X509_CRL *X509_CRL_diff(X509_CRL *base, X509_CRL *newer,
                        EVP_PKEY *skey, const EVP_MD *md, unsigned int flags)
{
    X509_CRL *crl = NULL;
    int i;
    STACK_OF(X509_REVOKED) *revs = NULL;
    /* CRLs can't be delta already */
    if (base->base_crl_number || newer->base_crl_number) {
        X509err(X509_F_X509_CRL_DIFF, X509_R_CRL_ALREADY_DELTA);
        return NULL;
    }
    /* Base and new CRL must have a CRL number */
    if (!base->crl_number || !newer->crl_number) {
        X509err(X509_F_X509_CRL_DIFF, X509_R_NO_CRL_NUMBER);
        return NULL;
    }
    /* Issuer names must match */
    if (X509_NAME_cmp(X509_CRL_get_issuer(base), X509_CRL_get_issuer(newer))) {
        X509err(X509_F_X509_CRL_DIFF, X509_R_ISSUER_MISMATCH);
        return NULL;
    }
    /* AKID and IDP must match */
    if (!crl_extension_match(base, newer, NID_authority_key_identifier)) {
        X509err(X509_F_X509_CRL_DIFF, X509_R_AKID_MISMATCH);
        return NULL;
    }
    if (!crl_extension_match(base, newer, NID_issuing_distribution_point)) {
        X509err(X509_F_X509_CRL_DIFF, X509_R_IDP_MISMATCH);
        return NULL;
    }
    /* Newer CRL number must exceed full CRL number */
    if (ASN1_INTEGER_cmp(newer->crl_number, base->crl_number) <= 0) {
        X509err(X509_F_X509_CRL_DIFF, X509_R_NEWER_CRL_NOT_NEWER);
        return NULL;
    }
    /* CRLs must verify */
    if (skey && (X509_CRL_verify(base, skey) <= 0 ||
                 X509_CRL_verify(newer, skey) <= 0)) {
        X509err(X509_F_X509_CRL_DIFF, X509_R_CRL_VERIFY_FAILURE);
        return NULL;
    }
    /* Create new CRL */
    crl = X509_CRL_new();
    if (!crl || !X509_CRL_set_version(crl, 1))
        goto memerr;
    /* Set issuer name */
    if (!X509_CRL_set_issuer_name(crl, X509_CRL_get_issuer(newer)))
        goto memerr;

    if (!X509_CRL_set_lastUpdate(crl, X509_CRL_get_lastUpdate(newer)))
        goto memerr;
    if (!X509_CRL_set_nextUpdate(crl, X509_CRL_get_nextUpdate(newer)))
        goto memerr;

    /* Set base CRL number: must be critical */

    if (!X509_CRL_add1_ext_i2d(crl, NID_delta_crl, base->crl_number, 1, 0))
        goto memerr;

    /*
     * Copy extensions across from newest CRL to delta: this will set CRL
     * number to correct value too.
     */

    for (i = 0; i < X509_CRL_get_ext_count(newer); i++) {
        X509_EXTENSION *ext;
        ext = X509_CRL_get_ext(newer, i);
        if (!X509_CRL_add_ext(crl, ext, -1))
            goto memerr;
    }

    /* Go through revoked entries, copying as needed */

    revs = X509_CRL_get_REVOKED(newer);

    for (i = 0; i < sk_X509_REVOKED_num(revs); i++) {
        X509_REVOKED *rvn, *rvtmp;
        rvn = sk_X509_REVOKED_value(revs, i);
        /*
         * Add only if not also in base. TODO: need something cleverer here
         * for some more complex CRLs covering multiple CAs.
         */
        if (!X509_CRL_get0_by_serial(base, &rvtmp, rvn->serialNumber)) {
            rvtmp = X509_REVOKED_dup(rvn);
            if (!rvtmp)
                goto memerr;
            if (!X509_CRL_add0_revoked(crl, rvtmp)) {
                X509_REVOKED_free(rvtmp);
                goto memerr;
            }
        }
    }
    /* TODO: optionally prune deleted entries */

    if (skey && md && !X509_CRL_sign(crl, skey, md))
        goto memerr;

    return crl;

 memerr:
    X509err(X509_F_X509_CRL_DIFF, ERR_R_MALLOC_FAILURE);
    X509_CRL_free(crl);
    return NULL;
}

The product performs operations on a memory buffer, but it reads from or writes to a memory location outside the buffer's intended boundary. This may result in read or write operations on unexpected memory locations that could be linked to other variables, data structures, or internal program data.