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phpBB Attachment Mod Directory Traversal HTTP POST Injection
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SUMMARY
<http://www.phpBB.org> phpBB is "a high powered, fully scalable, and
highly customizable open-source bulletin board package. phpBB has a
user-friendly interface, simple and straightforward administration panel,
and helpful FAQ. Based on the powerful PHP server language and your choice
of MySQL, MS-SQL, PostgreSQL or Access/ODBC database servers, phpBB is the
ideal free community solution for all web sites."
An HTTP POST Injection vulnerability exists in the <http://opentools.de>
Attachment Mod written by Meik Sievertsen AKA Acyd Burn that enables
anyone to traverse directories on the web server.
DETAILS
Vulnerable Systems:
* phpBB's Attachment Module version 2.3.10 and prior
Immune Systems:
* phpBB's Attachment Module version 2.3.11 or newer
Due to insufficient sanitizing of the filename in the attachment mod user
interface, a user can inject a filename via HTTP POST that includes a
directory traversal vulnerability: "../../". This injection can be done
via the "physical_filename" and/or "real_filename" fields.
Once the database table has a directory traversal filename stored in it,
for example: "../../$newfilename", you can use the download.php file to
obtain files stored outside the UPLOAD_DIR location.
Impact:
With this an attacker could be able to add/remove/execute files outside of
the UPLOAD_DIR directory.
Proof Of Concept:
1) Visit a website that has attachmod installed under phpBB
2) Start a new topic, attach a file via the "Add Attachment" input button
3) Prior to clicking "Submit", view the page source via your browser's
"View Source"
4) Modify the <FORM> entry if required to send the POST back to the
website
5) Modify the two values for the input names "attachment_list[]" and
"filename_list[]" from "$oldfilename" to "../../$newfilename"
6) Save the page, load it in your browser, and click "Submit"
An un-patched attachmod site will now have "../../$newfilename" in:
$prefix_attachments_desc.physical_filename
$prefix_attachments_desc.real_filename
And when a user accesses the file via the attachmod's download.php
generated link, instead of serving "$filename" from the UPLOAD_DIR
location, it will serve the user the "../../$newfilename" if it exists.
Disclosure Timeline:
Dec 7 2004: Exploit discovered during an audit
Dec 8 2004: Author was contacted with this advisory
Dec 9 2004: Author developed a patch. Basic static test of the patch
shows success in stopping the exploit
Dec 12 2004: Author released version 2.3.11 to the public
Dec 14 2004: Advisory released to the public
ADDITIONAL INFORMATION
The information has been provided by <mailto:zx@castlecops.com> Paul
Laudanski.
The original article can be found at:
<http://castlecops.com/postp393483.html>
http://castlecops.com/postp393483.html
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