13 KiB
macOS SIP
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Basic Information
System Integrity Protection (SIP) is a security technology in macOS that safeguards certain system directories from unauthorized access, even for the root user. It prevents modifications to these directories, including creation, alteration, or deletion of files. The main directories that SIP protects are:
- /System
- /bin
- /sbin
- /usr
The protection rules for these directories and their subdirectories are specified in the /System/Library/Sandbox/rootless.conf
file. In this file, paths starting with an asterisk (*) represent exceptions to SIP's restrictions.
For instance, the following configuration:
javascriptCopy code/usr
* /usr/libexec/cups
* /usr/local
* /usr/share/man
indicates that the /usr
directory is generally protected by SIP. However, modifications are allowed in the three subdirectories specified (/usr/libexec/cups
, /usr/local
, and /usr/share/man
), as they are listed with a leading asterisk (*).
To verify whether a directory or file is protected by SIP, you can use the ls -lOd
command to check for the presence of the restricted
or sunlnk
flag. For example:
ls -lOd /usr/libexec/cups
drwxr-xr-x 11 root wheel sunlnk 352 May 13 00:29 /usr/libexec/cups
In this case, the sunlnk
flag signifies that the /usr/libexec/cups
directory itself cannot be deleted, though files within it can be created, modified, or deleted.
On the other hand:
ls -lOd /usr/libexec
drwxr-xr-x 338 root wheel restricted 10816 May 13 00:29 /usr/libexec
Here, the restricted
flag indicates that the /usr/libexec
directory is protected by SIP. In a SIP-protected directory, files cannot be created, modified, or deleted.
SIP Status
You can check if SIP is enabled on your system with the following command:
csrutil status
If you need to disable SIP, you must restart your computer in recovery mode (by pressing Command+R during startup), then execute the following command:
csrutil disable
If you wish to keep SIP enabled but remove debugging protections, you can do so with:
csrutil enable --without debug
Other Restrictions
SIP also imposes several other restrictions. For instance, it disallows the loading of unsigned kernel extensions (kexts) and prevents the debugging of macOS system processes. It also inhibits tools like dtrace from inspecting system processes.
SIP Bypasses
Prices
If an attacker manages to bypass SIP this is what he will earn:
- Read mail, messages, Safari history... of all users
- Grant permissions for webcam, microphone or anything (by directly writing over the SIP protected TCC database)
- Persistence: He could save a malware in a SIP protected location and not even toot will be able to delete it. Also he could tamper with MRT.
- Easiness to load kernel extensions (still other hardcore protections in place for this).
Installer Packages
Installer packages signed with Apple's certificate can bypass its protections. This means that even packages signed by standard developers will be blocked if they attempt to modify SIP-protected directories.
Unexistent SIP file
One potential loophole is that if a file is specified in rootless.conf
but does not currently exist, it can be created. Malware could exploit this to establish persistence on the system. For example, a malicious program could create a .plist file in /System/Library/LaunchDaemons
if it is listed in rootless.conf
but not present.
com.apple.rootless.install.heritable
{% hint style="danger" %}
The entitlement com.apple.rootless.install.heritable
allows to bypass SIP
{% endhint %}
Researchers from this blog post discovered a vulnerability in macOS's System Integrity Protection (SIP) mechanism, dubbed the 'Shrootless' vulnerability. This vulnerability centers around the system_installd
daemon, which has an entitlement, com.apple.rootless.install.heritable
, that allows any of its child processes to bypass SIP's file system restrictions.
Researchers found that during the installation of an Apple-signed package (.pkg file), system_installd
runs any post-install scripts included in the package. These scripts are executed by the default shell, zsh
, which automatically runs commands from the /etc/zshenv
file, if it exists, even in non-interactive mode. This behavior could be exploited by attackers: by creating a malicious /etc/zshenv
file and waiting for system_installd
to invoke zsh
, they could perform arbitrary operations on the device.
Moreover, it was discovered that /etc/zshenv
could be used as a general attack technique, not just for a SIP bypass. Each user profile has a ~/.zshenv
file, which behaves the same way as /etc/zshenv
but doesn't require root permissions. This file could be used as a persistence mechanism, triggering every time zsh
starts, or as an elevation of privilege mechanism. If an admin user elevates to root using sudo -s
or sudo <command>
, the ~/.zshenv
file would be triggered, effectively elevating to root.
