External risk intelligence

RADIUS Protocol Forgery Attack via Chosen-Prefix Collision on MD5 Authenticator

CVE advisorySeverity: CRITICAL (CVSS 9.0)

CVE-2024-3596

The vulnerability involves the RADIUS protocol, which is primarily used for internal network authentication (AAA) and is typically deployed behind firewalls or within private, isolated management networks. While network-reachable in some enterprise environments, RADIUS is not designed or intended to be exposed directly to the public internet, making public internet exposure uncommon in standard deployments.

Freeradius

before 3.0.27

Halo Surface Signal: 2 out of 5 — less likely to be public-facing.

External exposure likelihood

Horizon Alert

Summary of the vulnerability and why it matters

A vulnerability has been identified within the RADIUS protocol, a system used for network authentication, authorization, and accounting. This issue could allow a local attacker to manipulate authentication responses, potentially impacting network access controls. The main concern is confirming relevance and exposure within your specific environment.

Authentication responses can be forged.
Understand potential network access risks.
Assess if RADIUS is used in your network.

Attack Path

How an attacker could exploit the issue

An attacker with the ability to intercept and modify network traffic can exploit a weakness in the RADIUS protocol's signature verification. By forging valid responses, an attacker could potentially impersonate legitimate users or services, leading to unauthorized access or manipulation of network resources. This attack requires a specific type of cryptographic collision to succeed.

Attacker can modify valid RADIUS responses.
Vulnerability is triggered by a chosen-prefix collision.
Risk includes forged authentication and unauthorized access.

Live Threat

Current exploitation, exposure, and threat context

A local attacker who can modify RADIUS responses could forge valid authentication responses, potentially allowing unauthorized access to network resources when supported by the advisory.

RADIUS protocol authentication responses.
Forgery attacks on response authenticator.
Unauthorized network access.

Operational Fix

Recommended remediation, mitigation, and detection steps

This vulnerability likely impacts infrastructure and network teams responsible for authentication services, and potentially vendor management if commercial RADIUS solutions are used. The first practical step is to identify all RADIUS servers within the environment, confirm their network exposure, and determine their criticality to business operations before planning any remediation actions.

Network and infrastructure teams own remediation.
Verify RADIUS server reachability and criticality.
Plan remediation based on identified risks.

Supplementary metadata

CVSS vector

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Frequently asked questions

What is the RADIUS protocol used for in network environments?

RADIUS is a foundational networking protocol used for Authentication, Authorization, and Accounting (AAA). Organizations rely on it to manage user access to networks and devices, ensuring that only verified individuals or services can connect to resources. Common implementations include FreeRADIUS software and various hardware-based solutions, like those from SonicWall and Broadcom, which facilitate secure network sign-ins.

What does the MD5 vulnerability in CVE-2024-3596 actually mean?

This CVE involves a weakness categorized as CWE-354 (Improper Validation of Integrity Check Value). Essentially, the way RADIUS verifies the authenticity of its messages relies on an older cryptographic hash, MD5. An attacker can exploit this to create a 'collision,' where they mathematically manipulate the response data to forge a valid-looking authentication message. This allows them to effectively trick the system into accepting fraudulent access requests.

Do I need to be physically present on the network to trigger this?

The attack requires the ability to intercept and modify RADIUS traffic between the client and the server. It is not triggered by simply visiting a website or sending standard user data. The attacker must be positioned in a way that they can actively manipulate packets as they traverse the network path, making it a sophisticated maneuver rather than a simple automated script.

Is my RADIUS server likely to be reachable by external attackers?

Halo Surface Signal indicates that exploitation is unlikely for most organizations because RADIUS is typically confined to internal, private management networks. Because it is rarely intended to be directly exposed to the public internet, it sits behind protective layers. However, you should verify that your specific RADIUS deployments are not inadvertently reachable from outside your network perimeter.

How should I respond to the CVE-2024-3596 advisory?

Your first step is to inventory your environment to locate all active RADIUS servers and identify the vendors managing them. Prioritize these assets based on their criticality to your operations. Once identified, work with your infrastructure teams to assess their network reachability and prepare for vendor-supplied patches or configuration changes designed to mitigate the risks associated with this protocol weakness.

References

Written by Nicholas Merritt

Nicholas Merritt is VP of Security Solutions at Halo Security. With more than 25 years across application security, vulnerability prioritization, and offensive security, he helps teams translate threat data into practical exposure validation and remediation focus. He authors Halo Threat Intelligence CVE advisories using Halo Surface Signal and H/A/L/O context to prioritize internet-facing risk.