-754
Affected product: Mattermost Mattermost Server
Published: 2026-03-26
Last modified: 2026-06-17

Description

Mattermost Plugins versions <=11.4 10.11.11.0 fail to validate webhook request timestamps which allows an attacker to corrupt Zoom meeting state in Mattermost via replayed webhook requests. Mattermost Advisory ID: MMSA-2026-00584

Frequently asked questions

What is CVE-2026-3109?: Mattermost Plugins versions <=11.4 10.11.11.0 fail to validate webhook request timestamps which allows an attacker to corrupt Zoom meeting state in Mattermost via replayed webhook requests. Mattermost Advisory ID: MMSA-2026-00584
How severe is CVE-2026-3109?: CVE-2026-3109 has a CVSS 3.x base score of 2.2, rated low severity. It is exploitable over network with high attack complexity, requires high privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability low.
Is CVE-2026-3109 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-2026-3109?: CVE-2026-3109 affects Mattermost Mattermost Server. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2026-3109?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
Does CVE-2026-3109 have an EU (EUVD) identifier?: Yes. CVE-2026-3109 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-16236.
When was CVE-2026-3109 published?: CVE-2026-3109 was published on 2026-03-26 and last updated on 2026-06-17.

References

https://mattermost.com/security-updates

Affected products (1)

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

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