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

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

@@ -0,0 +1,45 @@
+From bb8fa495d00ccd931eec87a01b8920636cf7903e 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)
+---
+ 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 6d244ffd4..39a504ca1 100644
+--- a/src/kdc/do_tgs_req.c
++++ b/src/kdc/do_tgs_req.c
+@@ -207,6 +207,11 @@ 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: 1.19.2
-Release: %{?zdpd}1%{?dist}
+Release: %{?zdpd}2%{?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-leaks-on-error-in-kadm5-init-functions.patch
 Patch25: Clean-up-context-after-failed-open-in-libkdb5.patch
 Patch26: Use-asan-in-one-of-the-CI-builds.patch
 Patch29: Clean-up-gssapi_krb5-ccache-name-functions.patch
+Patch30: Fix-KDC-null-deref-on-TGS-inner-body-null-server.patch
 
 License: MIT
 URL: https://web.mit.edu/kerberos/www/
@@ -651,6 +652,9 @@ exit 0
 %{_libdir}/libkadm5srv_mit.so.*
 
 %changelog
+* Thu Aug 19 2021 Robbie Harwood <rharwood@redhat.com> - 1.19.2-2
+- Fix KDC null deref on TGS inner body null server (CVE-2021-37750)
+
 * Mon Jul 26 2021 Robbie Harwood <rharwood@redhat.com> - 1.19.2-1
 - New upstream version (1.19.2)