During a CMP root check‑key‑update, a typo in the certificate chain builder caused OpenSSL to add the new certificate itself instead of the old root CA certificate, rendering the chain verification ineffective. An attacker with valid registration authority credentials can therefore craft a CMP message containing a self‑signed certificate that the client will accept as a new trust anchor, achieving a trust‑anchor substitution. The vulnerability is a classic CWE‑295 misuse of certificate validation.

The issue affects the OpenSSL library in every release that implements the Certificate Management Protocol (CMP) root CaKeyUpdate functionality. No particular version is excluded in the available data, so all OpenSSL builds with CMP support are potentially vulnerable.

The CVSS score is 5.3, and the EPSS score is not available; the vulnerability is not listed in the CISA KEV catalog. Because the attack requires already‑in‑hand registration‑authority credentials, the likelihood of exploitation in the wild is limited, but the impact would be profound: the entire trust chain could be subverted for a compromised client. The potential attack vector would be an authenticated CMP session where the attacker sends a forged root‑CA‑update message over the network.