Remove incorrect KDC assertion

The assertion in return_enc_padata() is reachable because
kdc_make_s4u2self_rep() may have previously added encrypted padata.
It is no longer necessary because the code uses add_pa_data_element()
instead of allocating a new list.

CVE-2018-20217:

In MIT krb5 1.8 or later, an authenticated user who can obtain a TGT
using an older encryption type (DES, DES3, or RC4) can cause an
assertion failure in the KDC by sending an S4U2Self request.

[ghudson@mit.edu: rewrote commit message with CVE description]

ticket: 8767 (new)
tags: pullup
target_version: 1.17
target_version: 1.16-next
target_version: 1.15-next

diff --git a/src/kdc/kdc_preauth.c b/src/kdc/kdc_preauth.c
index 74953c99fa559cd1eab12698437a93c207c63a12..caf133c14da7f68fe0e6d1c2500e60184338d273 100644 (file)
--- a/src/kdc/kdc_preauth.c
+++ b/src/kdc/kdc_preauth.c
@@ -1683,7 +1683,6 @@ return_enc_padata(krb5_context context, krb5_data *req_pkt,
     krb5_error_code code = 0;
     /* This should be initialized and only used for Win2K compat and other
      * specific standardized uses such as FAST negotiation. */
-    assert(reply_encpart->enc_padata == NULL);
     if (is_referral) {
         code = return_referral_enc_padata(context, reply_encpart, server);
         if (code)

diff --git a/src/tests/gssapi/t_s4u.py b/src/tests/gssapi/t_s4u.py
index 84f3fbd752b897e95580fe75cf49310a4b1c48f0..164fec862e196711bb5f5b59cd18acf5bc398b61 100755 (executable)
--- a/src/tests/gssapi/t_s4u.py
+++ b/src/tests/gssapi/t_s4u.py
@@ -147,6 +147,14 @@ if 'auth1: user@' not in out or 'auth2: user@' not in out:
 
 realm.stop()
 
+mark('S4U2Self with various enctypes')
+for realm in multipass_realms(create_host=False, get_creds=False):
+    service1 = 'service/1@%s' % realm.realm
+    realm.addprinc(service1)
+    realm.extract_keytab(service1, realm.keytab)
+    realm.kinit(service1, None, ['-k'])
+    realm.run(['./t_s4u', 'e:user', '-'])
+
 # Test cross realm S4U2Self using server referrals.
 mark('cross-realm S4U2Self')
 testprincs = {'krbtgt/SREALM': {'keys': 'aes128-cts'},