# macOS Sandbox
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## Basic Information MacOS Sandbox (initially called Seatbelt) **limits applications** running inside the sandbox to the **allowed actions specified in the Sandbox profile** the app is running with. This helps to ensure that **the application will be accessing only expected resources**. Any app with the **entitlement** **`com.apple.security.app-sandbox`** will be executed inside the sandbox. **Apple binaries** are usually executed inside a Sanbox and in order to publish inside the **App Store**, **this entitlement is mandatory**. So most applications will be executed inside the sandbox. In order to control what a process can or cannot do the **Sandbox has hooks** in all **syscalls** across the kernel. **Depending** on the **entitlements** of the app the Sandbox will **allow** certain actions. Some important components of the Sandbox are: * The **kernel extension** `/System/Library/Extensions/Sandbox.kext` * The **private framework** `/System/Library/PrivateFrameworks/AppSandbox.framework` * A **daemon** running in userland `/usr/libexec/sandboxd` * The **containers** `~/Library/Containers` Inside the containers folder you can find **a folder for each app executed sanboxed** with the name of the bundle id: ```bash ls -l ~/Library/Containers total 0 drwx------@ 4 username staff 128 May 23 20:20 com.apple.AMPArtworkAgent drwx------@ 4 username staff 128 May 23 20:13 com.apple.AMPDeviceDiscoveryAgent drwx------@ 4 username staff 128 Mar 24 18:03 com.apple.AVConference.Diagnostic drwx------@ 4 username staff 128 Mar 25 14:14 com.apple.Accessibility-Settings.extension drwx------@ 4 username staff 128 Mar 25 14:10 com.apple.ActionKit.BundledIntentHandler [...] ``` Inside each bundle id folder you can find the **plist** and the **Data directory** of the App: ```bash cd /Users/username/Library/Containers/com.apple.Safari ls -la total 104 drwx------@ 4 username staff 128 Mar 24 18:08 . drwx------ 348 username staff 11136 May 23 20:57 .. -rw-r--r-- 1 username staff 50214 Mar 24 18:08 .com.apple.containermanagerd.metadata.plist drwx------ 13 username staff 416 Mar 24 18:05 Data ls -l Data total 0 drwxr-xr-x@ 8 username staff 256 Mar 24 18:08 CloudKit lrwxr-xr-x 1 username staff 19 Mar 24 18:02 Desktop -> ../../../../Desktop drwx------ 2 username staff 64 Mar 24 18:02 Documents lrwxr-xr-x 1 username staff 21 Mar 24 18:02 Downloads -> ../../../../Downloads drwx------ 35 username staff 1120 Mar 24 18:08 Library lrwxr-xr-x 1 username staff 18 Mar 24 18:02 Movies -> ../../../../Movies lrwxr-xr-x 1 username staff 17 Mar 24 18:02 Music -> ../../../../Music lrwxr-xr-x 1 username staff 20 Mar 24 18:02 Pictures -> ../../../../Pictures drwx------ 2 username staff 64 Mar 24 18:02 SystemData drwx------ 2 username staff 64 Mar 24 18:02 tmp ``` {% hint style="danger" %} Note that even if the symlinks are there to "escape" from the Sandbox and access other folders, the App still needs to **have permissions** to access them. These permissions are inside the **`.plist`**. {% endhint %} ```bash # Get permissions plutil -convert xml1 .com.apple.containermanagerd.metadata.plist -o - # In this file you can find the entitlements: Entitlements com.apple.MobileAsset.PhishingImageClassifier2 com.apple.accounts.appleaccount.fullaccess com.apple.appattest.spi [...] # Some parameters Parameters _HOME /Users/username _UID 501 _USER username [...] # The paths it can access RedirectablePaths /Users/username/Downloads /Users/username/Documents /Users/username/Library/Calendars /Users/username/Desktop [...] ``` ### Sandbox Profiles The Sandbox profiles are configuration files that indicates what is going to be **allowed/forbidden** in that **Sandbox**. It uses the **Sandbox Profile Language (SBPL)**, which uses the [**Scheme**](https://en.wikipedia.org/wiki/Scheme\_\(programming\_language\)) programming language. Here you can find an example: ```scheme (version 1) ; First you get the version (deny default) ; Then you shuold indicate the default action when no rule applies (allow network*) ; You can use wildcards and allow everything (allow file-read* ; You can specify where to apply the rule (subpath "/Users/username/") (literal "/tmp/afile") (regex #"^/private/etc/.*") ) (allow mach-lookup (global-name "com.apple.analyticsd") ) ``` {% hint style="success" %} Check this [**research**](https://reverse.put.as/2011/09/14/apple-sandbox-guide-v1-0/) **to check more actions that could be allowed or denied.