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Lockdown Playground

Lockdown related research, tools and POCs. All POCs should work fine on iOS 12.2 and below.

It was a fun research project and I hope you enjoy the short writeup.

Note that I omitted some details about existing underlaying issues.

FAQ

  • Is this a jailbreak? NO
  • Will this be used in a jailbreak? Maybe, but probably not
  • Will this lead to other useful tools and discoveries? Maybe

For any other questions you may contact me at:

  • @DanyL931 - Twitter
  • @DanyL - GitHub

Compiling

The project was developed and tested under macOS Mojave, but should work fine on older macOS versions as well. Other than the iOS app, the code should be quite easy to port and support other operating systems.

Dependencies:

  • libimobiledevice (HEAD)
  • libplist (HEAD)
  • libzip (for system_app_man)
  • libcurl (for system_app_man)

macOS:

  • Set a valid signing identity for the launchdown_helper target.
  • Make sure LDFLAGS are configured correctly.
  • Build All scheme using Xcode, or just run:

xcodebuild -scheme All -project lockdownd_playground.xcodeproj build

  • Compiled binaries will result in build/release or build/debug, depending on the build type used.

launchdown

Exploits CVE-2019-8637 to achieve a launchd job submission primitive and implements a shell-like CLI interface on top of it.

This can be used for research purposes, altering system state and triggering additional vulnerabilities.

Usage: 	launchdown [OPTIONS] COMMAND
	launchdown [-v] [-u] [--user <USER>] [-l] exec <PROGRAM> [ARG1, ...]
	launchdown [-v] [-u] [-l] xpc <XPC_SERVICE_NAME>
	launchdown [-v] [-u] [-l] raw <SERVICE_PLIST>
	launchdown [-v] [-u] [--user <USER>] [-l] test

Options:
	--user	- Specifies the user to run the job as. (defaults to 'root' unless command 'test' is used)
	--label - Specifies a unique job identifier to lockdownd.
 	-v	- Set verbosity level (Incremental)
	-u	- Target specific device by UDID
 	-h	- Prints usage information

Commands:
 	exec <command>	Executes the given command
 	xpc  <label>	Spawn the given XPC Service. (Only services reachable to lockdownd)
 	test		Executes launchdown-helper in test mode which prints username, uid and gid to syslog.
			* Sets user to '_networkd'.
			  Because of sandbox restrictions containermanagerd is unable to
			  create containers for users other than 'mobile' and '_networkd'.
			  (Use '--user' option to override)

		-------------------------------------------------------------------
		-- Make sure launchdown-helper app is compiled & properly signed --
		-------------------------------------------------------------------

MobileStorageMounter strikes again! or was it?

After mounting a DeveloperDiskImage and loading new Launch Daemons, MobileStorageMounter will use the distributed notification center to inform other system services about the new disk image mount and it will send its type and mount point inside a user info dictionary.

A little help from grep -r revealed that the observers of this notification are installd and lockdownd, which will load new applications and lockdown agents (respectively) upon a relative path to the mount point sent by MobileStorageMounter.

By spoofing the above notification from a 3rd party application, I was able to control the path from which installd and lockdownd are loading their resources. While installd complained about insufficient permissions, I was able to fool lockdownd into loading and launching my own agents from /var/mobile/Media/Library/Lockdown/ServiceAgents.

Note that the vulnerability in installd is still present on iOS 12.3

CVE-2019-8637 (MobileLockdown):

Available for: iPhone 5s and later, iPad Air and later, and iPod touch 6th generation
Impact: A malicious application may be able to gain root privileges
Description: An input validation issue was addressed with improved input validation.
CVE-2019-8637: Dany Lisiansky (@DanyL931)

New Mitigations:

  • lockdownd now verifies the mount point path against a list of mount points retrieved by using the MobileStorageCopyDevices API.

patchy

Exploits some of the mitigations patched by CVE-2019-8593 and the MobileInstallation bugs described below to form a TOCTTOU attack against AppleFileConduit and MobileInstallation to allow modification of protected application bundles right after installation, and therefore bypassing package inspection.

This may be used to corrupt applications and other installable bundles (like removable system apps, Swift Playgrounds, Carrier bundles, etc) and exploit other parts of the system which otherwise were inaccessible.

