From d775c95af7606a51bf79547a94fa52ddd1cb7f49 Mon Sep 17 00:00:00 2001 From: Greg Hudson 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 --- 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 582e497cc9..32dc65fa8e 100644 --- a/src/kdc/do_tgs_req.c +++ b/src/kdc/do_tgs_req.c @@ -204,6 +204,11 @@ 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);