In CVE-2022-22583 it was discovered that the same system_installd
process could still be abused because it was putting the post-install script inside a random named folder protected by SIP inside /tmp
. The thing is that /tmp
itself isn't protected by SIP, so it was possible to mount a virtual image on it, then the installer would put in there the post-install script, unmount the virtual image, recreate all the folders and add the post installation script with the payload to execute.
com.apple.rootless.install
{% hint style="danger" %}
The entitlement com.apple.rootless.install
allows to bypass SIP
{% endhint %}
From CVE-2022-26712 The system XPC service /System/Library/PrivateFrameworks/ShoveService.framework/Versions/A/XPCServices/SystemShoveService.xpc
has the entitlement com.apple.rootless.install
, which grants the process permission to bypass SIP restrictions. It also exposes a method to move files without any security check.
Sealed System Snapshots
Sealed System Snapshots are a feature introduced by Apple in macOS Big Sur (macOS 11) as a part of its System Integrity Protection (SIP) mechanism to provide an additional layer of security and system stability. They are essentially read-only versions of the system volume.
Here's a more detailed look:
- Immutable System: Sealed System Snapshots make the macOS system volume "immutable", meaning that it cannot be modified. This prevents any unauthorized or accidental changes to the system that could compromise security or system stability.
- System Software Updates: When you install macOS updates or upgrades, macOS creates a new system snapshot. The macOS startup volume then uses APFS (Apple File System) to switch to this new snapshot. The entire process of applying updates becomes safer and more reliable as the system can always revert to the previous snapshot if something goes wrong during the update.
- Data Separation: In conjunction with the concept of Data and System volume separation introduced in macOS Catalina, the Sealed System Snapshot feature makes sure that all your data and settings are stored on a separate "Data" volume. This separation makes your data independent from the system, which simplifies the process of system updates and enhances system security.
Remember that these snapshots are automatically managed by macOS and don't take up additional space on your disk, thanks to the space sharing capabilities of APFS. It’s also important to note that these snapshots are different from Time Machine snapshots, which are user-accessible backups of the entire system.
Check Snapshots
The command diskutil apfs list
lists the details of the APFS volumes and their layout:
+-- Container disk3 966B902E-EDBA-4775-B743-CF97A0556A13
| ====================================================
| APFS Container Reference: disk3
| Size (Capacity Ceiling): 494384795648 B (494.4 GB)
| Capacity In Use By Volumes: 219214536704 B (219.2 GB) (44.3% used)
| Capacity Not Allocated: 275170258944 B (275.2 GB) (55.7% free)
| |
| +-< Physical Store disk0s2 86D4B7EC-6FA5-4042-93A7-D3766A222EBE
| | -----------------------------------------------------------
| | APFS Physical Store Disk: disk0s2
| | Size: 494384795648 B (494.4 GB)
| |
| +-> Volume disk3s1 7A27E734-880F-4D91-A703-FB55861D49B7
| | ---------------------------------------------------
| | APFS Volume Disk (Role): disk3s1 (System)
| | Name: Macintosh HD (Case-insensitive)
| | Mount Point: /System/Volumes/Update/mnt1
| | Capacity Consumed: 12819210240 B (12.8 GB)
| | Sealed: Broken
| | FileVault: Yes (Unlocked)
| | Encrypted: No
| | |
| | Snapshot: FAA23E0C-791C-43FF-B0E7-0E1C0810AC61
| | Snapshot Disk: disk3s1s1
| | Snapshot Mount Point: /
| | Snapshot Sealed: Yes
[...]
In the previous output it's possible to see that macOS System volume snapshot is sealed (cryptographically signed by the OS). SO, if SIP is bypassed and modifies it, the OS won't boot anymore.
It's also possible to verify that seal is enabled by running:
csrutil authenticated-root status
Authenticated Root status: enabled
Moreover, it's mounted as read-only:
mount
/dev/disk3s1s1 on / (apfs, sealed, local, read-only, journaled)
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- Get the official PEASS & HackTricks swag
- Join the 💬 Discord group or the telegram group or follow me on Twitter 🐦@carlospolopm.
- Share your hacking tricks by submitting PRs to the hacktricks repo and hacktricks-cloud repo.