static int get_crl_sk(X509_STORE_CTX *ctx, X509_CRL **pcrl, X509_CRL **pdcrl,
                      X509 **pissuer, int *pscore, unsigned int *preasons,
                      STACK_OF(X509_CRL) *crls)
{
    int i, crl_score, best_score = *pscore;
    unsigned int reasons, best_reasons = 0;
    X509 *x = ctx->current_cert;
    X509_CRL *crl, *best_crl = NULL;
    X509 *crl_issuer = NULL, *best_crl_issuer = NULL;

    for (i = 0; i < sk_X509_CRL_num(crls); i++) {
         crl = sk_X509_CRL_value(crls, i);
         reasons = *preasons;
         crl_score = get_crl_score(ctx, &crl_issuer, &reasons, crl, x);
        if (crl_score < best_score || crl_score == 0)
             continue;
         /* If current CRL is equivalent use it if it is newer */
        if (crl_score == best_score && best_crl != NULL) {
             int day, sec;
             if (ASN1_TIME_diff(&day, &sec, X509_CRL_get_lastUpdate(best_crl),
                                X509_CRL_get_lastUpdate(crl)) == 0)
                continue;
            /*
             * ASN1_TIME_diff never returns inconsistent signs for |day|
             * and |sec|.
             */
            if (day <= 0 && sec <= 0)
                continue;
        }
        best_crl = crl;
        best_crl_issuer = crl_issuer;
        best_score = crl_score;
        best_reasons = reasons;
    }

    if (best_crl) {
        if (*pcrl)
            X509_CRL_free(*pcrl);
        *pcrl = best_crl;
        *pissuer = best_crl_issuer;
        *pscore = best_score;
        *preasons = best_reasons;
        CRYPTO_add(&best_crl->references, 1, CRYPTO_LOCK_X509_CRL);
        if (*pdcrl) {
            X509_CRL_free(*pdcrl);
            *pdcrl = NULL;
        }
        get_delta_sk(ctx, pdcrl, pscore, best_crl, crls);
    }

    if (best_score >= CRL_SCORE_VALID)
        return 1;

    return 0;
}

The product dereferences a pointer that it expects to be valid but is NULL.