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MacOS SUHelper Root Privilege Escalation Vulnerability A Deep Dive Into CVE-2022-22639
We found a now-patched vulnerability in macOS SUHelper, designated as CVE-2022-22639. If exploited, the vulnerability might enable malicious actors to achieve root privilege escalation.
By: Mickey Jin
April 04, 2022
Learn time: ( phrases)
We found a vulnerability in suhelperd, a helper daemon course of for Software program Replace in macOS. A category inside suhelperd, SUHelper, offers an important system service by way of the inter-process communication (IPC) mechanism. The method runs as root and is signed with particular entitlements, reminiscent of com.apple.rootless.set up, which grants the method permission to bypass System Integrity Safety (SIP) restrictions. This mix of functionalities presents a gorgeous alternative for malicious actors to use the vulnerability.
Designated as CVE-2022-22639, the vulnerability might enable root privilege escalation if efficiently exploited. After discovering the flaw, we reported it to Apple, therefore the discharge of a patch by way of the macOS Monterey 12.3 safety replace
This report dives into the daemon course of, enumerates all of the providers it offers, and discusses the vulnerabilities discovered therein.
The IPC service
The core logic of the daemon course of is to register an IPC service by API bootstrap_check_in, named as com.apple.suhelperd.
Determine 1. SUHelper server initialization
The consumer course of can discover the service with names by way of API bootstrap_look_up, after which request the service routines by way of the IPC mechanism. (The IPC mechanism is mentioned at size in chapter 11 of the e book “MacOS and iOS Internals, Quantity I: Consumer Mode.”)
The IPC server offers 45 service routines, a few of that are proven within the following determine. I renamed all of the routines utilizing the format IPC_NUMBER_XXX, in response to their capabilities and the corresponding rights, for simple reference.
Determine 2. Some IPC service routines
The IPC consumer is already applied within the non-public SoftwareUpdate.framework. There are 45 exported capabilities with a one-to-one correspondence to their respective service routines.
Determine 3. IPC consumer interfaces
As an alternative of reinventing the wheel, one can reuse the code from the framework. Luckily, there’s an Goal-C class named SUHelperProxy, which encapsulates all of the IPC consumer interfaces that one can instantly use.
The next is an instance of a service routine dealing with movement.
Determine 4. An IPC dealing with movement
Consumer authorization
It must be famous that not all 45 providers can be found to unprivileged shoppers, and that the server has a rights authorization mechanism to confirm if a service request is from a reputable consumer.
First, the consumer must generate an authorization object by API AuthorizationCreate, after which make it as an exterior kind (32 bytes of knowledge) to switch the authorization object to the server for verification.
Determine 5. The consumer producing the authorization object
Second, when the server receives the authorization object, it determines whether or not particular rights may be granted to the consumer. At this stage, the server checks the consumer’s authorization object and uid.
Determine 6. The server verifying the consumer’s authorization object and uid
Third, when the consumer requests a particular service routine, the server checks whether or not the particular rights have been beforehand granted to the consumer, in any other case it denies the request.
Previous vulnerabilities
As talked about earlier, not all of the service routines are allowed due to the requisite consumer authorization. Nonetheless, there have been some important routines that have been left unprotected as a result of the server didn’t validate the rights on the third step.
Listed below are two previous vulnerabilities, for instance, which have been found by researchers at Xuanwu Lab. CVE-2021-30913 might enable malicious actors to edit NVRAM variables.
Determine 7. CVE-2021-30913 particulars
The vulnerability exists within the caller operate of the operate “-[SUHelper setNVRAMWithKey:value:]”. Its patch provides the validation code at line 9.
Determine 8. The patch of CVE-2021-30913
It validates the consumer rights with worth 2, so I renamed the caller operate as IPC_2_setNVRAMWithKey_value to mark the wanted rights.
Subsequent is CVE-2021-30912, a vulnerability that would grant malicious actors entry to a person’s Keychain objects.
Determine 9. CVE-2021-30912 particulars
The vulnerability exists within the caller operate of the operate “-[SUHelper lookupURLCredentialInSystemKeychainForHost:port:]”.
Its patch provides the validation code at line 10.
Determine 10. The patch of CVE-2021-30912
New discovering: CVE-2022-22639
After reviewing the 45 service routines, I filtered out these with validation codes and located a couple of that had names beginning with “IPC_0_”. A detailed inspection of those routines revealed that the operate “-[SUHelper prepareInstallAssistantWithPath:(NSString *) path]” was exploitable. The caller operate IPC_0_prepareInstallAssistantWithPath didn’t validate the consumer’s rights and known as the true routine instantly.
Determine 11. A weak IPC service routine
The implementation of the operate is as follows, with the third parameter (NSString *) path that’s handed from the consumer.
Determine 12. The implementation of the operate “–[SUHelper prepareInstallAssitantWithPath:]”
A have a look at the interior operate reveals that it hundreds a bundle at line 70.
Determine 13. The inner operate implementation
I debugged and located the bundle path as ${Assistant.app}/Contents/Frameworks/OSInstallerSetup.framework. An necessary discovering is that the ${Assistant.app} is definitely the third parameter (NSString *) path, which may be fully managed by the consumer.
In a traditional situation, the ${Assistant.app} must be the true path to “Set up macOS XXX.app”. It’s extracted from InstallAssistant.pkg, which is downloaded from the Apple server. Nonetheless, I found {that a} person might faux the trail and contents of the ${Assistant.app} by exploiting this vulnerability.
Plainly I discovered a primitive to load any dylib into the goal course of to get the foundation privilege and the particular entitlements. Nonetheless, I didn’t load a self-signed dylib instantly as a result of I discovered that hardened runtime is enabled by default for system processes when SIP is on, despite the fact that it isn’t signed with runtime flags. However I might load arbitrary Apple-signed dylib into it even when it was an previous, weak dylib.
Maybe there are different strategies to use the problem. Right here, I let it load the unique OSInstallerSetup.framework. As soon as the OSInstallerSetup.framework is loaded, it calls the operate “-[OSISClient _startServer]”. At line 103, it launches one other IPC service, com.apple.set up.osinstallersetupd, by API SMJobSubmit. From line 48, it may be seen that if the present course of is working as root, the newly submitted job runs at system area with root privileges too.
Determine 14. The implementation of the operate “–[OSISClient _startServer]”
Now, the present course of is suhelperd, working as root, and the job executable path is toolPath, which is contained in the bundle ${Assistant.app}/Contents/Frameworks/OSInstallerSetup.framework/Sources/osinstallersetupd. A malicious actor might put the payload in toolPath instantly to realize root privilege escalation.
Determine 15. The right way to get the toolPath
The complete proof of idea may be discovered right here and a video demonstration may be considered right here.
Patch
As talked about earlier, Apple has addressed the CVE-2022-22639 difficulty by way of the macOS Monterey 12.3 safety replace. This patch now provides the validation code at line 9.
Determine 16. The patch of CVE-2022-22639
Safety suggestions
Finish-users can mitigate the dangers by commonly updating methods and functions with the most recent patches to make sure that safety flaws can’t be exploited for malicious actions.
Study Development Micro™ Most Safety for Mac so you’ll be able to take pleasure in your digital life safely. It blocks viruses, spy ware, ransomware, and different malicious software program on your peace of thoughts.
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