From c3a7065d5bec0ca4ad479e27c124e74fbd7c2234 Mon Sep 17 00:00:00 2001 From: Arne Schwabe Date: Sun, 21 Mar 2021 15:33:53 +0100 Subject: [PATCH] Implement peer-fingerprint to check fingerprint of peer certificate This option allows to pin one or more more peer certificates. It also prepares for doing TLS authentication without a CA and just self-signed certificates. Patch V2: Allow peer-fingerprint to be specified multiple times to allow multiple peers without needing to use inline syntax. (e.g. on command line). Patch V3: rebase on v3 of 1/4, reword message of verify-hash and peer-fingerpring incompatibility Signed-off-by: Arne Schwabe Acked-by: Antonio Quartulli Message-Id: <20210321143353.2677-1-arne@rfc2549.org> URL: https://www.mail-archive.com/search?l=mid&q=20210321143353.2677-1-arne@rfc2549.org Signed-off-by: Gert Doering --- Changes.rst | 6 +++++ doc/man-sections/inline-files.rst | 4 +-- doc/man-sections/tls-options.rst | 22 +++++++++++++++- src/openvpn/init.c | 1 + src/openvpn/options.c | 42 +++++++++++++++++++++++-------- src/openvpn/options.h | 1 + src/openvpn/ssl_common.h | 1 + src/openvpn/ssl_verify.c | 19 ++++++++------ 8 files changed, 74 insertions(+), 22 deletions(-) diff --git a/Changes.rst b/Changes.rst index d6be10502..c0e0d5d97 100644 --- a/Changes.rst +++ b/Changes.rst @@ -19,6 +19,12 @@ Compatibility with OpenSSL in FIPS mode and if less than 100MB RAM are available, use setrlimit() to upgrade the limit. See Trac #1390. Not available on OpenSolaris. +Certificate pinning/verify peer fingerprint + The ``--peer-fingerprint`` option has been introduced to give users an + easy to use alternative to the ``tls-verify`` for matching the + fingerprint of the peer. The option takes use a number of allowed + SHA256 certificate fingerprints. + Deprecated features ------------------- diff --git a/doc/man-sections/inline-files.rst b/doc/man-sections/inline-files.rst index 303bb3c8a..01e4a8406 100644 --- a/doc/man-sections/inline-files.rst +++ b/doc/man-sections/inline-files.rst @@ -4,8 +4,8 @@ INLINE FILE SUPPORT OpenVPN allows including files in the main configuration for the ``--ca``, ``--cert``, ``--dh``, ``--extra-certs``, ``--key``, ``--pkcs12``, ``--secret``, ``--crl-verify``, ``--http-proxy-user-pass``, ``--tls-auth``, -``--auth-gen-token-secret``, ``--tls-crypt``, ``--tls-crypt-v2`` and -``--verify-hash`` options. +``--auth-gen-token-secret``, ``--peer-fingerprint``, ``--tls-crypt``, +``--tls-crypt-v2`` and ``--verify-hash`` options. Each inline file started by the line ```` diff --git a/doc/man-sections/tls-options.rst b/doc/man-sections/tls-options.rst index d8f9800e7..cfe1ec98a 100644 --- a/doc/man-sections/tls-options.rst +++ b/doc/man-sections/tls-options.rst @@ -271,7 +271,8 @@ certificates and keys: https://github.com/OpenVPN/easy-rsa man-in-the-middle attack where an authorized client attempts to connect to another client by impersonating the server. The attack is easily prevented by having clients verify the server certificate using any one - of ``--remote-cert-tls``, ``--verify-x509-name``, or ``--tls-verify``. + of ``--remote-cert-tls``, ``--verify-x509-name``, ``--peer-fingerprint`` + or ``--tls-verify``. --tls-auth args Add an additional layer of HMAC authentication on top of the TLS control @@ -592,6 +593,25 @@ certificates and keys: https://github.com/OpenVPN/easy-rsa If the option is inlined, ``algo`` is always :code:`SHA256`. +--peer-fingerprint args + Specify a SHA256 fingerprint or list of SHA256 fingerprints to verify + the peer certificate against. The peer certificate must match one of the + fingerprint or certificate verification will fail. The option can also + be inlined + + Valid syntax: + :: + + peer-fingerprint AD:B0:95:D8:09:... + + or inline: + :: + + + 00:11:22:33:44:55:66:77:88:99:aa:bb:cc:dd:ee:ff:00:11:22:33:44:55:66:77:88:99:aa:bb:cc:dd:ee:ff + 11:22:33:44:55:66:77:88:99:aa:bb:cc:dd:ee:ff:00:11:22:33:44:55:66:77:88:99:aa:bb:cc:dd:ee:ff:00 + + --verify-x509-name args Accept connections only if a host's X.509 name is equal to **name.