Drop too-short control channel packets instead of asserting out.

syzzer · cron2 · commit c5590a6821e3 · 2014-11-28T20:28:53.000+01:00
This fixes a denial-of-service vulnerability where an authenticated client could stop the server by triggering a server-side ASSERT(). OpenVPN would previously ASSERT() that control channel packets have a payload of at least 4 bytes. An authenticated client could trigger this assert by sending a too-short control channel packet to the server. Thanks to Dragana Damjanovic for reporting the issue. This bug has been assigned CVE-2014-8104. Signed-off-by: Steffan Karger <steffan.karger@fox-it.com> Acked-by: Gert Doering <gert@greenie.muc.de> Message-Id: <1CED409804E2164C8104F9E623B08B9018803B0FE7@FOXDFT02.FOX.local> Signed-off-by: Gert Doering <gert@greenie.muc.de>
diff --git a/src/openvpn/ssl.c b/src/openvpn/ssl.c
@@ -2036,7 +2036,11 @@ key_method_2_read (struct buffer *buf, struct tls_multi *multi, struct tls_sessi
   ASSERT (session->opt->key_method == 2);
 
   /* discard leading uint32 */
-  ASSERT (buf_advance (buf, 4));
+  if (!buf_advance (buf, 4)) {
+    msg (D_TLS_ERRORS, "TLS ERROR: Plaintext buffer too short (%d bytes).",
+	buf->len);
+    goto error;
+  }
 
   /* get key method */
   key_method_flags = buf_read_u8 (buf);
