Remote Authentication Dial-In User Service (RADIUS) is a protocol originally developed for use by internet service providers (ISPs) and is widely used in applications such as corporate networks, Wi-Fi, VPNs and other types of remote access.
Despite the protocol’s widespread use and importance in network security, the RADIUS protocol is not without its vulnerabilities. Problems such as the use of older encryption algorithms, the lack of protection against man-in-the-middle attacks and the possibility of credential capture are some of the security challenges that need to be considered.
In this blog, we will explore these vulnerabilities and discuss how to mitigate them to ensure a more secure network environment.
How does the RADIUS protocol work in practice?
In the first stage, RADIUS checks the credentials of the user trying to access the network. The second stage is authorization, where the protocol determines which resources or services the authenticated user can access. This is followed by accounting, where the server records information about the user’s session.
In this context, the operation of RADIUS involves the interaction between three main components: the RADIUS client, the RADIUS server and the authentication database.
RADIUS client: this is usually the network device to which the user is trying to connect, such as a Wi-Fi access point, a VPN server or a switch. When the user tries to access the network, the RADIUS client sends the user’s credentials (e.g. username and password) to the RADIUS server for validation.
RADIUS server: this is the core of the process. The server receives the request from the RADIUS client and compares it with the information stored in the authentication database. Depending on the configuration, this database can be local or external, such as an LDAP directory or Active Directory. The RADIUS server checks the credentials and, if they are valid, moves on to the authorization stage.
Authorization and Response: after checking the credentials, the RADIUS server decides which resources or services the authenticated user can access. Authorization policies can include access to certain networks, bandwidth limitations, or time restrictions. The server then sends a response to the RADIUS client, approving or denying access. If approved, the RADIUS client grants access to the user.
Accounting: during the user’s session, the RADIUS server monitors and records details about network usage, such as connection time and volume of data trafficked. This information is essential for auditing purposes, monitoring usage or even charging for services in environments where network access is charged for.
In short, RADIUS acts as a trusted intermediary between the user and the network, ensuring that only authorized users can access specific resources.
What are the vulnerabilities of the RADIUS protocol?
Despite the fact that it has a strong structure, the vulnerabilities inherent in the RADIUS protocol can compromise network security if they are not properly addressed. See what these vulnerabilities are and how to mitigate them:
- Weak encryption
RADIUS uses the MD5 hash algorithm to protect passwords during transmission. However, MD5 has been considered insecure for many years due to its susceptibility to collision attacks, where different entries can produce the same hash, allowing an attacker to crack the password.
In addition, the protocol only encrypts the user’s password in the authentication request, but other sensitive information such as username, IP address and authorization details are transmitted in clear text. This allows an attacker, if they intercept the traffic, to obtain this information.
- Vulnerability to Man-in-the-Middle (MitM) attacks
On networks without adequate protection, such as open or poorly configured Wi-Fi networks, an attacker can carry out a Man-in-the-Middle attack by intercepting the communication between the RADIUS client and the server. This allows the attacker to capture and manipulate credentials or other transmitted data.
- Lack of strong server authentication
The RADIUS protocol does not strongly authenticate the server to which the client is connecting. If an attacker manages to insert a fake RADIUS server into the network, they can capture users’ authentication credentials.
- Implementation and configuration problems
RADIUS uses secret keys shared between the client and the server to protect communication. However, these keys are often improperly configured, such as being too short, predictable or reused on multiple devices, facilitating attacks.
In addition, many administrators leave the default RADIUS settings unchanged, which can include weak passwords or inadequate security settings that make the network vulnerable to attacks.
- Dictionary and brute force attacks
As RADIUS uses MD5 to protect passwords, an attacker can carry out dictionary or brute force attacks to try to guess the password, especially if the passwords are short or common.
- Vulnerability to eavesdropping
In networks that do not use transport layer encryption (such as TLS), it is possible for an attacker to capture RADIUS packets and obtain sensitive information or even inject false commands into the communication.
- Scalability and administration
In large networks, administering secret keys and authorization policies for all devices and users can become complicated, leading to configuration errors that open up security loopholes.
- Does not natively support multifactor authentication (MFA)
RADIUS was developed before the advent of modern security practices such as multifactor authentication (MFA). Although there are extensions and solutions that integrate MFA into RADIUS, the protocol itself does not offer native support for more secure authentication methods.
How can these vulnerabilities be mitigated?
To mitigate the vulnerabilities of the RADIUS protocol, it is essential to adopt a series of security practices to strengthen network protection.
The first measure is to replace the use of the MD5 algorithm with more robust encryption methods, such as using IPsec or Transport Layer Security (TLS) to encrypt all communication between the client and the RADIUS server. This ensures that not only passwords but also other sensitive information is protected from interception.
Another fundamental practice is to implement multifactor authentication (MFA). Although RADIUS does not support MFA natively, it is possible to integrate it with authentication systems that offer this additional layer of security. This makes brute force or dictionary attacks significantly more difficult, because even if the credentials are compromised, the attacker would still need a second authentication factor to gain access.
In addition, protection against Man-in-the-Middle (MitM) attacks can be improved by ensuring that communication between the client and the RADIUS server takes place over a secure network and by using digital certificates to authenticate the server. This prevents an attacker from inserting a fake server into the network to capture credentials.
Careful management of the secret keys shared between the client and the RADIUS server is another essential measure. The keys must be long, complex and unique for each pair of devices, as well as being regularly updated to minimize the risk of compromise. It is also important to avoid using default configurations, which often include weak passwords or inadequate security settings.
Finally, the administration of large networks should include the implementation of clear policies for the management of users and devices, using automation and monitoring tools to quickly detect and correct any configuration errors or attempted intrusions.
Regular auditing of the environment and ongoing training of IT teams are also essential to ensure that security best practices are followed and that the RADIUS protocol continues to provide an adequate level of protection on the network.
