From a6dbec1cb481d6f0237372a7dec059f1c572b7b7 Mon Sep 17 00:00:00 2001 From: Steffan Karger Date: Mon, 19 Jun 2017 11:28:39 +0200 Subject: [PATCH] Restrict --x509-alt-username extension types The code never supported all extension types. Make this explicit by only allowing subjectAltName and issuerAltName (for which the current code does work). Using unsupported extension fields would most likely cause OpenVPN to crash as soon as a client connects. This does not have a real-world security impact, as such a configuration would not be possible to use in practice. This bug was discovered, analysed and reported to the OpenVPN team by Guido Vranken. Note: small code changes in to avoid "variable declaration in the middle of a code block" when backporting changes to extract_x509_extension(), as 2.3 can not assume a C99 compiler. Signed-off-by: Steffan Karger Acked-by: Gert Doering Acked-by: David Sommerseth Acked-by: Guido Vranken Message-Id: <1497864520-12219-5-git-send-email-steffan.karger@fox-it.com> URL: https://www.mail-archive.com/search?l=mid&q=1497864520-12219-5-git-send-email-steffan.karger@fox-it.com Signed-off-by: Gert Doering (cherry picked from commit d2a19185fd78030ce4a1bba6c9f83e0dac9e15a6) --- doc/openvpn.8 | 2 ++ src/openvpn/options.c | 4 ++++ src/openvpn/ssl_verify_backend.h | 8 ++++++++ src/openvpn/ssl_verify_openssl.c | 18 +++++++++++++++++- 4 files changed, 31 insertions(+), 1 deletion(-) diff --git a/doc/openvpn.8 b/doc/openvpn.8 index 284e8e628..109afe667 100644 --- a/doc/openvpn.8 +++ b/doc/openvpn.8 @@ -4981,6 +4981,8 @@ option will match against the chosen .B fieldname instead of the Common Name. +Only the subjectAltName and issuerAltName X.509 extensions are supported. + .B Please note: This option has a feature which will convert an all-lowercase .B fieldname diff --git a/src/openvpn/options.c b/src/openvpn/options.c index aff77c496..6faa28082 100644 --- a/src/openvpn/options.c +++ b/src/openvpn/options.c @@ -7023,6 +7023,10 @@ add_option (struct options *options, "configuration", p[1]); } } + else if (!x509_username_field_ext_supported(s+4)) + { + msg(msglevel, "Unsupported x509-username-field extension: %s", s); + } options->x509_username_field = p[1]; } #endif /* ENABLE_X509ALTUSERNAME */ diff --git a/src/openvpn/ssl_verify_backend.h b/src/openvpn/ssl_verify_backend.h index 488983f4d..1c8d43c41 100644 --- a/src/openvpn/ssl_verify_backend.h +++ b/src/openvpn/ssl_verify_backend.h @@ -112,6 +112,14 @@ unsigned char *x509_get_sha1_hash (openvpn_x509_cert_t *cert, struct gc_arena *g result_t backend_x509_get_username (char *common_name, int cn_len, char * x509_username_field, openvpn_x509_cert_t *peer_cert); +#ifdef ENABLE_X509ALTUSERNAME +/** + * Return true iff the supplied extension field is supported by the + * --x509-username-field option. + */ +bool x509_username_field_ext_supported(const char *extname); +#endif + /* * Return the certificate's serial number in decimal string representation. * diff --git a/src/openvpn/ssl_verify_openssl.c b/src/openvpn/ssl_verify_openssl.c index 11eb7be51..ba18e683c 100644 --- a/src/openvpn/ssl_verify_openssl.c +++ b/src/openvpn/ssl_verify_openssl.c @@ -93,14 +93,30 @@ cleanup: } #ifdef ENABLE_X509ALTUSERNAME +bool +x509_username_field_ext_supported(const char *fieldname) +{ + int nid = OBJ_txt2nid(fieldname); + return nid == NID_subject_alt_name || nid == NID_issuer_alt_name; +} + static bool extract_x509_extension(X509 *cert, char *fieldname, char *out, int size) { bool retval = false; char *buf = 0; GENERAL_NAMES *extensions; - int nid = OBJ_txt2nid(fieldname); + int nid; + + if (!x509_username_field_ext_supported(fieldname)) + { + msg(D_TLS_ERRORS, + "ERROR: --x509-alt-username field 'ext:%s' not supported", + fieldname); + return false; + } + nid = OBJ_txt2nid(fieldname); extensions = (GENERAL_NAMES *)X509_get_ext_d2i(cert, nid, NULL, NULL); if ( extensions ) { -- 2.47.2