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Fix remotely-triggerable ASSERT() on malformed IPv6 packet.

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Correct sanity checks on IPv6 packet length in mss_fixup_ipv6(),
and change the ASSERT() check in mss_fixup_dowork() into a simple
"return" (= the TCP header will simply not be inspected further).

CVE-2017-7508 has been assigned due to the serious nature of the
bug: it can be used to remotely shutdown an openvpn server or
client, if IPv6 and --mssfix are enabled and the IPv6 networks used
inside the VPN are known.

Found by Guido Vranken <guidovranken@gmail.com>.

v2: style changes

CVE: 2017-7508
Signed-off-by: Gert Doering <gert@greenie.muc.de>
Acked-by: Steffan Karger <steffan.karger@fox-it.com>
Message-Id: <20170613200832.15027-1-gert@greenie.muc.de>
URL: https://www.mail-archive.com/search?l=mid&q=20170613200832.15027-1-gert@greenie.muc.de
Signed-off-by: Gert Doering <gert@greenie.muc.de>
(cherry picked from commit c3f47077a7756de5929094569421a95aa66f2022)
This commit is contained in:
Gert Doering 2017-06-13 22:08:32 +02:00
parent f38a4a1059
commit fc61d1bda1
No known key found for this signature in database
GPG Key ID: 1D829EFECA562812
1 changed files with 9 additions and 2 deletions
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11
src/openvpn/mss.c
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@ -110,8 +110,12 @@ mss_fixup_ipv6 (struct buffer *buf, int maxmss)
if ( pip6->nexthdr != OPENVPN_IPPROTO_TCP )
return;
/* skip IPv6 header (40 bytes),
* verify remainder is large enough to contain a full TCP header
*/
newbuf = *buf;
if ( buf_advance( &newbuf, 40 ) )
if (buf_advance( &newbuf, 40 )
&& BLEN(&newbuf) >= (int) sizeof(struct openvpn_tcphdr))
{
struct openvpn_tcphdr *tc = (struct openvpn_tcphdr *) BPTR (&newbuf);
if (tc->flags & OPENVPN_TCPH_SYN_MASK)
@ -133,7 +137,10 @@ mss_fixup_dowork (struct buffer *buf, uint16_t maxmss)
int accumulate;
struct openvpn_tcphdr *tc;
ASSERT (BLEN (buf) >= (int) sizeof (struct openvpn_tcphdr));
if (BLEN(buf) < (int) sizeof(struct openvpn_tcphdr))
{
return;
}
verify_align_4 (buf);
tc = (struct openvpn_tcphdr *) BPTR (buf);