Fleet before 4.86.2 contains a denial of service vulnerability that allows unauthenticated attackers to exhaust server memory through quadratic XML canonicalization of unsigned SAML responses. Attackers can send a single crafted SAML response with deeply nested elements declaring new namespace prefixes to POST /api/v1/fleet/sso/callback, crashing the Fleet server.
{
"cna_assigner": "VulnCheck",
"cwe_ids": [
"CWE-407"
],
"osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/126xxx/CVE-2026-126401.json"
}{
"extracted_events": [
{
"range": [
{
"introduced": "0"
},
{
"fixed": "4.86.2"
}
],
"source": "AFFECTED_FIELD",
"strategy": "StandardRange"
}
]
}