A new vulnerability, which we refer to as “Migraine” for its involvement with macOS migration, could allow an attacker with root access to automatically bypass System Integrity Protection (SIP) in macOS and perform arbitrary operations on a device. We shared these findings with Apple through Coordinated Vulnerability Disclosure (CVD) via Microsoft Security Vulnerability Research (MSVR). A fix for this vulnerability, now identified as CVE-2023-32369, was included in the security updates released by Apple on May 18, 2023.
SIP is a security technology in macOS that restricts a root user from performing operations that may compromise system integrity. Bypassing SIP could lead to serious consequences, such as increasing the potential for attackers and malware authors to successfully install rootkits, create persistent malware, and expand the attack surface for additional techniques and exploits. The technique uncovered in this blog post was discovered during routine malware hunting and is similar to the one used in the Shrootless vulnerability (CVE-2021-30892) that we published in 2021. By focusing on system processes that are signed by Apple and have the com.apple.rootless.install.heritable entitlement, we found two child processes that could be tampered with to gain arbitrary code execution in a security context that bypasses SIP checks.
In this blog post, we share some information about the relationship between SIP and entitlements, and we detail how the “Migraine” vulnerability could be exploited to bypass the SIP security enforcements. We’re sharing this research with the larger security community to emphasize the importance of collaboration in the effort to secure platforms and devices.
As previously covered in our Shrootless vulnerability blog post, System Integrity Protection (SIP)—also known as “rootless”—was first introduced by Apple in macOS Yosemite. SIP essentially locks down the system from root by leveraging the Apple sandbox to protect the entire platform, conceptually similar to how SELinux protects Linux systems. One of the most dominant features of SIP is the filesystem restriction capability, which protects entire files and directories from being overridden. The files and directories that are protected by SIP by default are commonly ones that are related to the system’s integrity.
There is no way to turn off SIP on a live system—the user must use the recovery OS, which requires physical access to the device. A SIP bypass is a vulnerability that bypasses SIP restrictions, for example, bypassing restrictions to write to SIP-protected directories or create a SIP-protected file.
Another important macOS concept is entitlements. According to documentation, “an entitlement is a right or privilege that grants an executable particular capabilities”. As entitlements take part in the app signing process, there is no legitimate way of forging them. Apple uses entitlements extensively to enforce security on macOS, and Apple grants internal entitlements to very specific processes. Specifically, certain processes are assigned entitlements that allow the process to bypass System Integrity Protection checks by design. One particularly interesting entitlement is the com.apple.rootless.install.heritable entitlement that allows the process and the entire process tree rooted under it to bypass filesystem-based System Integrity Protection security enforcements.
Our research team regularly looks for malware and suspicious activity. During a routine malware hunt, we discovered the execution of a binary called drop_sip using the below advanced hunting query in Microsoft 365 Defender:
DeviceProcessEvents
| where FileName =~ "drop_sip"
| project InitiatingProcessFileName, ProcessCommandLine, SHA256
Thinking that we found an exploit in the wild, we found that it’s an Apple-signed binary that resides natively under the /System/Library/PrivateFrameworks/SystemMigrationUtils.framework/Resources/Tools/drop_sip path.
Upon analysis, the file appears to invoke the csops system call (undocumented, but available here) and starts a child process. The operation flag for the csops call is 12 (CS_OPS_CLEARINSTALLER), which re-enables SIP checks by clearing codesigning flags, specifically the CS_EXEC_INHERIT_SIP flag:
Because of this behavior, we concluded the drop_sip process assumes it can bypass SIP. However, since drop_sip is not entitled with any SIP-bypassing entitlements, we concluded that it must inherit that capability. We discovered its parent process is systemmigrationd, which is a daemon designed to handle migration scenarios, but most importantly, it’s entitled with the com.apple.rootless.install.heritable entitlement that allows its child processes to bypass SIP security checks:
After discovering the parent process of drop_sip, we wondered if there are any other child processes of systemmigrationd. Just as before, we used the below advanced hunting query in Microsoft 365 Defender:
DeviceProcessEvents
| where InitiatingProcessFileName =~ "systemmigrationd"
| summarize Hits=count(), Cmdline=any(ProcessCommandLine) by FileName
We found two interesting child processes of systemmigrationd:
| FileName | Hits | Cmdline |
| bash | 498 | /bin/bash /System/Library/PrivateFrameworks/SystemMigration.framework/Resources/MigrationData/Scripts/firstbootDirectoryServer |
| perl | 171 | /usr/bin/perl /usr/libexec/migrateLocalKDC –source “/Volumes/REDACTED/Backups.backupdb/REDACTED/Macintosh HD – Data” –source-REDACTED |
The bash and perl binaries are interesting because they are both interpreters. Similar to how we tampered with the zsh codeflow back in 2021, we found similar ways to tamper with the code flow of bash and perl:
Assuming an attacker first gains code execution capabilities as root, setting environment variables that affect systemmigrationd and its child processes is straightforward using the launchctl utility. For instance, to make perl run our arbitrary code that resides under /private/tmp/migraine.sh, we use:
launchctl setenv PERL5OPT '-Mwarnings;system("/private/tmp/migraine.sh")'
And indeed, after triggering systemmigrationd to run perl, we were able to bypass SIP:
Triggering migration normally requires using the Migration Assistant utility, which involves a complete sign-out from the system. While this works well for attackers with physical access (hands-on-keyboard), we wished to demonstrate that remote attackers can achieve a SIP bypass using this exploit. Therefore, we decided to research the migration flow and the interplay between the Migration Assistant and systemmigrationd.
