Apple OS X Sandbox Predefined Profiles Bypass
1. Advisory Information
Title: Apple OS X Sandbox Predefined Profiles Bypass
Advisory ID: CORE-2011-0919
Advisory URL: http://www.coresecurity.com/content/apple-osx-sandbox-bypass
Date published: 2011-11-10
Date of last update: 2011-11-10
Vendors contacted: Apple
Release mode: User release
2. Vulnerability Information
3. Vulnerability Description
Several of the default pre-defined sandbox profiles don't properly limit all the available mechanisms and therefore allow exercising part of the restricted functionality. Namely, sending Apple events is possible within the no-network sandbox (kSBXProfileNoNetwork). A compromised application hypothetically restricted by the use of the no-network profile may have access to network resources through the use of Apple events to invoke the execution of other applications not directly restricted by the sandbox.
It is worth mentioning that a similar issue was reported by Charlie Miller in his talk at Black Hat Japan 2008 . He mentioned a few processes sandboxed by default as well as a method to circumvent the protection. Sometime after the talk, Apple modified the mentioned profiles by restricting the use of Apple events but did not modify the generic profiles.
4. Vulnerable packages
- Apple Mac OS X 10.7.x
- Apple Mac OS X 10.6.x
- Apple Mac OS X 10.5.x
5. Non-vulnerable packages
- Apple Mac OS X 10.4
6. Vendor Information, Solutions and Workarounds
Contact the vendor for more information.
8. Technical Description / Proof of Concept Code
The use of Apple events is possible within the several default profiles as no-network, no-internet (kSBXProfileNoNetwork, kSBXProfileNoInternet) and others. A compromised application hypothetically restricted by the use of the no-network profile may have access to network resources through the use of Apple events to invoke the execution of other applications not directly restricted by the sandbox.
As Apple's "App Sandbox Design Guide" document points out, applications that require sending Apple events to other arbitrary applications are not suitable for sandboxing, because some developer tools restrict Apple events by default while defining the sandbox. The reason for this is that, as we show here, by dispatching Apple events a process can escape the sandbox .
The method used by Charlie Miller involves dropping a script to the disk and getting it executed by launchd via launchctl. Our approach is technically the same without the need to drop a file. In our PoC we used "osascript" to send the required Apple events to launchd in order to execute the new process. As the new process is not a 'child' of the sandboxed process, it is created without the sandbox restrictions.
An additional risk with these profiles is that they are supposed to provide an example of how a process should be restricted in different scenarios. If the no-network profile allows Apple-script events, this may result in new applications using the same restriction rules, therefore offering a false sense of security.
The following PoC illustrates this vulnerability:
import os import sys import socket if len(sys.argv) != 2: print "[-] Usage: sandbox-exec -n no-network python %s hostname" % sys.argv try: targetIP = sys.argv s = socket.socket() s.connect((targetIP, 80)) s.send('GET /\r\n\r\n') print(s.recv(1024)) print "\n\n\n[+] Sandbox escaped" except Exception, e: if "Operation not permitted" in str(e): #print repr(e) print "[-] Blocked by seatbelt" print "[ ] Escaping..." os.system("""/usr/bin/osascript -e 'tell application "Terminal" to do script "python %s %s"'""" % (sys.argv, targetIP))
9. Report Timeline
- 2011-09-20: Core Security Technologies notifies Apple Product Security of the vulnerability, including technical details. Preliminary publication date is set to November 7, 2011.
- 2010-09-20: Vendor acknowledges the receipt of the information.
- 2010-10-05: Vendor informs that it does not see any actual security implications. The kSBXProfileNoNetwork sandbox profile does not promise that Apple Events will be blocked in the documentation. (Specifically, all it guarantees is "all sockets-based networking is prohibited".)
- 2011-10-13: Core responds that the kSBXProfileNoNetwork sandbox profile should guarantee that "all sockets-based networking is prohibited". The PoC sent to Apple shows that through the use of Apple events (osascript is used in the PoC just to keep it simple) an attacker could circumvent the restriction. So, at the end, sockets-based networking is used.
- 2010-10-18: Vendor responds that it is currently considering modifying its documentation to explicitly point out what Core described; namely, that the restrictions that these particular sandbox profiles provide are limited to the process in which the sandbox is applied.
- 2011-11-10: The advisory CORE-2011-0919 is published as user release.
 App Sandbox Design Guide -- Designing for App Sandbox
 Charlie Miller, "Hacking OS X", Black Hat Japan 2008
11. About CoreLabs
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12. About Core Security Technologies
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The contents of this advisory are copyright (c) 2011 Core Security Technologies and (c) 2011 CoreLabs, and are licensed under a Creative Commons Attribution Non-Commercial Share-Alike 3.0 (United States) License: http://creativecommons.org/licenses/by-nc-sa/3.0/us/
14. PGP/GPG Keys
This advisory has been signed with the GPG key of Core Security Technologies advisories team, which is available for download at /legacy/files/attachments/core_security_advisories.asc.