Mattermost versions 11.3.x <= 11.3.0, 11.2.x <= 11.2.2, 10.11.x <= 10.11.10 fail to properly validate User-Agent header tokens which allows an authenticated attacker to cause a request panic via a specially crafted User-Agent header. Mattermost Advisory ID: MMSA-2026-00586
{
"unresolved_ranges": [
{
"source": "AFFECTED_FIELD",
"extracted_events": [
{
"introduced": "11.3.0"
},
{
"last_affected": "11.3.0"
},
{
"introduced": "11.2.0"
},
{
"last_affected": "11.2.2"
},
{
"introduced": "10.11.0"
},
{
"last_affected": "10.11.10"
}
]
}
],
"osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/25xxx/CVE-2026-25783.json",
"cna_assigner": "Mattermost",
"cwe_ids": [
"CWE-1287"
]
}{
"source": "CPE_RANGE",
"cpe": "cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:*",
"extracted_events": [
{
"introduced": "10.11.0"
},
{
"fixed": "10.11.11"
},
{
"introduced": "11.2.0"
},
{
"fixed": "11.2.3"
},
{
"introduced": "11.3.0"
},
{
"fixed": "11.3.1"
}
]
}