Migration is a complicated procedure that involves several components. Here is the flow of key events:
This complex flow can be illustrated with the following schematic:
Our first attempt at automating the exploit focused on patching Migration Assistant to prevent user sign-out:
Simply patching Migration Assistant does not work due to codesign failure. Stripping the binary of signing information results in error (Figure 10) due to a kernel feature related to Pointer Authentication Codes (PAC) that’s available for the latest Apple Silicone architecture. If an arm64e binary with pointer authentication is not a code-signed platform binary, the kernel prevents execution, as shown in Figure 9. Extracting, stripping, and patching the x64 portion of the multiarchitecture binary avoids the arm64e issue, but it’s not functional due to losing the required entitlement (com.apple.private.mbsystemadministration).
After reaching an impasse with patching Migration Assistant, we wondered if we could initiate later stages in the flow diagram, thus avoiding user sign-out. We continued to map and reverse-engineer the system behavior, including using an in-house researcher tool which leverages the Endpoint Security Framework that logs all relevant process and file events during migration, inspired by Patrick Wardle’s FileMonitor and ProcessMonitor tools for investigating system behaviors.
While mapping the sequence of events for Migration Assistant, MBSystemAdministration, Setup Assistant, and systemmigrationd, we noticed xpcproxy executing Setup Assistant with the argument ‑MiniBuddyYes.
Running Setup Assistant with that argument had no effect on the UI layout or its functionality, but it did highlight the usage of arguments within Setup Assistant. Closely examining Setup Assistant, we discovered other interesting command-line arguments:
Additionally, we discovered a function called useDebugParameters that parses an interesting command-line parameter ‑MBDebug.
Running the Setup Assistant with the ‑MBDebug parameter results in a successful migration with no sign out. We further used the -ResumeBuddyYes parameter in conjunction with ‑MBDebug to automatically skip a few welcome screens.
Since performing migration requires UI interaction, but no sign-out, we used AppleScript to automate the exploit.
Our final exploit does the following:
The implications of arbitrary SIP bypasses are serious, as the potential for malware authors is significant. Code that maliciously bypasses SIP could have considerable consequences, such as:
Attackers continue to seek new footholds into increasingly secure devices and networks, oftentimes by leveraging unpatched vulnerabilities and misconfigurations to access valuable systems and data. Gaining the ability to bypass SIP and similar security technology in macOS devices can be an attractive and even necessary capability for adversaries. Given SIP’s position as both a device’s built-in baseline protection and the last line of defense against malware and other threats, bypassing SIP can have considerable consequences for users. As such, it’s crucial that we strive to enrich our protection technologies across platforms against such issues through research-driven protection and collaboration with partners, customers, and industry experts.
This case displays how collaborative research and responsible vulnerability disclosure informs our comprehensive protection capabilities across platforms to provide organizations a complete picture of their security posture. Microsoft Defender Vulnerability Management quickly discovers and remediates such vulnerabilities while Microsoft Defender for Endpoint detects and alerts on anomalous device activities, including setting perl and bash environment variables through the launchctl utility, as shown below in Figure 15. Additionally, Defender for Endpoint has similar detections for sensitive file access, including system launch daemons, various sensitive configuration files, and many more.
This case further emphasizes the need for responsible vulnerability disclosures and expert cross-platform collaboration to mitigate issues such as CVE-2023-32369, regardless of the vulnerable device or platform in use. We wish to thank the Apple product security team again for their efforts and responsiveness in addressing the issue.
Defending against the evolving threat landscape requires the ability to protect and secure users’ computing experiences, whatever the platform. As cross-platform threats continue to grow, we will continue to share vulnerability discoveries and threat intelligence in addition to working with the security community to improve upon solutions that protect users and organizations each day.
Jonathan Bar Or, Michael Pearse, Anurag Bohra
Microsoft Threat Intelligence Community
Microsoft Threat Intelligence uncovered a macOS vulnerability that could potentially allow an attacker to bypass the operating system’s Transparency, Consent, and Control (TCC) technology and gain unauthorized access to a user’s protected data. The vulnerability, which we refer to as “HM Surf”, involves removing the TCC protection for the Safari browser directory and modifying a […]
Microsoft researchers found multiple vulnerabilities in OpenVPN that could lead to an attack chain allowing remote code execution and local privilege escalation. This attack chain could enable attackers to gain full control over targeted endpoints, potentially resulting in data breaches, system compromise, and unauthorized access to sensitive information.
A set of memory corruption vulnerabilities in the ncurses library could have allowed attackers to chain the vulnerabilities to elevate privileges and run code in the targeted program's context or perform other malicious actions.
Microsoft discovered a vulnerability in macOS, referred to as “Achilles”, allowing attackers to bypass application execution restrictions enforced by the Gatekeeper security mechanism.