** {% endhint %} Important **system services** also run inside their own custom **sandbox** such as the `mdnsresponder` service. You can view these custom **sandbox profiles** inside: * **`/usr/share/sandbox`** * **`/System/Library/Sandbox/Profiles`** * Other sandbox profiles can be checked in [https://github.com/s7ephen/OSX-Sandbox--Seatbelt--Profiles](https://github.com/s7ephen/OSX-Sandbox--Seatbelt--Profiles). **App Store** apps use the **profile** **`/System/Library/Sandbox/Profiles/application.sb`**. You can check in this profile how entitlements such as **`com.apple.security.network.server`** allows a process to use the network. SIP is a Sandbox profile called platform\_profile in /System/Library/Sandbox/rootless.conf ### Sandbox Profile Examples To start an application with an **specific sandbox profile** you can use: ```bash sandbox-exec -f example.sb /Path/To/The/Application ``` {% tabs %} {% tab title="touch" %} {% code title="touch.sb" %} ```scheme (version 1) (deny default) (allow file* (literal "/tmp/hacktricks.txt")) ``` {% endcode %} ```bash # This will fail because default is denied, so it cannot execute touch sandbox-exec -f touch.sb touch /tmp/hacktricks.txt # Check logs log show --style syslog --predicate 'eventMessage contains[c] "sandbox"' --last 30s [...] 2023-05-26 13:42:44.136082+0200 localhost kernel[0]: (Sandbox) Sandbox: sandbox-exec(41398) deny(1) process-exec* /usr/bin/touch 2023-05-26 13:42:44.136100+0200 localhost kernel[0]: (Sandbox) Sandbox: sandbox-exec(41398) deny(1) file-read-metadata /usr/bin/touch 2023-05-26 13:42:44.136321+0200 localhost kernel[0]: (Sandbox) Sandbox: sandbox-exec(41398) deny(1) file-read-metadata /var 2023-05-26 13:42:52.701382+0200 localhost kernel[0]: (Sandbox) 5 duplicate reports for Sandbox: sandbox-exec(41398) deny(1) file-read-metadata /var [...] ``` {% code title="touch2.sb" %} ```scheme (version 1) (deny default) (allow file* (literal "/tmp/hacktricks.txt")) (allow process* (literal "/usr/bin/touch")) ; This will also fail because: ; 2023-05-26 13:44:59.840002+0200 localhost kernel[0]: (Sandbox) Sandbox: touch(41575) deny(1) file-read-metadata /usr/bin/touch ; 2023-05-26 13:44:59.840016+0200 localhost kernel[0]: (Sandbox) Sandbox: touch(41575) deny(1) file-read-data /usr/bin/touch ; 2023-05-26 13:44:59.840028+0200 localhost kernel[0]: (Sandbox) Sandbox: touch(41575) deny(1) file-read-data /usr/bin ; 2023-05-26 13:44:59.840034+0200 localhost kernel[0]: (Sandbox) Sandbox: touch(41575) deny(1) file-read-metadata /usr/lib/dyld ; 2023-05-26 13:44:59.840050+0200 localhost kernel[0]: (Sandbox) Sandbox: touch(41575) deny(1) sysctl-read kern.bootargs ; 2023-05-26 13:44:59.840061+0200 localhost kernel[0]: (Sandbox) Sandbox: touch(41575) deny(1) file-read-data / ``` {% endcode %} {% code title="touch3.sb" %} ```scheme (version 1) (deny default) (allow file* (literal "/private/tmp/hacktricks.txt")) (allow process* (literal "/usr/bin/touch")) (allow file-read-data (literal "/")) ; This one will work ``` {% endcode %} {% endtab %} {% endtabs %} {% hint style="info" %} Note that the **Apple-authored** **software** that runs on **Windows** **doesn’t have additional security precautions**, such as application sandboxing. {% endhint %} Bypasses examples: * [https://lapcatsoftware.com/articles/sandbox-escape.html](https://lapcatsoftware.com/articles/sandbox-escape.html) * [https://desi-jarvis.medium.com/office365-macos-sandbox-escape-fcce4fa4123c](https://desi-jarvis.medium.com/office365-macos-sandbox-escape-fcce4fa4123c) (they are able to write files outside the sandbox whose name starts with `~$`). ### Debug & Bypass Sandbox **Processes are not born sandboxed on macOS: unlike iOS**, where the sandbox is applied by the kernel before the first instruction of a program executes, on macOS **a process must elect to place itself into the sandbox.** Processes are automatically Sandboxed from userland when they start if they have the entitlement: `com.apple.security.app-sandbox`. For a detailed explanation of this process check: {% content-ref url="macos-sandbox-debug-and-bypass.md" %} [macos-sandbox-debug-and-bypass.md](macos-sandbox-debug-and-bypass.md) {% endcontent-ref %} ### **Check PID Privileges** [According to this](https://www.youtube.com/watch?v=mG715HcDgO8\&t=3011s), the **`sandbox_check`** (it's a `__mac_syscall`), can check **if an operation is allowed or not** by the sandbox in a certain PID. The [**tool sbtool**](http://newosxbook.com/src.jl?tree=listings\&file=sbtool.c) can check if a PID can perform a certain action: ```bash sbtool mach #Check mac-ports (got from launchd with an api) sbtool file /tmp #Check file access sbtool inspect #Gives you an explaination of the sandbox profile sbtool all ``` ### Custom SBPL in App Store apps It could be possible for companies to make their apps run **with custom Sandbox profiles** (instead of with the default one). They need to use the entitlement **`com.apple.security.temporary-exception.sbpl`** which needs to be authorized by Apple. It's possible to check the definition of this entitlement in **`/System/Library/Sandbox/Profiles/application.sb:`** ```scheme (sandbox-array-entitlement "com.apple.security.temporary-exception.sbpl" (lambda (string) (let* ((port (open-input-string string)) (sbpl (read port))) (with-transparent-redirection (eval sbpl))))) ``` This will **eval the string after this entitlement** as an Sandbox profile.
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