[waraxe-2010-SA#077] - Multiple Vulnerabilities in Calibre 0.7.34 =============================================================================== Author: Janek Vind "waraxe" Date: 20. December 2010 Location: Estonia, Tartu Web: http://www.waraxe.us/advisory-77.html Affected Software: ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Calibre is a free and open source e-book library management application developed by users of e-books for users of e-books. It has a cornucopia of features divided into the following main categories: Library Management, E-book conversion, Syncing to e-book reader devices, Downloading news from the web and converting it into e-book form, Comprehensive e-book viewer, Content server for online access to your book collection http://calibre-ebook.com/ Affected versions ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Tests were conducted against Calibre version 0.7.34 for Windows, older versions may be vulnerable as well. Other platform versions were not tested. ############################################################################### 1. Directory Traversal Vulnerability in Calibre Content Server ############################################################################### Reason: failure to sufficiently sanitize user-supplied input data Attack vector: specially crafted HTTP GET request Preconditions: 1. Calibre Content Server must be turned on (off by default) 2. If Username and Password set, they must be known (no password by default) Impact: remote attacker can read arbitrary files on the target system So, I was interested in e-book management software and after some research found Calibre. It has useful feature - Content Server. Basically it's Webserver, based on CherryPy, written in Python. As specialized in Web Application Security, then obviously I spent some time playing with it. I used Firefox with Live HTTP Headers Add-On, which provides easy way to observe HTTP requests and responses. This is what got my attention: http://localhost:8080/static/browse/browse.css http://localhost:8080/static/jquery_ui/css/humanity-custom/jquery-ui-1.8.5.custom.css http://localhost:8080/static/jquery.multiselect.css Seems like accessing static resources. Norhing unusual. But what if ... http://localhost:8080/static/browse/waraxe Oops, something crashed: ------------------------------------------------------------------------------- 500 Internal Server Error The server encountered an unexpected condition which prevented it from fulfilling the request. Traceback (most recent call last): File "site-packages\cherrypy\_cprequest.py", line 606, in respond File "site-packages\cherrypy\_cpdispatch.py", line 25, in __call__ File "site-packages\calibre\library\server\utils.py", line 51, in do File "site-packages\calibre\library\server\content.py", line 98, in static KeyError: u'browse/waraxe' Powered by CherryPy 3.1.2 ------------------------------------------------------------------------------- So we can see, that static resources are handled via "content.py". Calibre is Open Source software, so no need for reverse engineering. Source code snippet: ------------------------------------------------------------------------------- def static(self, name): 'Serves static content' name = name.lower() cherrypy.response.headers['Content-Type'] = { 'js' : 'text/javascript', 'css' : 'text/css', 'png' : 'image/png', 'gif' : 'image/gif', 'html' : 'text/html', '' : 'application/octet-stream', }[name.rpartition('.')[-1].lower()] cherrypy.response.headers['Last-Modified'] = self.last_modified(self.build_time) ------------------------------------------------------------------------------- As seen above, no checks for dot-dot-slash (../), so Directory Traversal vulnerability may exist. Quick look at Calibre install directory revealed the fact, that static resources folder is located here: C:\Program Files (x86)\Calibre2\resources\content_server\ Let's see, if we can fetch files outside of that directory: http://localhost:8080/static/../jquery.simulate.js I was testing it with Firefox 3.6.13 and Live HTTP Headers revealed problem: GET /jquery.simulate.js HTTP/1.1 It appears, that modern web browsers (FF, IE, Opera at least) will not let directory traversal tests via GET request. Fine, let's then use php: ------------------------------------------------------------------------------- ------------------------------------------------------------------------------- YES, it worked, we were able to read js file outside the predetermined directory. Now let's try file reading from Windows directory: ------------------------------------------------------------------------------- ------------------------------------------------------------------------------- And we get unexpected crash :( ------------------------------------------------------------------------------- 500 Internal Server Error The server encountered an unexpected condition which prevented it from fulfilling the request. Traceback (most recent call last): File "site-packages\cherrypy\_cprequest.py", line 606, in respond File "site-packages\cherrypy\_cpdispatch.py", line 25, in __call__ File "site-packages\calibre\library\server\utils.py", line 51, in do File "site-packages\calibre\library\server\content.py", line 98, in static KeyError: u'ini' ------------------------------------------------------------------------------- As seen above, files with extension "js", "css", "png", "gif" and "html" as well as files without extension (filename ends with dot) are retrievable, but in case of "wrong" extension vulnerable python script will crash because of missing entry in extensions array (formal definition: exception KeyError - Raised when a mapping (dictionary) key is not found in the set of existing keys). At first this seemed as minor security issue - only js, css, png, gif, html and extensionless files from remote system can be retrieved. But after playing around some time I found useful artifact - concatenation of space or dot character to the end of the filename will pass through the python script without crashing it and we can read arbitrary files from remote system. Now this is major security issue here! Below is test script for proof of concept: ------------------------------------------------------------------------------- ------------------------------------------------------------------------------- By the way, that trick with trailing dot or space character(s) is based on Win32 API features. I tried it in php and python, in both cases we can open same file with paths "waraxe.txt", "waraxe.txt.", "waraxe.txt ", "waraxe.txt. . .". I tried Win32 API CreateFile() from C code and it worked in same way. Seems like useful trick :) ############################################################################### 2. Reflected XSS Vulnerability in Calibre Content Server ############################################################################### Reason: failure to sufficiently sanitize user-supplied input data Attack vector: user-supplied GET parameter "query" Preconditions: 1. Calibre Content Server must be turned on (off by default) 2. If Username and Password set, they must be known (no password by default) Example attack: http://127.0.0.1:8080/browse/search?query= Disclosure Timeline: ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 20.12.2010 Developer contacted via email 20.12.2010 Developer gave green light for going public 20.12.2010 Public disclosure Greetings: ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Greets to ToXiC, y3dips, Sm0ke, Heintz, slimjim100, pexli, zerobytes, vince213333, to all active waraxe.us forum members and to anyone else who know me! Contact: ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ come2waraxe@yahoo.com Janek Vind "waraxe" Waraxe forum: http://www.waraxe.us/forums.html Personal homepage: http://www.janekvind.com/ Random project: http://errorhelpdesk.com/ ---------------------------------- [ EOF ] ------------------------------------