static int check_chain_extensions(X509_STORE_CTX *ctx)
{
    int i, ok = 0, must_be_ca, plen = 0;
    X509 *x;
    int (*cb) (int xok, X509_STORE_CTX *xctx);
    int proxy_path_length = 0;
    int purpose;
    int allow_proxy_certs;
    cb = ctx->verify_cb;

    /*-
     *  must_be_ca can have 1 of 3 values:
     * -1: we accept both CA and non-CA certificates, to allow direct
     *     use of self-signed certificates (which are marked as CA).
     * 0:  we only accept non-CA certificates.  This is currently not
     *     used, but the possibility is present for future extensions.
     * 1:  we only accept CA certificates.  This is currently used for
     *     all certificates in the chain except the leaf certificate.
     */
    must_be_ca = -1;

    /* CRL path validation */
    if (ctx->parent) {
        allow_proxy_certs = 0;
        purpose = X509_PURPOSE_CRL_SIGN;
    } else {
        allow_proxy_certs =
            ! !(ctx->param->flags & X509_V_FLAG_ALLOW_PROXY_CERTS);
        /*
         * A hack to keep people who don't want to modify their software
         * happy
         */
        if (getenv("OPENSSL_ALLOW_PROXY_CERTS"))
            allow_proxy_certs = 1;
        purpose = ctx->param->purpose;
    }

    /* Check all untrusted certificates */
    for (i = 0; i < ctx->last_untrusted; i++) {
        int ret;
        x = sk_X509_value(ctx->chain, i);
        if (!(ctx->param->flags & X509_V_FLAG_IGNORE_CRITICAL)
            && (x->ex_flags & EXFLAG_CRITICAL)) {
            ctx->error = X509_V_ERR_UNHANDLED_CRITICAL_EXTENSION;
            ctx->error_depth = i;
            ctx->current_cert = x;
            ok = cb(0, ctx);
            if (!ok)
                goto end;
        }
        if (!allow_proxy_certs && (x->ex_flags & EXFLAG_PROXY)) {
            ctx->error = X509_V_ERR_PROXY_CERTIFICATES_NOT_ALLOWED;
            ctx->error_depth = i;
            ctx->current_cert = x;
            ok = cb(0, ctx);
            if (!ok)
                goto end;
        }
        ret = X509_check_ca(x);
        switch (must_be_ca) {
        case -1:
            if ((ctx->param->flags & X509_V_FLAG_X509_STRICT)
                && (ret != 1) && (ret != 0)) {
                ret = 0;
                ctx->error = X509_V_ERR_INVALID_CA;
            } else
                ret = 1;
            break;
        case 0:
            if (ret != 0) {
                ret = 0;
                ctx->error = X509_V_ERR_INVALID_NON_CA;
            } else
                ret = 1;
            break;
        default:
            if ((ret == 0)
                || ((ctx->param->flags & X509_V_FLAG_X509_STRICT)
                    && (ret != 1))) {
                ret = 0;
                ctx->error = X509_V_ERR_INVALID_CA;
            } else
                ret = 1;
            break;
        }
        if (ret == 0) {
            ctx->error_depth = i;
            ctx->current_cert = x;
            ok = cb(0, ctx);
            if (!ok)
                goto end;
        }
        if (ctx->param->purpose > 0) {
            ret = X509_check_purpose(x, purpose, must_be_ca > 0);
            if ((ret == 0)
                || ((ctx->param->flags & X509_V_FLAG_X509_STRICT)
                    && (ret != 1))) {
                ctx->error = X509_V_ERR_INVALID_PURPOSE;
                ctx->error_depth = i;
                ctx->current_cert = x;
                ok = cb(0, ctx);
                if (!ok)
                    goto end;
            }
        }
        /* Check pathlen if not self issued */
        if ((i > 1) && !(x->ex_flags & EXFLAG_SI)
            && (x->ex_pathlen != -1)
            && (plen > (x->ex_pathlen + proxy_path_length + 1))) {
            ctx->error = X509_V_ERR_PATH_LENGTH_EXCEEDED;
            ctx->error_depth = i;
            ctx->current_cert = x;
            ok = cb(0, ctx);
            if (!ok)
                goto end;
        }
        /* Increment path length if not self issued */
        if (!(x->ex_flags & EXFLAG_SI))
            plen++;
        /*
         * If this certificate is a proxy certificate, the next certificate
         * must be another proxy certificate or a EE certificate.  If not,
         * the next certificate must be a CA certificate.
         */
        if (x->ex_flags & EXFLAG_PROXY) {
            if (x->ex_pcpathlen != -1 && i > x->ex_pcpathlen) {
                ctx->error = X509_V_ERR_PROXY_PATH_LENGTH_EXCEEDED;
                ctx->error_depth = i;
                ctx->current_cert = x;
                ok = cb(0, ctx);
                if (!ok)
                    goto end;
            }
            proxy_path_length++;
            must_be_ca = 0;
        } else
            must_be_ca = 1;
    }
    ok = 1;
 end:
    return ok;
}

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.