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

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>
(cherry picked from commit c5590a6821e37f3b29735f55eb0c2b9c0924138c)

Steffan Karger authored on 2014/11/20 21:43:05
Showing 1 changed files

src/openvpn/ssl.c

History View file @ 97597e7

@@ -2035,7 +2035,11 @@ 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);