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
{
"unresolved_ranges": [
{
"extracted_events": [
{
"introduced": "11.7.0"
},
{
"last_affected": "11.7.0"
},
{
"introduced": "11.6.0"
},
{
"last_affected": "11.6.2"
},
{
"introduced": "11.5.0"
},
{
"last_affected": "11.5.5"
},
{
"introduced": "10.11.0"
},
{
"last_affected": "10.11.17"
}
],
"source": "AFFECTED_FIELD"
}
],
"osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/6xxx/CVE-2026-6673.json",
"cna_assigner": "Mattermost",
"cwe_ids": [
"CWE-306"
]
}{
"extracted_events": [
{
"introduced": "10.11.0"
},
{
"fixed": "10.11.18"
},
{
"introduced": "11.5.0"
},
{
"fixed": "11.5.6"
},
{
"introduced": "11.6.0"
},
{
"fixed": "11.6.3"
},
{
"introduced": "11.7.0"
},
{
"fixed": "11.7.1"
}
],
"cpe": "cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:*",
"source": "CPE_RANGE"
}