Mounir Idrassi

**Name of the Vulnerable Software and Affected Versions** OpenSSL (affected versions not specified) **Description** A malicious TLS server can trigger a memory leak in a TLS client that has enabled OCSP response checking. This occurs when the server sends an OCSP response containing no single response entries. During X.509 certificate chain verification, if the `X509 V FLAG OCSP RESP CHECK` or `X509 V FLAG OCSP RESP CHECK ALL` flags are enabled, the `OCSP BASICRESP` structure allocated by the `OCSP response get1 basic()` function is not freed due to an early return that bypasses cleanup code. An attacker can amplify the amount of leaked memory per handshake by padding the `certs` field of the `BasicOCSPResponse` with bogus certificates. For long-running clients that repeatedly connect to a malicious server, this can lead to memory exhaustion and a Denial of Service. This issue only affects client applications that explicitly enable OCSP response check verification flags, as this feature is not enabled by default. **Recommendations** At the moment, there is no information about a newer version that contains a fix for this vulnerability. As a temporary mitigation, avoid using the `X509 V FLAG OCSP RESP CHECK` and `X509 V FLAG OCSP RESP CHECK ALL` verification flags.