Usage: patchy [-v] [-h] [-u <udid>] <application> <patch>

Options:
	-v - Set verbosity level (Incremental)
	-u - Target specific device by UDID
	-h - Prints usage information

The unmentioned MobileInstallation bugs:

When MobileInstallation installs an unpacked bundle, it will use link/unlink to move files and will fail to verify whether there are additional links present or if the files were opened by another process before placing them inside a protected container. While the permissions of the additional links will change, the owners of file descriptors on the other hand are able to keep operating on them as usual, with the same permissions they were opened with.

I advised Apple to use clonefile instead, which is essentially the same as link but applies a CoW operation to prevent modifications to the cloned file by modifying the original one, and vice versa.

Because the above vulnerabilities could have been resolved in different locations and I don't have any iOS 12.3 primitive which can directly verify this, Its still hard for me to tell whether they were addressed or not, but by the lack of a CVE I doubt it and assume only the exploited attack vectors (CVE-2019-8593, CVE-2019-8568) were addressed.

CVE-2019-8593 (AppleFileConduit):

Note that while AppleFileConduit was abused by patchy and the same issues I reported about MobileInstallation were also found in AppleFileConduit, I did not find or disclosed any issues in AppleFileConduit. I believe that while addressing the issues a use case where they can be used to cause a memory corruption was found.

Similarly to MobileInstallation (and other than the memory corruption), AppleFileConduit was missing validation of hard links and mitigations against the usage of link/unlink between the calls to AFCFileRefOpen and other AFCFileRef* APIs (e.g: AFCFileRefRead/AFCFileRefWrite).

I'm still at the process of reversing all changes and I'll report back if I was able to spot the memory corruption.

Available for: iPhone 5s and later, iPad Air and later, and iPod touch 6th generation
Impact: An application may be able to execute arbitrary code with system privileges
Description: A memory corruption issue was addressed with improved memory handling.

CVE-2019-8593: Dany Lisiansky (@DanyL931)

New Mitigations:

From what I can tell by now, there are 2 additional checks added in libafc.dylib before each operation is done:

  • File descriptors are validated to make sure only 1 link is present.
  • The location of the file is retrieved using fcntl([...], F_GETPATH) to make sure it remained within AppleFileConduit root directory boundaries.

system_app_man

A tool to download and install iOS system applications, which are tied to the device's image & build id. It was primarily used in conjunction with patchy during research

Usage: system_app_man [-v] [-h] [-u <udid>] [<url | list | download | install> [appid] [dest]]

Options:
	-v - Set verbosity level (Incremental)
	-u - Target specific device by UDID
	-h - Prints usage information

Commands:
	url				Print catalogue url
	list				Print available applications
	download <appid> <dest>		Download <appid> to <dest>
	install <appid>			Download & Install <appid>

mobile_installation_proxy and streaming_zip_conduit

Though I did not include a POC to demonstrate this, the bug can be used to exploit the other MobileInstallation issues I mentioned (see patchy section) by using mobile_installation_proxy to install unpacked bundles from an application data container.

CVE-2019-8593 (MobileInstallation, StreamingZip):

Note that the advisory wrongly described the CVE as a symlink validation issue while it was in fact a path traversal validation issue.

It looks like the issue wasn't patched in streaming_zip_conduit, which may indicate that another issue existed and was resolved instead.

Available for: iPhone 5s and later, iPad Air and later, and iPod touch 6th generation
Impact: A local user may be able to modify protected parts of the file system
Description: A validation issue existed in the handling of symlinks. This issue was addressed with improved validation of symlinks.
CVE-2019-8568: Dany Lisiansky (@DanyL931)

The faulty path resolving:

Both mobile_installation_proxy and streaming_zip_conduit implemented the following faulty method to resolve user controlled paths:

NSString *user_controlled_path = “../../“
NSString *media_path = [NSHomeDirectory() stringByAppendingPathComponent: @”Media”];
NSString *dest_path = [media_path stringByAppendingPathComponent: user_controlled_path];
NSString *resolved_dest_path = [dest_path stringByResolvingSymlinksInPath]; // <---- 'stringByResolvingSymlinksInPath' resolves only symlinks

If (![resolved_dest_path hasPrefix: media_path]) // <---- This only validate that the resolved path begins with `/var/mobile/Media'
{
	// Invalid
}

As can be seen from the pseudo code above, the resolved path may contain path traversals and still pass validation.

New Mitigations:

  • mobile_installation_proxy now uses realpath to resolve both symlinks and path traversals.

References

Credits

  • Nikias Bassen (@pimskeks) and all libimobiledevice project contributors - For providing a very well written, cross-platform protocol library to communicate with iOS devices.
  • Eric Monti - For afcclient, which was used as a reference for the AFC APIs of libimobiledevice.