From 8ce6f8d166acf02d6833b9f37fb5cd2ca903a4a5 Mon Sep 17 00:00:00 2001 From: Arne Schwabe Date: Sat, 4 Apr 2026 09:23:30 +0200 Subject: [PATCH] Use ASN1_BIT_STRING_get_bit to check for netscape certificate usage The ASN_BIT_STRING object has become opaque in OpenSSL 4.0. So instead of accessing the internal, we have to use a method now to check these attributes. The bit counting in ASN.1 and of this method is a bit strange and it will count bits from the left instead of the right, so the previous mask of 0x80 for clients is now 0 and 0x40 for server is now 1. Change-Id: I77500d435f212a4bf42ee8cfca07d0285fe694f2 Signed-off-by: Arne Schwabe Acked-by: Frank Lichtenheld Gerrit URL: https://gerrit.openvpn.net/c/openvpn/+/1587 Message-Id: <20260404072336.30014-1-gert@greenie.muc.de> URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg36446.html Signed-off-by: Gert Doering --- src/openvpn/ssl_verify_openssl.c | 36 ++++++++++++++++++++------------ 1 file changed, 23 insertions(+), 13 deletions(-) diff --git a/src/openvpn/ssl_verify_openssl.c b/src/openvpn/ssl_verify_openssl.c index 08946cdc..c70022f1 100644 --- a/src/openvpn/ssl_verify_openssl.c +++ b/src/openvpn/ssl_verify_openssl.c @@ -609,22 +609,27 @@ x509_verify_ns_cert_type(openvpn_x509_cert_t *peer_cert, const int usage) if (usage == NS_CERT_CHECK_CLIENT) { /* - * Unfortunately, X509_check_purpose() does some weird thing that + * Unfortunately, X509_check_purpose() before OpenSSL 4.0 does some weird thing that * prevent it to take a const argument */ result_t result = X509_check_purpose(peer_cert, X509_PURPOSE_SSL_CLIENT, 0) ? SUCCESS : FAILURE; - /* - * old versions of OpenSSL allow us to make the less strict check we used to - * do. If this less strict check pass, warn user that this might not be the - * case when its distribution will update to OpenSSL 1.1 + * Note that we did not check for netscape certificate type here but + * instead a general SSL/TLS client purpose. These nscert attributes + * might stop being accepted by TLS libraries in the future. + * Currently, OpenSSL 4.0 and aws-lc 1.9.0 still consider nscert client + * as acceptable. + * + * So in case that this check failed, we now check if this is caused + * by the check above no longer recognising nscert attributes. */ if (result == FAILURE) { ASN1_BIT_STRING *ns; ns = X509_get_ext_d2i(peer_cert, NID_netscape_cert_type, NULL, NULL); - result = (ns && ASN1_STRING_length(ns) > 0 && (ASN1_STRING_get0_data(ns)[0] & NS_SSL_CLIENT)) ? SUCCESS : FAILURE; + // bit 0 is to check if certificate is the client certificate + result = ASN1_BIT_STRING_get_bit(ns, 0) ? SUCCESS : FAILURE; if (result == SUCCESS) { msg(M_WARN, "X509: Certificate is a client certificate yet it's purpose " @@ -637,22 +642,27 @@ x509_verify_ns_cert_type(openvpn_x509_cert_t *peer_cert, const int usage) if (usage == NS_CERT_CHECK_SERVER) { /* - * Unfortunately, X509_check_purpose() does some weird thing that + * Unfortunately, X509_check_purpose() before OpenSSL 4.0 does some weird thing that * prevent it to take a const argument */ result_t result = X509_check_purpose(peer_cert, X509_PURPOSE_SSL_SERVER, 0) ? SUCCESS : FAILURE; /* - * old versions of OpenSSL allow us to make the less strict check we used to - * do. If this less strict check pass, warn user that this might not be the - * case when its distribution will update to OpenSSL 1.1 + * Note that we did not check for netscape certificate type here but + * instead a general SSL/TLS server purpose. These nscert attributes + * might stop being accepted by TLS libraries in the future. + * Currently, OpenSSL 4.0 and aws-lc 1.9.0 still consider nscert server + * as acceptable. + * + * So in case that this check failed, we now check if this is caused + * by the check above no longer recognising nscert attributes. */ if (result == FAILURE) { - ASN1_BIT_STRING *ns; - ns = X509_get_ext_d2i(peer_cert, NID_netscape_cert_type, NULL, NULL); - result = (ns && ASN1_STRING_length(ns) > 0 && (ASN1_STRING_get0_data(ns)[0] & NS_SSL_SERVER)) ? SUCCESS : FAILURE; + ASN1_BIT_STRING *ns = X509_get_ext_d2i(peer_cert, NID_netscape_cert_type, NULL, NULL); + // Server bit is 1 for ASN1_BIT_STRING_get_bit + result = ASN1_BIT_STRING_get_bit(ns, 1) ? SUCCESS : FAILURE; if (result == SUCCESS) { msg(M_WARN, "X509: Certificate is a server certificate yet it's purpose "