Identifies a reverse shell via the abuse of named pipes on Linux with the help of OpenSSL or Netcat. First in, first out (FIFO) files are special files for reading and writing to by Linux processes. For this to work, a named pipe is created and passed to a Linux shell where the use of a network connection tool such as Netcat or OpenSSL has been established. The stdout and stderr are captured in the named pipe from the network connection and passed back to the shell for execution.
Rule type: eql
Risk score: 47
Runs every: 5 minutes
Maximum alerts per execution: 100
- Threat Detection
- Investigation Guide
Added (Elastic Stack release): 8.6.0
Rule authors: Elastic
Rule license: Elastic License v2
Netcat and OpenSSL are common tools used for establishing network connections and creating encryption keys. While they are popular, capturing the stdout and stderr in a named pipe pointed to a shell is anomalous.
sequence by host.id with maxspan = 5s [process where event.type == "start" and process.executable : ("/usr/bin/mkfifo","/usr/bin/mknod") and process.args:("/tmp/*","$*")] [process where process.executable : ("/bin/sh","/bin/bash") and process.args:("-i") or (process.executable: ("/usr/bin/openssl") and process.args: ("-connect"))] [process where (process.name:("nc","ncat","netcat", "netcat.openbsd","netcat.traditional") or (process.name: "openssl" and process.executable: "/usr/bin/openssl"))]