Fix KDC null deref on TGS inner body null server (CVE-2021-37750)

Resolves: #1997602
Signed-off-by: Antonio Torres <antorres@redhat.com>

Fix-KDC-null-deref-on-TGS-inner-body-null-server.patch

@@ -0,0 +1,47 @@
+From 0a8dfc380fe3b210662ba1b1d452fcec2f84841b Mon Sep 17 00:00:00 2001
+From: Greg Hudson <ghudson@mit.edu>
+Date: Tue, 3 Aug 2021 01:15:27 -0400
+Subject: [PATCH] Fix KDC null deref on TGS inner body null server
+
+After the KDC decodes a FAST inner body, it does not check for a null
+server.  Prior to commit 39548a5b17bbda9eeb63625a201cfd19b9de1c5b this
+would typically result in an error from krb5_unparse_name(), but with
+the addition of get_local_tgt() it results in a null dereference.  Add
+a null check.
+
+Reported by Joseph Sutton of Catalyst.
+
+CVE-2021-37750:
+
+In MIT krb5 releases 1.14 and later, an authenticated attacker can
+cause a null dereference in the KDC by sending a FAST TGS request with
+no server field.
+
+ticket: 9008 (new)
+tags: pullup
+target_version: 1.19-next
+target_version: 1.18-next
+
+(cherry picked from commit d775c95af7606a51bf79547a94fa52ddd1cb7f49)
+(cherry picked from commit bb8fa495d00ccd931eec87a01b8920636cf7903e)
+(cherry picked from commit dfe383f8251d0edc7e5e08ec5e4fdd9b7f902b2a)
+---
+ src/kdc/do_tgs_req.c | 5 +++++
+ 1 file changed, 5 insertions(+)
+
+diff --git a/src/kdc/do_tgs_req.c b/src/kdc/do_tgs_req.c
+index 463a9c0dd..7c596a111 100644
+--- a/src/kdc/do_tgs_req.c
++++ b/src/kdc/do_tgs_req.c
+@@ -208,6 +208,11 @@ process_tgs_req(krb5_kdc_req *request, krb5_data *pkt,
+         status = "FIND_FAST";
+         goto cleanup;
+     }
++    if (sprinc == NULL) {
++        status = "NULL_SERVER";
++        errcode = KRB5KDC_ERR_S_PRINCIPAL_UNKNOWN;
++        goto cleanup;
++    }
+ 
+     errcode = get_local_tgt(kdc_context, &sprinc->realm, header_server,
+                             &local_tgt, &local_tgt_storage, &local_tgt_key);

krb5.spec

@@ -42,7 +42,7 @@
 Summary: The Kerberos network authentication system
 Name: krb5
 Version: 1.19.1
-Release: %{?zdpd}11%{?dist}.1
+Release: %{?zdpd}12%{?dist}
 
 # rharwood has trust path to signing key and verifies on check-in
 Source0: https://web.mit.edu/kerberos/dist/krb5/%{version}/krb5-%{version}%{?dashpre}.tar.gz
@@ -89,6 +89,7 @@ Patch24: Fix-some-principal-realm-canonicalization-cases.patch
 Patch25: Allow-kinit-with-keytab-to-defer-canonicalization.patch
 Patch26: Fix-kadmin-k-with-fallback-or-referral-realm.patch
 Patch27: Fix-KDC-null-deref-on-bad-encrypted-challenge.patch
+Patch28: Fix-KDC-null-deref-on-TGS-inner-body-null-server.patch
 
 License: MIT
 URL: https://web.mit.edu/kerberos/www/
@@ -650,6 +651,10 @@ exit 0
 %{_libdir}/libkadm5srv_mit.so.*
 
 %changelog
+* Wed Oct 20 2021 Antonio Torres <antorres@redhat.com> - 1.19.1-12
+- Fix KDC null deref on TGS inner body null server (CVE-2021-37750)
+- Resolves: #1997602
+
 * Mon Aug 09 2021 Mohan Boddu <mboddu@redhat.com> - 1.19.1-11.1
 - Rebuilt for IMA sigs, glibc 2.34, aarch64 flags
   Related: rhbz#1991688