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TUCoPS :: Linux :: General :: bt51.txt

Options Parsing Tool library buffer overflows.




 
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Secure Network Operations, Inc.           http://www.secnetops.com
Strategic Reconnaissance Team	            research@secnetops.com
Team Lead Contact		                  kf@secnetops.com


Our Mission:
************************************************************************
Secure Network Operations offers expertise in Networking, Intrusion 
Detection Systems (IDS), Software Security Validation, and 
Corporate/Private Network Security. Our mission is to facilitate a 
secure and reliable Internet and inter-enterprise communications 
infrastructure through the products and services we offer. 


Quick Summary:
************************************************************************
Advisory Number		: SRT2003-04-24-1532.txt
Product			: Options Parsing Tool shared library
Version			: <= opt-3.18
Vendor			: http://nis-www.lanl.gov/~jt/
Class			: local
Criticality             : Low 
Operating System(s)	: Linux (other unix based?)


High Level Explanation
************************************************************************
High Level Description	: Error messages can cause buffer overflow 
What to do		: recompile and link against newest libopt.a

Technical Details
************************************************************************
Proof Of Concept Status : No PoC needed for this issue. 
Low Level Description	: 

The Options Parsing Tool shared library is a subroutine library which 
facilitates the convenient input of parameters to a C or C++ program.
The package attempts to provide a direct and relatively full-featured 
input interface to the end user of the program, and at the same time 
impose a minimal amount of work on the programmer to "attach" the package 
to his or her software.

I am not aware of any suid programs linking against this library but 
at the very least Debian provides it as a .deb package. Obvious issues 
are raised if a suid application makes use of the OPT libraries. 
http://packages.debian.org/stable/devel/opt.html

The error messages in opt pass through one of several functions in order
to print the error to the screen. Either opt_warn_1(), opt_warn_2(), 
opt_warn_3(), opt_fatal_1(), opt_fatal_2(), or opt_fatal_3() will be 
used when an error occurs. Several similar functions could cause issues
with buffer overflows. 

This simple test will show the problems associated with using <= opt-3.18

[dotslash@vegeta test]$ cat > test.c
main(int *argc, char **argv)
{
	/* use lubc atoi() */
        int x = atoi(argv[1]);
        printf("atoi(): %i\n", x);

	/* use OPT opt_atoi() */
        int y = opt_atoi(argv[2]);
        printf("opt_atoi(): %i\n", y);
}

[dotslash@vegeta test]$ cc -o test test.c ../src/libopt.a
[dotslash@vegeta test]$ ./test 1 2
atoi(): 1
opt_atoi(): 2

[dotslash@vegeta test]$ ./test `perl -e 'print "A" x 986'` B
atoi(): 0
OPT Warning: String [B] is not a valid integer, will use [0]
opt_atoi(): 0

[dotslash@vegeta test]$ ./test A `perl -e 'print "A" x 986'`
atoi(): 0
OPT Warning: String
[AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA...
is not a valid integer, will use [0]
opt_atoi(): 0
Segmentation fault

strace tells us that we are able to overwrite the eip. 
[41414141] --- SIGSEGV (Segmentation fault) @ 0 (0) ---

This occurs because of the following code is triggered when reading
input from the user. 

long
opt_atoi(char *s)
{
  int valid;
  long x;
  x = (long)atof(s); /* Call atof() whether or not string is valid,
                      * because some strings, eg '15x' can still be
                      * interpreted as numeric.  But give a warning
                      * unless the string really is valid
                      */

  valid = opt_isvalidnumber(s);
  if (!valid || (valid & OPT_NUM_FLOAT)) {
    opt_warn_2("String [%s] is not a valid integer, will use [%ld]",s,x);
  }
  return x;
}

This particular segfault was caused by the opt_warn_2 definition in opt_p.h. 
You can see that the data passed on by the user is used in a sprintf() into 
a static sized buffer. 

#define OPT_ERRMAXSTRLEN 1024  /* shouldn't be fixed length, but it is! */
...
#define opt_warn_2(fmt,var1,var2) do { \
    char gstr[OPT_ERRMAXSTRLEN]; sprintf(gstr,fmt,var1,var2); \
        opt_warning(gstr); } while(0)

A diff with the new version shows the implementation of snprintf as a valid fix. 

<     char gstr[OPT_ERRMAXSTRLEN]; sprintf(gstr,fmt,var1,var2,var3); \
---
>     char gstr[OPT_ERRMAXSTRLEN]; \
>         opt_snprintf_3(gstr,OPT_ERRMAXSTRLEN,fmt,var1,var2,var3); \

A quick test compile against the new version of libopt.a appears to take care 
of the problem.

[dotslash@vegeta test]$ pwd
/home/dotslash/opt/opt-3.19/test
[dotslash@vegeta test]$ cc -o test test.c ../src/libopt.a

[dotslash@vegeta test]$ ltrace ./test A `perl -e 'print "A" x 1986'`
...
snprintf("String [AAAAAAAAAAAAAAAAAAAAAAAA"..., 1024, "String [%s] is not a valid integ"...

Patch or Workaround	: Relink applications that use libopt.a against the 
new version of opt at http://nis-www.lanl.gov/~jt/Software/opt/opt-3.19.tar.gz

Vendor Status		: Author has responded and applied a fix to the problem.

Bugtraq URL		: to be assigned

------------------------------------------------------------------------
This advisory was released by Secure Network Operations,Inc. as a matter
of notification to help administrators protect their networks against
the described vulnerability. Exploit source code is no longer released
in our advisories. Contact research@secnetops.com for information on how
to obtain exploit information.


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