Is CVE-2026-6673 in the CISA KEV catalog?

No. CVE-2026-6673 is not currently on the CISA Known Exploited Vulnerabilities list.

What is the CVSS severity of CVE-2026-6673?

CVE-2026-6673 has a CVSS v3 base score of 6.4 (MEDIUM).

What is the EPSS score for CVE-2026-6673?

CVE-2026-6673 has an EPSS score of 0.18% (7th percentile), estimating the probability of exploitation in the next 30 days.

How do I fix CVE-2026-6673?

Upgrade mattermost server to 11.7.1 or later.

CVE & CISA-KEV Catalog

CVE-2026-6673

MEDIUM

6.4

CVSS v3

NVD

Description

Mattermost versions 11.7.x <= 11.7.0, 11.6.x <= 11.6.2, 11.5.x <= 11.5.5, 10.11.x <= 10.11.17 fail to authenticate Atlassian Connect installed callbacks, allowing a remote unauthenticated attacker to inject a rogue sharedSecret and disrupt the Jira integration via POST to /ac/installed during the pending-install window.. Mattermost Advisory ID: MMSA-2026-00654

CWE-306Missing Authentication for Critical Function

How to fix

Remediation Available

mattermost serverNVD

Affected:>= 11.7.0, < 11.7.1Fixed in:11.7.1CVE-2026-6673derived 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 RequiredLow

User InteractionRequired

ScopeUnchanged

Impact

ConfidentialityNone

IntegrityHigh

AvailabilityHigh

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

Exploit Intelligence

0.18%probability of exploitation in 30 days

7thpercentile

Low risk: more likely to be exploited than 7% of all known CVEs.

References

Vendor Advisory1

mattermost.com

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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 2026-06-23.