Fix bounds check in read_key()

The bounds check in read_key() was performed after using the value, instead
of before.  If 'key-method 1' is used, this allowed an attacker to send a
malformed packet to trigger a stack buffer overflow.

Fix this by moving the input validation to before the writes.

Note that 'key-method 1' has been replaced by 'key method 2' as the default
in OpenVPN 2.0 (released on 2005-04-17), and explicitly deprecated in 2.4
and marked for removal in 2.5.  This should limit the amount of users
impacted by this issue.

CVE: 2017-12166
Signed-off-by: Steffan Karger <steffan.karger@fox-it.com>
Acked-by: Gert Doering <gert@greenie.muc.de>
Acked-by: David Sommerseth <davids@openvpn.net>
Message-Id: <80690690-67ac-3320-1891-9fecedc6a1fa@fox-it.com>
URL: https://www.mail-archive.com/search?l=mid&q=80690690-67ac-3320-1891-9fecedc6a1fa@fox-it.com
Signed-off-by: David Sommerseth <davids@openvpn.net>
(cherry picked from commit 3b1a61e9fb27213c46f76312f4065816bee8ed01)

diff --git a/src/openvpn/crypto.c b/src/openvpn/crypto.c
index 33d6fe1ad1c10a05173114a695c5e14bb579ceb4..03e880e279b27a313b70340a7e88fadf33c08c24 100644 (file)
--- a/src/openvpn/crypto.c
+++ b/src/openvpn/crypto.c
@@ -1689,6 +1689,11 @@ read_key(struct key *key, const struct key_type *kt, struct buffer *buf)
         goto read_err;
     }
 
+    if (cipher_length != kt->cipher_length || hmac_length != kt->hmac_length)
+    {
+        goto key_len_err;
+    }
+
     if (!buf_read(buf, key->cipher, cipher_length))
     {
         goto read_err;
@@ -1698,11 +1703,6 @@ read_key(struct key *key, const struct key_type *kt, struct buffer *buf)
         goto read_err;
     }
 
-    if (cipher_length != kt->cipher_length || hmac_length != kt->hmac_length)
-    {
-        goto key_len_err;
-    }
-
     return 1;
 
 read_err: