Mattermost versions 11.6.x <= 11.6.0, 11.5.x <= 11.5.3, 11.4.x <= 11.4.4, 10.11.x <= 10.11.14 fail to filter nil elements from outgoing webhook attachment payloads before processing, which allows an authenticated user to cause a denial of service (server process termination) via a crafted webhook callback response containing a null attachment entry.. Mattermost Advisory ID: MMSA-2026-00641
{
"cna_assigner": "Mattermost",
"cwe_ids": [
"CWE-754"
],
"unresolved_ranges": [
{
"source": "AFFECTED_FIELD",
"extracted_events": [
{
"introduced": "11.6.0"
},
{
"last_affected": "11.6.0"
},
{
"introduced": "11.5.0"
},
{
"last_affected": "11.5.3"
},
{
"introduced": "11.4.0"
},
{
"last_affected": "11.4.4"
},
{
"introduced": "10.11.0"
},
{
"last_affected": "10.11.14"
}
]
}
],
"osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/4xxx/CVE-2026-4915.json"
}{
"source": "CPE_RANGE",
"cpe": "cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:*",
"extracted_events": [
{
"introduced": "10.11.0"
},
{
"fixed": "10.11.15"
},
{
"introduced": "11.4.0"
},
{
"fixed": "11.4.5"
},
{
"introduced": "11.5.0"
},
{
"fixed": "11.5.4"
},
{
"introduced": "11.6.0"
},
{
"fixed": "11.6.1"
}
]
}