In the complex world of cybersecurity, there are myriad types of threats to be aware of, especially regarding application vulnerabilities. Injection attacks are some of the most popular attacks you may have to deal with, and an LDAP injection is one of them.
In a nutshell, with an LDAP injection attack, a malicious user exploits a security loophole caused by unsanitized user-supplied input to inject commands and eventually gain access to secure data. This type of input validation vulnerability can lead to detrimental effects for the targeted server, exposing it fully for manipulation.
What Is Lightweight Directory Access Protocol?
LDAP stands for ‘Lightweight Directory Access Protocol.’ It’s a popular software protocol used to locate resources, including files, devices, and individuals. For example, intranets often employ directory services like LDAP. This protocol can also serve as a storage place for authentication credentials like usernames and passwords within single sign-on (SSO) systems.
Importance of LDAP Servers
LDAP servers are commonly used. The protocol provides a popular form of the authentication flow.
What is LDAP authentication? In essence, it is a widely used authentication process. Websites that employ LDAP through LDAP directories that collect information as objects. The most used way for authenticating LDAP clients is the simple bind authentication. The client creates an anonymous bind using an empty distinguished name (DN).
An attacker can inject malicious code in the form of user-controllable input. This is how they can get access to stored credentials and modify them.
What Are LDAP Injections?
LDAP injections are one of many code injection techniques. They are a relatively common security risk due to the frequent use of LDAP authentication mechanisms and the vulnerability of LDAP query interfaces.
How Does an LDAP Injection Vulnerability Work?
LDAP injection attacks can be executed by malicious users when web-based applications don’t check user input rigorously and thus create a loophole for unauthorized LDAP statements modifications.
Similar to an SQL injection, LDAP injection attacks happen when an attacker exploits this security fault that allows unsanitized input with the help of a local proxy. As a result, they can obtain permissions and execute malicious commands for unauthorized queries or modify content within the LDAP tree.
More specifically, attackers can control the meaning of a query through the use of metacharacters like brackets, asterisks, ampersands, and quotes. If they can submit such input, they can change the query in an unauthorized way to achieve their goal. The newly passed parameters can manipulate the search, addition, and modification functions.
The injection flaws in the case of LDAP are a significant security threat. If successfully executed, they can provide attackers with sensitive data, such as credentials, roles, permissions, and more. Furthermore, this attack often results in authentication bypasses, data corruption, or denial of service (DoS), ruining the attacked server.
Types of LDAP Injections
There are two main types of LDAP injections — the classical one and the BLIND variation. The former has been described above, while the latter is detailed in the following section.
In addition, every LDAP injection can be one of two kinds, depending on the logical operators: AND (using the ‘&’ operator) or OR (using the ‘I’ operator). This is applicable for both classical and BLIND LDAP injection attacks.
BLIND LDAP Injection
The BLIND LDAP injection attack is a particular type of LDAP attack. It takes more time to put it into action than the regular one. However, because it is based on binary logic, the BLIND injection techniques are relatively easy to execute, so they can also be seen as an advanced LDAP injection.
The BLIND injection attack exploits the possibility to infer information from server responses based on Boolean logic. Even though the web application does not exhibit error messages, an attacker can inject code in the LDAP filter that creates a valid response or an error — meaning either a true or false result. The malicious user can use this to direct true or false response types of questions to the server and can thus ultimately obtain sensitive data.
How to Prevent an LDAP Injection Attack?
While LDAP injection attacks are common, this doesn’t mean you can’t take steps to stop them from affecting your systems. Protection against LDAP injection is not complicated. In essence, the essential measure is to ensure that input sanitization is correctly executed so that the insertion of special characters is prevented and thus the exertion of malicious commands.
There are two main ways to do that which security experts have recommended:
- Use the appropriate LDAP encoding function to escape all variables
- Employ a framework that takes care of escaping automatically
In the first case, you have to escape all untrusted inputs from adding to an LDAP query. Then, you have to choose between LDAP Search and LDAP DN (distinguished name) escaping, depending on the particularities of your systems.
In the second option, you can use a framework like LINQtoAD. It creates automatic LDAP encoding for LDAP queries.
In all cases, it’s also recommended to use additional defenses. The extra layer of protection measures can include:
- The primary defense is to minimize the privileges (Least Privilege) given to the LDAP binding account. Even if there are successful code injection attacks, that’s how you can limit the impact.
- Configure proper input validation (Allow-List input validation). If unauthorized input is sent to the LDAP query, it can detect it.
In addition, you can consult OWASP’s LDAP Injection Prevention Cheat Sheet for a complete overview of the protection methods.
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