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From fc98f520caefff2e5ee9a0026fdf5109944b3562 Mon Sep 17 00:00:00 2001
From: Joseph Sutton <josephsutton@catalyst.net.nz>
Date: Wed, 7 Jul 2021 11:47:44 +1200
Subject: [PATCH] Fix KDC null deref on bad encrypted challenge
The function ec_verify() in src/kdc/kdc_preauth_ec.c contains a check
to avoid further processing if the armor key is NULL. However, this
check is bypassed by a call to k5memdup0() which overwrites retval
with 0 if the allocation succeeds. If the armor key is NULL, a call
to krb5_c_fx_cf2_simple() will then dereference it, resulting in a
crash. Add a check before the k5memdup0() call to avoid overwriting
retval.
CVE-2021-36222:
In MIT krb5 releases 1.16 and later, an unauthenticated attacker can
cause a null dereference in the KDC by sending a request containing a
PA-ENCRYPTED-CHALLENGE padata element without using FAST.
[ghudson@mit.edu: trimmed patch; added test case; edited commit
message]
ticket: 9007 (new)
tags: pullup
target_version: 1.19-next
target_version: 1.18-next
CVE: CVE-2021-36222
Upstream-Status: Backport
[https://github.com/krb5/krb5/commit/fc98f520caefff2e5ee9a0026fdf5109944b3562]
Signed-off-by: Yi Zhao <yi.zhao@windriver.com>
---
src/kdc/kdc_preauth_ec.c | 3 ++-
src/tests/Makefile.in | 1 +
src/tests/t_cve-2021-36222.py | 46 +++++++++++++++++++++++++++++++++++
3 files changed, 49 insertions(+), 1 deletion(-)
create mode 100644 src/tests/t_cve-2021-36222.py
diff --git a/src/kdc/kdc_preauth_ec.c b/src/kdc/kdc_preauth_ec.c
index 7e636b3f9..43a9902cc 100644
--- a/src/kdc/kdc_preauth_ec.c
+++ b/src/kdc/kdc_preauth_ec.c
@@ -87,7 +87,8 @@ ec_verify(krb5_context context, krb5_data *req_pkt, krb5_kdc_req *request,
}
/* Check for a configured FAST ec auth indicator. */
- realmstr = k5memdup0(realm.data, realm.length, &retval);
+ if (retval == 0)
+ realmstr = k5memdup0(realm.data, realm.length, &retval);
if (realmstr != NULL)
retval = profile_get_string(context->profile, KRB5_CONF_REALMS,
realmstr,
diff --git a/src/tests/Makefile.in b/src/tests/Makefile.in
index fc6fcc0c3..1a1938306 100644
--- a/src/tests/Makefile.in
+++ b/src/tests/Makefile.in
@@ -166,6 +166,7 @@ check-pytests: unlockiter s4u2self
$(RUNPYTEST) $(srcdir)/t_cve-2012-1015.py $(PYTESTFLAGS)
$(RUNPYTEST) $(srcdir)/t_cve-2013-1416.py $(PYTESTFLAGS)
$(RUNPYTEST) $(srcdir)/t_cve-2013-1417.py $(PYTESTFLAGS)
+ $(RUNPYTEST) $(srcdir)/t_cve-2021-36222.py $(PYTESTFLAGS)
$(RM) au.log
$(RUNPYTEST) $(srcdir)/t_audit.py $(PYTESTFLAGS)
$(RUNPYTEST) $(srcdir)/jsonwalker.py -d $(srcdir)/au_dict.json \
diff --git a/src/tests/t_cve-2021-36222.py b/src/tests/t_cve-2021-36222.py
new file mode 100644
index 000000000..57e04993b
--- /dev/null
+++ b/src/tests/t_cve-2021-36222.py
@@ -0,0 +1,46 @@
+import socket
+from k5test import *
+
+realm = K5Realm()
+
+# CVE-2021-36222 KDC null dereference on encrypted challenge preauth
+# without FAST
+
+s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
+a = (hostname, realm.portbase)
+
+m = ('6A81A0' '30819D' # [APPLICATION 10] SEQUENCE
+ 'A103' '0201' '05' # [1] pvno = 5
+ 'A203' '0201' '0A' # [2] msg-type = 10
+ 'A30E' '300C' # [3] padata = SEQUENCE OF
+ '300A' # SEQUENCE
+ 'A104' '0202' '008A' # [1] padata-type = PA-ENCRYPTED-CHALLENGE
+ 'A202' '0400' # [2] padata-value = ""
+ 'A48180' '307E' # [4] req-body = SEQUENCE
+ 'A007' '0305' '0000000000' # [0] kdc-options = 0
+ 'A120' '301E' # [1] cname = SEQUENCE
+ 'A003' '0201' '01' # [0] name-type = NT-PRINCIPAL
+ 'A117' '3015' # [1] name-string = SEQUENCE-OF
+ '1B06' '6B7262746774' # krbtgt
+ '1B0B' '4B5242544553542E434F4D'
+ # KRBTEST.COM
+ 'A20D' '1B0B' '4B5242544553542E434F4D'
+ # [2] realm = KRBTEST.COM
+ 'A320' '301E' # [3] sname = SEQUENCE
+ 'A003' '0201' '01' # [0] name-type = NT-PRINCIPAL
+ 'A117' '3015' # [1] name-string = SEQUENCE-OF
+ '1B06' '6B7262746774' # krbtgt
+ '1B0B' '4B5242544553542E434F4D'
+ # KRBTEST.COM
+ 'A511' '180F' '31393934303631303036303331375A'
+ # [5] till = 19940610060317Z
+ 'A703' '0201' '00' # [7] nonce = 0
+ 'A808' '3006' # [8] etype = SEQUENCE OF
+ '020112' '020111') # aes256-cts aes128-cts
+
+s.sendto(bytes.fromhex(m), a)
+
+# Make sure kinit still works.
+realm.kinit(realm.user_princ, password('user'))
+
+success('CVE-2021-36222 regression test')
--
2.25.1
|
