Is CVE-2026-3109 in the CISA KEV catalog?

No. CVE-2026-3109 is not currently on the CISA Known Exploited Vulnerabilities list.

What is the CVSS severity of CVE-2026-3109?

CVE-2026-3109 has a CVSS v3 base score of 2.2 (LOW).

What is the EPSS score for CVE-2026-3109?

CVE-2026-3109 has an EPSS score of 0.29% (21th percentile), estimating the probability of exploitation in the next 30 days.

How do I fix CVE-2026-3109?

Upgrade mattermost server to 10.11.12 or later.

CVE & CISA-KEV Catalog

CVE-2026-3109

LOW

2.2

CVSS v3

NVD

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

CWE-754

How to fix

Remediation Available

mattermost serverNVD

Affected:>= 10.11.0, < 10.11.12Fixed in:10.11.12CVE-2026-3109derived from NVD

Remediation is compiled from vendor and distribution security advisories. Always confirm against the linked source for your exact version and platform.

CVSS v3 Vector

Exploitability

Attack VectorNetwork

Attack ComplexityHigh

Privileges RequiredHigh

User InteractionNone

ScopeUnchanged

Impact

ConfidentialityNone

IntegrityNone

AvailabilityLow

CVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:L

Exploit Intelligence

0.29%probability of exploitation in 30 days

21stpercentile

Low risk: more likely to be exploited than 21% of all known CVEs.

References

Vendor Advisory1

mattermost.com

Related Vulnerabilities

Other CWE-754 vulnerabilities, ordered by exploit likelihood. View all

CVE	Severity	CVSS	EPSS	Exploited	Fix
CVE-2024-4367	High	8.8	73%	-	Fix
CVE-2022-39288	High	7.5	59%	-	Fix
CVE-2023-30591	High	7.5	54%	-	-
CVE-2023-41993	High	8.8	29%	KEV	Fix
CVE-2024-43044	High	8.8	29%	-	Fix
CVE-2024-3393	High	7.5	27%	KEV	Fix

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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2026-06-08.