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From 2a96564f6fd53f2e1e8424d865c02349bfe5b818 Mon Sep 17 00:00:00 2001
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From: Isaac Boukris <iboukris@gmail.com>
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Date: Sat, 15 Dec 2018 11:56:36 +0200
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Subject: [PATCH] Remove incorrect KDC assertion
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The assertion in return_enc_padata() is reachable because
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kdc_make_s4u2self_rep() may have previously added encrypted padata.
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It is no longer necessary because the code uses add_pa_data_element()
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instead of allocating a new list.
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CVE-2018-20217:
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In MIT krb5 1.8 or later, an authenticated user who can obtain a TGT
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using an older encryption type (DES, DES3, or RC4) can cause an
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assertion failure in the KDC by sending an S4U2Self request.
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[ghudson@mit.edu: rewrote commit message with CVE description]
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(cherry picked from commit 94e5eda5bb94d1d44733a49c3d9b6d1e42c74def)
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ticket: 8767
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version_fixed: 1.16.3
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(cherry picked from commit 56870f9456da78d77a667dfc03a6d90f948dc3a5)
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---
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src/kdc/kdc_preauth.c | 1 -
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src/tests/gssapi/t_s4u.py | 7 +++++++
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2 files changed, 7 insertions(+), 1 deletion(-)
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diff --git a/src/kdc/kdc_preauth.c b/src/kdc/kdc_preauth.c
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index 811c16368..6f0cf68d9 100644
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--- a/src/kdc/kdc_preauth.c
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+++ b/src/kdc/kdc_preauth.c
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@@ -1666,7 +1666,6 @@ return_enc_padata(krb5_context context, krb5_data *req_pkt,
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krb5_error_code code = 0;
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/* This should be initialized and only used for Win2K compat and other
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* specific standardized uses such as FAST negotiation. */
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- assert(reply_encpart->enc_padata == NULL);
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if (is_referral) {
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code = return_referral_enc_padata(context, reply_encpart, server);
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if (code)
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diff --git a/src/tests/gssapi/t_s4u.py b/src/tests/gssapi/t_s4u.py
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index fc9d9e8a4..f65000453 100755
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--- a/src/tests/gssapi/t_s4u.py
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+++ b/src/tests/gssapi/t_s4u.py
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@@ -139,6 +139,13 @@ if 'auth1: user@' not in out or 'auth2: user@' not in out:
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realm.stop()
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+for realm in multipass_realms(create_host=False, get_creds=False):
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+ service1 = 'service/1@%s' % realm.realm
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+ realm.addprinc(service1)
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+ realm.extract_keytab(service1, realm.keytab)
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+ realm.kinit(service1, None, ['-k'])
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+ realm.run(['./t_s4u', 'p:user', '-'])
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+
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# Exercise cross-realm S4U2Self. The query in the foreign realm will
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# fail, but we can check that the right server principal was used.
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r1, r2 = cross_realms(2, create_user=False)
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