From ff388043f1a790a897f21e9d3aac2474d040415b Mon Sep 17 00:00:00 2001 From: Robbie Harwood Date: Thu, 14 Jun 2018 17:45:09 -0400 Subject: [PATCH] Add flag to disable encrypted timestamp on client --- ...isable-encrypted-timestamp-on-client.patch | 204 ++++++++++++++++++ krb5.spec | 6 +- 2 files changed, 209 insertions(+), 1 deletion(-) create mode 100644 Add-flag-to-disable-encrypted-timestamp-on-client.patch diff --git a/Add-flag-to-disable-encrypted-timestamp-on-client.patch b/Add-flag-to-disable-encrypted-timestamp-on-client.patch new file mode 100644 index 0000000..adc4f41 --- /dev/null +++ b/Add-flag-to-disable-encrypted-timestamp-on-client.patch @@ -0,0 +1,204 @@ +From f44ef4893050e673f495444c27a19525813f75a8 Mon Sep 17 00:00:00 2001 +From: Greg Hudson +Date: Mon, 11 Jun 2018 13:53:27 -0400 +Subject: [PATCH] Add flag to disable encrypted timestamp on client + +ticket: 8655 +(cherry picked from commit 4ad376134b8d456392edbac7a7d351e6c7a7f0e7) +--- + doc/admin/conf_files/krb5_conf.rst | 10 ++++++++++ + doc/admin/spake.rst | 8 ++++++++ + src/include/k5-int.h | 1 + + src/include/k5-trace.h | 2 ++ + src/lib/krb5/krb/get_in_tkt.c | 23 +++++++++++++++++++++++ + src/lib/krb5/krb/init_creds_ctx.h | 1 + + src/lib/krb5/krb/preauth_encts.c | 14 +++++++++++++- + src/tests/t_referral.py | 13 +++++++++++++ + 8 files changed, 71 insertions(+), 1 deletion(-) + +diff --git a/doc/admin/conf_files/krb5_conf.rst b/doc/admin/conf_files/krb5_conf.rst +index ce545492d..eb5c29e5d 100644 +--- a/doc/admin/conf_files/krb5_conf.rst ++++ b/doc/admin/conf_files/krb5_conf.rst +@@ -475,6 +475,16 @@ following tags may be specified in the realm's subsection: + (for example, when converting ``rcmd.hostname`` to + ``host/hostname.domain``). + ++**disable_encrypted_timestamp** ++ If this flag is true, the client will not perform encrypted ++ timestamp preauthentication if requested by the KDC. Setting this ++ flag can help to prevent dictionary attacks by active attackers, ++ if the realm's KDCs support SPAKE preauthentication or if initial ++ authentication always uses another mechanism or always uses FAST. ++ This flag persists across client referrals during initial ++ authentication. This flag does not prevent the KDC from offering ++ encrypted timestamp. New in release 1.17. ++ + **http_anchors** + When KDCs and kpasswd servers are accessed through HTTPS proxies, this tag + can be used to specify the location of the CA certificate which should be +diff --git a/doc/admin/spake.rst b/doc/admin/spake.rst +index b65c694aa..4f6eeaf53 100644 +--- a/doc/admin/spake.rst ++++ b/doc/admin/spake.rst +@@ -30,6 +30,14 @@ principal entries, as you would for any preauthentication mechanism:: + Clients which do not implement SPAKE preauthentication will fall back + to encrypted timestamp. + ++An active attacker can force a fallback to encrypted timestamp by ++modifying the initial KDC response, defeating the protection against ++dictionary attacks. To prevent this fallback on clients which do ++implement SPAKE preauthentication, set the ++**disable_encrypted_timestamp** variable to ``true`` in the ++:ref:`realms` subsection for realms whose KDCs offer SPAKE ++preauthentication. ++ + By default, SPAKE preauthentication requires an extra network round + trip to the KDC during initial authentication. If most of the clients + in a realm support SPAKE, this extra round trip can be eliminated +diff --git