[UNIX] Options Parsing Tool Shared Library Vulnerability

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Date: 04/28/03

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Date: 28 Apr 2003 11:19:40 +0200

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      Options Parsing Tool Shared Library Vulnerability
    ------------------------------------------------------------------------

    SUMMARY

     <http://nis-www.lanl.gov/~jt/Software/> OPT is "a subroutine library
    which facilitates the convenient input of parameters to a C or C++
    program". An error message displayed by the program contains an
    exploitable buffer overflow allowing local attackers to execute arbitrary
    code.

    DETAILS

    Vulnerable systems:
     * OPT version 3.18 and prior

    Immune systems:
     * OPT version 3.19

    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:
Re-link 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> 
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.
ADDITIONAL INFORMATION
The information has been provided by  <mailto:research@secnetops.com> 
Strategic Reconnaissance Team.
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