CVE-2024-3596 identifies a critical vulnerability in the RADIUS protocol as defined by IETF RFC 2865. The vulnerability stems from the use of the MD5 hashing algorithm for the Response Authenticator signature, which is susceptible to chosen-prefix collision attacks. Specifically, a local attacker with the ability to intercept and modify RADIUS responses (Access-Accept, Access-Reject, or Access-Challenge) can exploit weaknesses in MD5 to forge these responses. By generating two different inputs that produce the same MD5 hash (a chosen-prefix collision), the attacker can alter the response message without detection, effectively impersonating the RADIUS server or manipulating authentication outcomes. This attack compromises the integrity and authenticity of RADIUS responses, potentially allowing unauthorized access or denial of legitimate access. The vulnerability is classified under multiple CWEs including CWE-328 (Use of Weak Hash), CWE-200 (Exposure of Sensitive Information), CWE-924 (Improper Control of Communication Channel), and CWE-354 (Improper Validation of Integrity Check Value). The CVSS v3.1 score is 9.0 (critical), reflecting the high impact on confidentiality, integrity, and availability, with network attack vector but requiring high attack complexity and no privileges or user interaction. No patches are currently available, and no known exploits have been observed in the wild yet. The root cause is the continued reliance on MD5, a deprecated cryptographic hash function, in the RADIUS protocol specification, which is widely used for network access authentication in enterprise environments.

For European organizations, this vulnerability poses a significant risk to network access control infrastructure that relies on RADIUS authentication, which is common in enterprise Wi-Fi networks, VPNs, and other network access services. Exploitation could allow attackers to forge authentication responses, leading to unauthorized network access, data exfiltration, or disruption of services. This could result in breaches of sensitive data, violation of GDPR requirements for data protection, and operational downtime. Critical infrastructure sectors such as finance, healthcare, telecommunications, and government agencies that depend on RADIUS for secure authentication are particularly at risk. The ability to manipulate authentication responses undermines trust in network security controls and could facilitate lateral movement within networks or persistent access by threat actors. Given the network-based attack vector, exploitation could be attempted remotely if an attacker gains access to the local network segment or compromises a device within the network perimeter.

Immediate mitigation should focus on reducing reliance on MD5-based RADIUS authentication. Organizations should: 1) Transition to RADIUS implementations that support stronger cryptographic algorithms such as HMAC-SHA256 or other modern integrity mechanisms, if available. 2) Employ network segmentation and strict access controls to limit attacker access to RADIUS traffic and prevent local attackers from intercepting or modifying RADIUS responses. 3) Use IPsec or TLS tunnels to protect RADIUS traffic, ensuring confidentiality and integrity beyond the protocol's native protections. 4) Monitor RADIUS server logs and network traffic for anomalies indicative of response forgery or replay attacks. 5) Engage with vendors and standards bodies to track the availability of updated RFCs or patches that replace MD5 with secure alternatives. 6) Implement multi-factor authentication (MFA) to reduce the impact of compromised RADIUS authentication. 7) Conduct regular security assessments and penetration tests focusing on network authentication mechanisms. These steps go beyond generic advice by emphasizing cryptographic upgrades, network architecture changes, and proactive detection strategies.