a/src/include/k5-int.h b/src/include/k5-int.h +index 86b53c76b..e4a9a1412 100644 +--- a/src/include/k5-int.h ++++ b/src/include/k5-int.h +@@ -204,6 +204,7 @@ typedef unsigned char u_char; + #define KRB5_CONF_DES_CRC_SESSION_SUPPORTED "des_crc_session_supported" + #define KRB5_CONF_DICT_FILE "dict_file" + #define KRB5_CONF_DISABLE "disable" ++#define KRB5_CONF_DISABLE_ENCRYPTED_TIMESTAMP "disable_encrypted_timestamp" + #define KRB5_CONF_DISABLE_LAST_SUCCESS "disable_last_success" + #define KRB5_CONF_DISABLE_LOCKOUT "disable_lockout" + #define KRB5_CONF_DNS_CANONICALIZE_HOSTNAME "dns_canonicalize_hostname" +diff --git a/src/include/k5-trace.h b/src/include/k5-trace.h +index 5f7eb9517..0854974dc 100644 +--- a/src/include/k5-trace.h ++++ b/src/include/k5-trace.h +@@ -299,6 +299,8 @@ void krb5int_trace(krb5_context context, const char *fmt, ...); + #define TRACE_PREAUTH_ENC_TS(c, sec, usec, plain, enc) \ + TRACE(c, "Encrypted timestamp (for {long}.{int}): plain {hexdata}, " \ + "encrypted {hexdata}", (long) sec, (int) usec, plain, enc) ++#define TRACE_PREAUTH_ENC_TS_DISABLED(c) \ ++ TRACE(c, "Ignoring encrypted timestamp because it is disabled") + #define TRACE_PREAUTH_ETYPE_INFO(c, etype, salt, s2kparams) \ + TRACE(c, "Selected etype info: etype {etype}, salt \"{data}\", " \ + "params \"{data}\"", etype, salt, s2kparams) +diff --git a/src/lib/krb5/krb/get_in_tkt.c b/src/lib/krb5/krb/get_in_tkt.c +index c026bbc6d..79dede2c6 100644 +--- a/src/lib/krb5/krb/get_in_tkt.c ++++ b/src/lib/krb5/krb/get_in_tkt.c +@@ -801,6 +801,24 @@ read_allowed_preauth_type(krb5_context context, krb5_init_creds_context ctx) + free(tmp); + } + ++/* Return true if encrypted timestamp is disabled for realm. */ ++static krb5_boolean ++encts_disabled(profile_t profile, const krb5_data *realm) ++{ ++ krb5_error_code ret; ++ char *realmstr; ++ int bval; ++ ++ realmstr = k5memdup0(realm->data, realm->length, &ret); ++ if (realmstr == NULL) ++ return FALSE; ++ ret = profile_get_boolean(profile, KRB5_CONF_REALMS, realmstr, ++ KRB5_CONF_DISABLE_ENCRYPTED_TIMESTAMP, FALSE, ++ &bval); ++ free(realmstr); ++ return (ret == 0) ? bval : FALSE; ++} ++ + /** + * Throw away any pre-authentication realm state and begin with a + * unauthenticated or optimistically authenticated request. If fast_upgrade is +@@ -842,6 +860,11 @@ restart_init_creds_loop(krb5_context context, krb5_init_creds_context ctx, + goto cleanup; + } + ++ /* Never set encts_disabled back to false, so it can't be circumvented with ++ * client realm referrals. */ ++ if (encts_disabled(context->profile, &ctx->request->client->realm)) ++ ctx->encts_disabled = TRUE; ++ + krb5_free_principal(context, ctx->request->server); + ctx->request->server = NULL; + +diff --git a/src/lib/krb5/krb/init_creds_ctx.h b/src/lib/krb5/krb/init_creds_ctx.h +index 7ba61e17c..7a6219b1c 100644 +--- a/src/lib/krb5/krb/init_creds_ctx.h ++++ b/src/lib/krb5/krb/init_creds_ctx.h +@@ -61,6 +61,7 @@ struct _krb5_init_creds_context { + krb5_boolean info_pa_permitted; + krb5_boolean restarted; + krb5_boolean fallback_disabled; ++ krb5_boolean encts_disabled; + struct krb5_responder_context_st rctx; + krb5_preauthtype selected_preauth_type; + krb5_preauthtype allowed_preauth_type; +diff --git a/src/lib/krb5/krb/preauth_encts.c b/src/lib/krb5/krb/preauth_encts.c +index 45bf9da92..345701984 100644 +--- a/src/lib/krb5/krb/preauth_encts.c ++++ b/src/lib/krb5/krb/preauth_encts.c +@@ -28,6 +28,7 @@ + #include + #include + #include "int-proto.h" ++#include "init_creds_ctx.h" + + static krb5_error_code + encts_prep_questions(krb5_context context, krb5_clpreauth_moddata moddata, +@@ -38,7 +39,10 @@ encts_prep_questions(krb5_context context, krb5_clpreauth_moddata moddata, + krb5_data *encoded_previous_request, + krb5_pa_data *pa_data) + { +- cb->need_as_key(context, rock); ++ krb5_init_creds_context ctx = (krb5_init_creds_context)rock; ++ ++ if (!ctx->encts_disabled) ++ cb->need_as_key(context, rock); + return 0; + } + +@@ -51,6 +55,7 @@ encts_process(krb5_context context, krb5_clpreauth_moddata moddata, + krb5_prompter_fct prompter, void *prompter_data, + krb5_pa_data ***out_padata) + { ++ krb5_init_creds_context ctx = (krb5_init_creds_context)rock; + krb5_error_code ret; + krb5_pa_enc_ts pa_enc; + krb5_data *ts = NULL, *enc_ts = NULL; +@@ -60,6 +65,13 @@ encts_process(krb5_context context, krb5_clpreauth_moddata moddata, + + enc_data.ciphertext = empty_data(); + ++ if (ctx->encts_disabled) { ++ TRACE_PREAUTH_ENC_TS_DISABLED(context); ++ k5_setmsg(context, KRB5_PREAUTH_FAILED, ++ _("Encrypted timestamp is disabled")); ++ return KRB5_PREAUTH_FAILED; ++ } ++ + ret = cb->get_as_key(context, rock, &as_key); + if (ret) + goto cleanup; +diff --git a/src/tests/t_referral.py b/src/tests/t_referral.py +index 98fdf2925..e12fdc2e9 100755 +--- a/src/tests/t_referral.py ++++ b/src/tests/t_referral.py +@@ -126,4 +126,17 @@ r1.klist('user@KRBTEST2.COM', 'krbtgt/KRBTEST2.COM') + r1.kinit('abc@XYZ', 'pw', ['-E']) + r1.klist('abc\@XYZ@KRBTEST2.COM', 'krbtgt/KRBTEST2.COM') + ++# Test that disable_encrypted_timestamp persists across client ++# referrals. (This test relies on SPAKE not being enabled by default ++# on the KDC.) ++r2.run([kadminl, 'modprinc', '+preauth', 'user']) ++msgs = ('Encrypted timestamp (for ') ++r1.kinit('user', password('user'), ['-C'], expected_trace=msgs) ++dconf = {'realms': {'$realm': {'disable_encrypted_timestamp': 'true'}}} ++denv = r1.special_env('disable_encts', False, krb5_conf=dconf) ++msgs = ('Ignoring encrypted timestamp because it is disabled', ++ '/Encrypted timestamp is disabled') ++r1.kinit('user', None, ['-C'], env=denv, expected_code=1, expected_trace=msgs, ++ expected_msg='Encrypted timestamp is disabled') ++ + success('KDC host referral tests') diff --git a/krb5.spec b/krb5.spec index 7dbcdaf..e1681e2 100644 --- a/krb5.spec +++ b/krb5.spec @@ -18,7 +18,7 @@ Summary: The Kerberos network authentication system Name: krb5 Version: 1.16.1 # for prerelease, should be e.g., 0.% {prerelease}.1% { ?dist } (without spaces) -Release: 6%{?dist} +Release: 7%{?dist} # lookaside-cached sources; two downloads and a build artifact Source0: https://web.mit.edu/kerberos/dist/krb5/1.16/krb5-%{version}%{prerelease}.tar.gz @@ -91,6 +91,7 @@ Patch71: Log-when-non-root-ksu-authorization-fails.patch Patch72: Add-k5_dir_filenames-to-libkrb5support.patch Patch73: Process-profile-includedir-in-sorted-order.patch Patch74: Make-docs-build-python3-compatible.patch +Patch75: Add-flag-to-disable-encrypted-timestamp-on-client.patch License: MIT URL: http://web.mit.edu/kerberos/www/ @@ -742,6 +743,9 @@ exit 0 %{_libdir}/libkadm5srv_mit.so.* %changelog +* Thu Jun 14 2018 Robbie Harwood - 1.16.1-7 +- Add flag to disable encrypted timestamp on client + * Thu Jun 14 2018 Robbie Harwood - 1.16.1-6 - Switch to python3-sphinx for docs - Resolves: #1590928