** The remote host must also pass all other tests of verification. diff --git a/src/openvpn/init.c b/src/openvpn/init.c index d234729c6..731b0cf2b 100644 --- a/src/openvpn/init.c +++ b/src/openvpn/init.c @@ -2927,6 +2927,7 @@ do_init_crypto_tls(struct context *c, const unsigned int flags) to.remote_cert_eku = options->remote_cert_eku; to.verify_hash = options->verify_hash; to.verify_hash_algo = options->verify_hash_algo; + to.verify_hash_depth = options->verify_hash_depth; #ifdef ENABLE_X509ALTUSERNAME memcpy(to.x509_username_field, options->x509_username_field, sizeof(to.x509_username_field)); #else diff --git a/src/openvpn/options.c b/src/openvpn/options.c index d1ff4e089..38ced536d 100644 --- a/src/openvpn/options.c +++ b/src/openvpn/options.c @@ -8117,26 +8117,45 @@ add_option(struct options *options, options->extra_certs_file = p[1]; options->extra_certs_file_inline = is_inline; } - else if (streq(p[0], "verify-hash") && p[1] && !p[3]) + else if ((streq(p[0], "verify-hash") && p[1] && !p[3]) + || (streq(p[0], "peer-fingerprint") && p[1] && !p[2])) { VERIFY_PERMISSION(OPT_P_GENERAL|OPT_P_INLINE); + + int verify_hash_depth = 0; + if (streq(p[0], "verify-hash")) + { + /* verify level 1 cert, i.e. the CA that signed the leaf cert */ + verify_hash_depth = 1; + } + options->verify_hash_algo = MD_SHA256; int digest_len = SHA256_DIGEST_LENGTH; - if ((!p[2] && !is_inline) || (p[2] && streq(p[2], "SHA1"))) + if (options->verify_hash && options->verify_hash_depth != verify_hash_depth) { - options->verify_hash_algo = MD_SHA1; - msg(M_WARN, "DEPRECATED FEATURE: Usage of SHA1 fingerprints for " - "verify-hash is deprecated. You should switch to SHA256."); - options->verify_hash_algo = MD_SHA1; - digest_len = SHA_DIGEST_LENGTH; + msg(msglevel, "ERROR: Setting %s not allowed. --verify-hash and" + " --peer-fingerprint are mutually exclusive", p[0]); + goto err; } - else if (p[2] && !streq(p[2], "SHA256")) + + if (streq(p[0], "verify-hash")) { - msg(msglevel, "invalid or unsupported hashing algorithm: %s " - "(only SHA1 and SHA256 are valid)", p[2]); - goto err; + if ((!p[2] && !is_inline) || (p[2] && streq(p[2], "SHA1"))) + { + options->verify_hash_algo = MD_SHA1; + msg(M_WARN, "DEPRECATED FEATURE: Usage of SHA1 fingerprints for " + "verify-hash is deprecated. You should switch to SHA256."); + options->verify_hash_algo = SHA_DIGEST_LENGTH; + digest_len = SHA_DIGEST_LENGTH; + } + else if (p[2] && !streq(p[2], "SHA256")) + { + msg(msglevel, "invalid or unsupported hashing algorithm: %s " + "(only SHA1 and SHA256 are supported)", p[2]); + goto err; + } } struct verify_hash_list *newlist; @@ -8147,6 +8166,7 @@ add_option(struct options *options, if (!options->verify_hash) { options->verify_hash = newlist; + options->verify_hash_depth = verify_hash_depth; } else { diff --git a/src/openvpn/options.h b/src/openvpn/options.h index a7b3174f5..30ec53d67 100644 --- a/src/openvpn/options.h +++ b/src/openvpn/options.h @@ -560,6 +560,7 @@ struct options const char *remote_cert_eku; struct verify_hash_list *verify_hash; hash_algo_type verify_hash_algo; + int verify_hash_depth; unsigned int ssl_flags; /* set to SSLF_x flags from ssl.h */ #ifdef ENABLE_PKCS11 diff --git a/src/openvpn/ssl_common.h b/src/openvpn/ssl_common.h index f6aaae98f..2b1b87fb8 100644 --- a/src/openvpn/ssl_common.h +++ b/src/openvpn/ssl_common.h @@ -284,6 +284,7 @@ struct tls_options unsigned remote_cert_ku[MAX_PARMS]; const char *remote_cert_eku; struct verify_hash_list *verify_hash; + int verify_hash_depth; hash_algo_type verify_hash_algo; #ifdef ENABLE_X509ALTUSERNAME char *x509_username_field[MAX_PARMS]; diff --git a/src/openvpn/ssl_verify.c b/src/openvpn/ssl_verify.c index 06de0f5ff..923eac919 100644 --- a/src/openvpn/ssl_verify.c +++ b/src/openvpn/ssl_verify.c @@ -721,19 +721,18 @@ verify_cert(struct tls_session *session, openvpn_x509_cert_t *cert, int cert_dep goto cleanup; /* Reject connection */ } - /* verify level 1 cert, i.e. the CA that signed our leaf cert */ - if (cert_depth == 1 && opt->verify_hash) + if (cert_depth == opt->verify_hash_depth && opt->verify_hash) { - struct buffer ca_hash = {0}; + struct buffer cert_fp = {0}; switch (opt->verify_hash_algo) { case MD_SHA1: - ca_hash = x509_get_sha1_fingerprint(cert, &gc); + cert_fp = x509_get_sha1_fingerprint(cert, &gc); break; case MD_SHA256: - ca_hash = x509_get_sha256_fingerprint(cert, &gc); + cert_fp = x509_get_sha256_fingerprint(cert, &gc); break; default: @@ -752,8 +751,8 @@ verify_cert(struct tls_session *session, openvpn_x509_cert_t *cert, int cert_dep while (current_hash) { - if (memcmp_constant_time(BPTR(&ca_hash), current_hash->hash, - BLEN(&ca_hash)) == 0) + if (memcmp_constant_time(BPTR(&cert_fp), current_hash->hash, + BLEN(&cert_fp)) == 0) { break; } @@ -762,7 +761,11 @@ verify_cert(struct tls_session *session, openvpn_x509_cert_t *cert, int cert_dep if (!current_hash) { - msg(D_TLS_ERRORS, "TLS Error: --tls-verify certificate hash verification failed"); + const char *hex_fp = format_hex_ex(BPTR(&cert_fp), BLEN(&cert_fp), + 0, 1, ":", &gc); + msg(D_TLS_ERRORS, "TLS Error: --tls-verify/--peer-fingerprint" + "certificate hash verification failed. (got " + "fingerprint: %s", hex_fp); goto cleanup; } } -- 2.47.2