Prevent two kinds of stack buffer OOB reads and a crash for invalid input data

Pre-authentication remote crash/information disclosure for clients

If clients use a HTTP proxy with NTLM authentication (i.e.
"--http-proxy <server> <port> [<authfile>|'auto'|'auto-nct'] ntlm2"),
a man-in-the-middle attacker between the client and the proxy can
cause the client to crash or disclose at most 96 bytes of stack
memory. The disclosed stack memory is likely to contain the proxy
password.

If the proxy password is not reused, this is unlikely to compromise
the security of the OpenVPN tunnel itself.  Clients who do not use
the --http-proxy option with ntlm2 authentication are not affected.

CVE: 2017-7520
Signed-off-by: Guido Vranken <guidovranken@gmail.com>
Acked-by: Gert Doering <gert@greenie.muc.de>
Message-Id: <CAO5O-EJvHKid-zTj+hmFG_3Gv78ixqCayE9=C62DZaxN32WNtQ@mail.gmail.com>
URL: https://www.mail-archive.com/search?l=mid&q=CAO5O-EJvHKid-zTj+hmFG_3Gv78ixqCayE9=C62DZaxN32WNtQ@mail.gmail.com
Signed-off-by: Gert Doering <gert@greenie.muc.de>
(cherry picked from commit 7718c8984f04b507c1885f363970e2124e3c6c77)

diff --git a/src/openvpn/ntlm.c b/src/openvpn/ntlm.c
index 16d60d2cdd078dddb50dc3717bc57bdcc4581ba0..0b1163ee4658b55b51a6ad40cb1c25e57ec449dc 100644 (file)
--- a/src/openvpn/ntlm.c
+++ b/src/openvpn/ntlm.c
@@ -195,7 +195,7 @@ ntlm_phase_3(const struct http_proxy_info *p, const char *phase_2, struct gc_are
      */
 
     char pwbuf[sizeof(p->up.password) * 2]; /* for unicode password */
-    char buf2[128]; /* decoded reply from proxy */
+    unsigned char buf2[128]; /* decoded reply from proxy */
     unsigned char phase3[464];
 
     char md4_hash[MD4_DIGEST_LENGTH+5];
@@ -301,7 +301,13 @@ ntlm_phase_3(const struct http_proxy_info *p, const char *phase_2, struct gc_are
                 tib_len = 96;
             }
             {
-                char *tib_ptr = buf2 + buf2[0x2c];           /* Get Target Information block pointer */
+                char *tib_ptr;
+                int tib_pos = buf2[0x2c];
+                if (tib_pos + tib_len > sizeof(buf2))
+                {
+                    return NULL;
+                }
+                tib_ptr = buf2 + tib_pos;                               /* Get Target Information block pointer */
                 memcpy(&ntlmv2_blob[0x1c], tib_ptr, tib_len);           /* Copy Target Information block into the blob */
             }
         }