From: Stefan Metzmacher <metze@samba.org>
Date: Wed, 20 Apr 2016 09:26:57 +0000 (+0200)
Subject: CVE-2016-2019: libcli/smb: don't allow guest sessions if we require signing
X-Git-Tag: samba-4.3.11~4
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=559a1306d813d3f11de9fdaa5850638c62ed2d79;p=thirdparty%2Fsamba.git

CVE-2016-2019: libcli/smb: don't allow guest sessions if we require signing

Note real anonymous sessions (with "" as username) don't hit this
as we don't even call smb2cli_session_set_session_key() in that case.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=11860

Signed-off-by: Stefan Metzmacher <metze@samba.org>
---

diff --git a/libcli/smb/smbXcli_base.c b/libcli/smb/smbXcli_base.c
index 419a2c09163..4039e86b36b 100644
--- a/libcli/smb/smbXcli_base.c
+++ b/libcli/smb/smbXcli_base.c
@@ -5313,6 +5313,10 @@ bool smbXcli_session_is_guest(struct smbXcli_session *session)
 		return false;
 	}
 
+	if (session->conn->mandatory_signing) {
+		return false;
+	}
+
 	if (session->conn->protocol >= PROTOCOL_SMB2_02) {
 		if (session->smb2->session_flags & SMB2_SESSION_FLAG_IS_GUEST) {
 			return true;
@@ -5567,7 +5571,7 @@ NTSTATUS smb2cli_session_set_session_key(struct smbXcli_session *session,
 					 const struct iovec *recv_iov)
 {
 	struct smbXcli_conn *conn = session->conn;
-	uint16_t no_sign_flags;
+	uint16_t no_sign_flags = 0;
 	uint8_t session_key[16];
 	bool check_signature = true;
 	uint32_t hdr_flags;
@@ -5592,7 +5596,18 @@ NTSTATUS smb2cli_session_set_session_key(struct smbXcli_session *session,
 		return NT_STATUS_INVALID_PARAMETER_MIX;
 	}
 
-	no_sign_flags = SMB2_SESSION_FLAG_IS_GUEST | SMB2_SESSION_FLAG_IS_NULL;
+	if (!conn->mandatory_signing) {
+		/*
+		 * only allow guest sessions without
+		 * mandatory signing.
+		 *
+		 * If we try an authentication with username != ""
+		 * and the server let us in without verifying the
+		 * password we don't have a negotiated session key
+		 * for signing.
+		 */
+		no_sign_flags = SMB2_SESSION_FLAG_IS_GUEST;
+	}
 
 	if (session->smb2->session_flags & no_sign_flags) {
 		session->smb2->should_sign = false;