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We found a now-patched vulnerability in macOS SUHelper, designated as CVE-2022-22639. If exploited, the vulnerability may permit malicious actors to realize root privilege escalation.
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 via the inter-process communication (IPC) mechanism. The method runs as root and is signed with particular entitlements, akin to com.apple.rootless.set up, which grants the method permission to bypass System Integrity Safety (SIP) restrictions. This mix of functionalities presents a lovely alternative for malicious actors to use the vulnerability.
Designated as CVE-2022-22639, the vulnerability may permit root privilege escalation if efficiently exploited. After discovering the flaw, we reported it to Apple, therefore the discharge of a patch via the macOS Monterey 12.3 safety replace
This report dives into the daemon course of, enumerates all of the companies 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.
The shopper course of can discover the service with names via API bootstrap_look_up, after which request the service routines via the IPC mechanism. (The IPC mechanism is mentioned at size in chapter 11 of the guide “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 features and the corresponding rights, for straightforward reference.
The IPC shopper is already applied within the personal SoftwareUpdate.framework. There are 45 exported features with a one-to-one correspondence to their respective service routines.
As an alternative of reinventing the wheel, one can reuse the code from the framework. Happily, there may be an Goal-C class named SUHelperProxy, which encapsulates all of the IPC shopper interfaces that one can straight use.
The next is an instance of a service routine dealing with stream.
Consumer authorization
It must be famous that not all 45 companies can be found to unprivileged purchasers, and that the server has a rights authorization mechanism to confirm if a service request is from a professional shopper.
First, the shopper must generate an authorization object by API AuthorizationCreate, after which make it as an exterior type (32 bytes of knowledge) to switch the authorization object to the server for verification.
Second, when the server receives the authorization object, it determines whether or not particular rights will be granted to the shopper. At this stage, the server checks the shopper’s authorization object and uid.
Third, when the shopper requests a particular service routine, the server checks whether or not the particular rights have been beforehand granted to the shopper, 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 shopper 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 here are two previous vulnerabilities, for instance, which have been found by researchers at Xuanwu Lab. CVE-2021-30913 may permit malicious actors to edit NVRAM variables.
The vulnerability exists within the caller perform of the perform “-[SUHelper setNVRAMWithKey:value:]”. Its patch provides the validation code at line 9.
It validates the shopper rights with worth 2, so I renamed the caller perform as IPC_2_setNVRAMWithKey_value to mark the wanted rights.
Subsequent is CVE-2021-30912, a vulnerability that might grant malicious actors entry to a person’s Keychain objects.
The vulnerability exists within the caller perform of the perform “-[SUHelper lookupURLCredentialInSystemKeychainForHost:port:]”.
Its patch provides the validation code at line 10.
New discovering: CVE-2022-22639
After reviewing the 45 service routines, I filtered out these with validation codes and located just a few that had names beginning with “IPC_0_”. An in depth inspection of those routines revealed that the perform “-[SUHelper prepareInstallAssistantWithPath:(NSString *) path]” was exploitable. The caller perform IPC_0_prepareInstallAssistantWithPath didn’t validate the shopper’s rights and known as the true routine straight.
The implementation of the perform is as follows, with the third parameter (NSString *) path that’s handed from the shopper.
![Figure 12. The implementation of the function “–[SUHelper prepareInstallAssitantWithPath:]”](https://www.trendmicro.com/content/dam/trendmicro/global/en/research/22/d/suhelper/suhelper12.png)
A have a look at the inner perform reveals that it hundreds a bundle at line 70.
I debugged and located the bundle path as ${Assistant.app}/Contents/Frameworks/OSInstallerSetup.framework. An vital discovering is that the ${Assistant.app} is definitely the third parameter (NSString *) path, which will be fully managed by the shopper.
In a traditional state of affairs, 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 may 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 basis privilege and the particular entitlements. Nonetheless, I did not load a self-signed dylib straight as a result of I discovered that hardened runtime is enabled by default for system processes when SIP is on, though it isn’t signed with runtime flags. However I may load arbitrary Apple-signed dylib into it even when it was an previous, susceptible 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 perform “-[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.
![Figure 14. The implementation of the function “–[OSISClient _startServer]”](https://www.trendmicro.com/content/dam/trendmicro/global/en/research/22/d/suhelper/suhelper14.png)
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 may put the payload in toolPath straight to achieve root privilege escalation.
The complete proof of idea will be discovered right here and a video demonstration will be considered right here.
Patch
As talked about earlier, Apple has addressed the CVE-2022-22639 difficulty via the macOS Monterey 12.3 safety replace. This patch now provides the validation code at line 9.
Safety suggestions
Finish-users can mitigate the dangers by usually updating techniques and purposes with the newest patches to make sure that safety flaws can’t be exploited for malicious actions.
Study Pattern Micro™ Most Safety for Mac so you may take pleasure in your digital life safely. It blocks viruses, adware, ransomware, and different malicious software program in your peace of thoughts.
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