7. Scanners

 

Enough research will tend to support your theory.

 Murphy's Law of Research

This is the platform dependent part of Scanners (i). It contains three things:

All together this results in a kind of time warp. The infection methods detected here are described later on.

7.1. Finding executables

First a sample from file to show how the sed part is supposed to work.

And now the output of find_exec.sh for both the big and the small set of target executables. Linux distributions and Solaris have very few statically linked programs. On FreeBSD the number is much higher.

7.2. Scan entry point

See Sections for the illustrative description of a dumped ELF header.

Output: out/i386-redhat7.3-linux/scanner/entry_point/big.static
files=0012; detected=0000

Output: out/i386-redhat7.3-linux/scanner/entry_point/big.dynamic
files=1147; detected=0000

Well, on a clean system there are absolutely no deviations. Now we let the script loose on all infected executables produced from the sources of this document. Only a few are detected (note the directory name e1i1). Which means there is cure against this vulnerability (see The entry point). In the following output ep means "entry point" and sot is "start of .text".

Output: out/i386-redhat7.3-linux/scanner/entry_point/small.dynamic
segment_padding/e1i1/tcsh_infected           ep=0x808af70  sot=0x804a1f0 
segment_padding/e1i1/perl_infected           ep=0x80f2260  sot=0x8059b20 
segment_padding/e1i1/mt_infected             ep=0x804a590  sot=0x8048690 
segment_padding/e1i1/bash_infected           ep=0x80c6420  sot=0x8059440 
segment_padding/e1i1/strip_bash_infected     ep=0x80c6420  sot=0x8059440 
files=0035; detected=0005

7.3. Scan segments

Note that only the last few lines of output are shown.

On this installation at least 500 + 7 files are possible targets for Segment padding infection. So on to all infected executables created from the sources of this document. Again only the last few lines of output is shown. It's enough to see that all infected files are detected.

Output: out/i386-redhat7.3-linux/scanner/segment/small.dynamic
CHECK: 12 > 4096; 0xc > 0x1000
CHECK: tmp/i386-redhat7.3-linux/doing_it_in_c/e3i4/strip_bash_infected
CHECK: src/scanner/segment/action.inc#17
CHECK: (delta) > (0x1000)
CHECK: 12 > 4096; 0xc > 0x1000
CHECK: tmp/i386-redhat7.3-linux/doing_it_in_c/e3i4/strip_bash_infected
CHECK: src/scanner/segment/action.inc#20
CHECK: (delta) > (0x1000)
CHECK: 12 > 4096; 0xc > 0x1000
files=35; ok=0; det_page=35; det_align=30; min=0x000c; max=0x001e

7.4. A shell for segment padding

I want to demonstrate infection methods on a shell. The usual suspect is /bin/sh. But on some systems that particular executable is not vulnerable to Segment padding infection.

Source: pre/i386-redhat7.3-linux/scanner/find-shell.sh
#!/bin/bash
/bin/sed -ne 's/ \.\.\. .* Ok$//p' \
	out/i386-redhat7.3-linux/scanner/segment/big.dynamic.full \
	out/i386-redhat7.3-linux/scanner/segment/big.static.full \
| /bin/grep -f ./src/scanner/find-shell.lst
/bin/echo status=$?

Source: src/scanner/find-shell.lst
bin/ash\>
bin/bash\>
bin/bsh\>
bin/csh\>
bin/ksh\>
bin/sash\>
bin/sh\>
bin/tcsh\>

Output: out/i386-redhat7.3-linux/scanner/find-shell
/bin/bash
/bin/ash
/bin/tcsh
/bin/ash.static
status=0

7.5. Scan file size