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CVE-2026-6673

Mattermost Jira plugin had unauthenticated {{/ac/installed}} lifecycle callback during pending Jira Cloud install

Published: Jun 22, 2026Updated: Jun 22, 2026 Sources: CVE List NVDCWE-306
NVD MITRE
6.4CVSSMEDIUM
EPSS Score
N/A
CISA KEV
Not in KEV
Exploits
No Known Exploits
Remediation
Patch Available

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

CVSS Vector Breakdown

AV:NAC:HPR:LUI:RS:UC:NI:HA:H
Exploitability
AV:NAttack Vector
Network
AC:HAttack Complexity
High
PR:LPrivileges Required
Low
UI:RUser Interaction
Required
Scope
S:UScope
Unchanged
Impact
C:NConfidentiality
None
I:HIntegrity
High
A:HAvailability
High
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Weaknesses

CWE-306

Affected Products

MattermostMattermost
On-premWeb App
Communications / messaging-chat
mattermostcommercialUSCommunications

Attack Graph

Products CVE Techniques Tactics

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Exploitability

Official Patch Available

MITRE ATT&CK

2 techniques
Initial Access
View detailed technique mapping

References

https://mattermost.com/security-updates
mattermost.com

Timeline

Published
Jun 22, 2026
Last Updated
Jun 22, 2026

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