A flaw was found in Keycloak. The cross-session verification proof is keyed only by (local userId, idpAlias) and is not bound to the upstream identity that was actually verified, so a second upstream account on the same IdP can consume it and get linked to the victim's local account.
{
"github_reviewed": true,
"github_reviewed_at": "2026-06-11T16:40:55Z",
"nvd_published_at": "2026-05-20T17:16:32Z",
"severity": "MODERATE",
"cwe_ids": [
"CWE-639"
]
}