int ssl3_send_client_certificate(SSL *s)
{
    X509 *x509 = NULL;
    EVP_PKEY *pkey = NULL;
    int i;

    if (s->state == SSL3_ST_CW_CERT_A) {
        /* Let cert callback update client certificates if required */
        if (s->cert->cert_cb) {
            i = s->cert->cert_cb(s, s->cert->cert_cb_arg);
            if (i < 0) {
                s->rwstate = SSL_X509_LOOKUP;
                return -1;
            }
            if (i == 0) {
                ssl3_send_alert(s, SSL3_AL_FATAL, SSL_AD_INTERNAL_ERROR);
                return 0;
            }
            s->rwstate = SSL_NOTHING;
        }
        if (ssl3_check_client_certificate(s))
            s->state = SSL3_ST_CW_CERT_C;
        else
            s->state = SSL3_ST_CW_CERT_B;
    }

    /* We need to get a client cert */
    if (s->state == SSL3_ST_CW_CERT_B) {
        /*
         * If we get an error, we need to ssl->rwstate=SSL_X509_LOOKUP;
         * return(-1); We then get retied later
         */
        i = 0;
        i = ssl_do_client_cert_cb(s, &x509, &pkey);
        if (i < 0) {
            s->rwstate = SSL_X509_LOOKUP;
            return (-1);
        }
        s->rwstate = SSL_NOTHING;
        if ((i == 1) && (pkey != NULL) && (x509 != NULL)) {
            s->state = SSL3_ST_CW_CERT_B;
            if (!SSL_use_certificate(s, x509) || !SSL_use_PrivateKey(s, pkey))
                i = 0;
        } else if (i == 1) {
            i = 0;
            SSLerr(SSL_F_SSL3_SEND_CLIENT_CERTIFICATE,
                   SSL_R_BAD_DATA_RETURNED_BY_CALLBACK);
        }

        if (x509 != NULL)
            X509_free(x509);
        if (pkey != NULL)
            EVP_PKEY_free(pkey);
        if (i && !ssl3_check_client_certificate(s))
            i = 0;
        if (i == 0) {
            if (s->version == SSL3_VERSION) {
                s->s3->tmp.cert_req = 0;
                ssl3_send_alert(s, SSL3_AL_WARNING, SSL_AD_NO_CERTIFICATE);
                return (1);
            } else {
                s->s3->tmp.cert_req = 2;
            }
        }

        /* Ok, we have a cert */
        s->state = SSL3_ST_CW_CERT_C;
    }

    if (s->state == SSL3_ST_CW_CERT_C) {
        s->state = SSL3_ST_CW_CERT_D;
        if (!ssl3_output_cert_chain(s,
                                    (s->s3->tmp.cert_req ==
                                     2) ? NULL : s->cert->key)) {
            SSLerr(SSL_F_SSL3_SEND_CLIENT_CERTIFICATE, ERR_R_INTERNAL_ERROR);
            ssl3_send_alert(s, SSL3_AL_FATAL, SSL_AD_INTERNAL_ERROR);
            return 0;
        }
    }
    /* SSL3_ST_CW_CERT_D */
    return ssl_do_write(s);
}

This weakness pertains to the use of cryptographic functions that are weak, misconfigured, or outdated, which undermines the intended protection of encrypted data and communications.