VULNERABLE SOFTWARE VERSIONS TWiki http://twiki.org/ - TWiki 20030201 (e.g. Debian Sarge) - probably later versions - Subversion repository at at least until revision 3224 (including) ATTACK VECTORS HTTP GET requests towards the Wiki server (typically port 80/TCP). Usually, no prior authentication is necessary. Possibly also HTTP POST, but this is untested. IMPACT An attacker is able to execute arbitrary shell commands with the privileges of the TWiki process. DETAILS The TWiki search function uses a user supplied search string to compose a command line executed by the Perl backtick (``) operator. The search string is not checked properly for shell metacharacters and is thus vulnerable to search string containing quotes and shell commands. An example search string would be: doesnotexist1'; (uname -a; id) | sed 's/\(.*\)/__BEGIN__\1__END__.txt/'; fgrep -i -l -- 'doesnotexist2 If access to the Wiki is not restricted by other means, attackers can use the search function without prior authentication. As indicated in the source code, the software authors were aware that the way they worked around Perl's taint check is insecure. Users of TWiki should reconsider if the software can meet their security requirements, given such gross negligence. COUNTERMEASURES - Hotfix (see patch at end of advisory) The hotfix is known to prevent the current attacks, but it might not be a complete fix. - Filter access to the web server. - Use the web server software to restrict access to the web pages served by TWiki. - Rewrite the TWiki code to correctly check user supplied strings. - Rewrite the TWiki code to use Perl code to open and scan the files instead of running commands in the shell. AUTHORS AND CREDITS Markus Goetz, Joerg Hoh, Michael Holzt, Florian Laws, Hans Ulrich Niedermann, Andreas Thienemann, Peter Thoeny, Florian Weimer contributed to this advisory. HOTFIX --- twiki/lib/TWiki/Search.pm.orig 2004-11-12 20:16:56.000000000 +0100 +++ twiki/lib/TWiki/Search.pm 2004-11-12 20:36:21.000000000 +0100 @@ -135,6 +135,11 @@ my $tempVal = ""; my $tmpl = ""; my $topicCount = 0; # JohnTalintyre + + # Hotfix for search string shell code insertion vulnerability + $theSearchVal =~ s/[^A-Za-z0-9+\-_]//g; # only accept known-good chars + $theSearchVal = substr($theSearchVal, 0, 100); # limit string to reasonable length + my $originalSearch = $theSearchVal; my $renameTopic; my $renameWeb = ""; VULNERABILITY TIMELINE early October 2004 earliest confirmed attack 2004-11-12 forensics revealed exploit vendor contact vendor responded, with less conservative hotfix 2004-11-13 uncoordinated emergency disclosure _______________________________________________ Full-Disclosure - We believe in it. Charter: http://lists.netsys.com/full-disclosure-charter.html