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Identity systems play an important role in managing user access, and attackers often look for ways to exploit how applications interact with them. Lightweight directory access protocol (LDAP) injection is one of these paths. It targets the queries sent to an LDAP server and, if mishandled, can lead to unauthorized access or exposure to sensitive data.
Any application that uses LDAP for login or directory lookups can be a target. Here’s a guide to LDAP injection, the most common attack types, and how to prevent them.
What Is an LDAP Injection?
LDAP queries and manages directory services like Microsoft Active Directory or OpenLDAP. When an application needs to authenticate a user or look up account information, it sends an LDAP query to the directory server. These directories store and organize data about user and device permissions. Along with powering login systems, access controls, and organizational hierarchies, they’re often integral to identity-driven systems used in application risk assessments.
LDAP attacks take advantage of this query process. Attackers insert user input into an LDAP query to alter its behavior during these attacks. If the application doesn’t sanitize that input, attackers can inject special characters or malicious code to manipulate the query and force unintended behavior. This attack can lead to unauthorized access, data exposure, or even changes to the directory itself.
How Does an LDAP Injection Work?
LDAP injection inserts malicious input into a user-facing field, like a login form or search box. The application passes that input into an LDAP query, allowing the attacker to change what the query returns or who it grants access to. This makes it a key concern during application security testing.
It’s similar to SQL injection in that both target applications that build queries with user-supplied data. The key difference is the target—LDAP attacks directory services like Active Directory, while SQL injection targets databases.
Here's an example of LDAP injection and how it might work. Let’s say a login form asks for a username and password. Behind the scenes, the application builds an LDAP query that looks for a user object matching both values.
But if the app doesn’t validate the input, an attacker could submit something like admin)(|(memberOf=*)) as the username. That input breaks out of the expected structure and adds a condition that always evaluates as true, allowing the attacker to modify how the query functions. Without the correct password, the query may return the admin account—or any account with group memberships.
Types of LDAP Injection Attacks
LDAP injection doesn’t always look the same. Below are several common LDAP injection attack types and how they impact systems:
Access Control Bypass
Access control bypass is one of the most common outcomes of LDAP injection. Attackers inject conditions that always return true when developers build login filters with unsanitized input, completely bypassing password checks. These LDAP injection vulnerabilities often surface during an application risk assessment, especially when authentication depends on directory-based identity.
Resource Disclosure
Applications often use LDAP searches to look up internal resources like users, systems, or objects by filtering specific attributes or values from the directory. When developers include user input in filters without proper validation, attackers can craft inputs to list every object of that type. Organizations that follow a structured application security risk assessment checklist are more likely to catch these LDAP vulnerabilities before attackers expose them in production.
Elevation of Privileges
LDAP filters frequently control user access based on group membership or roles. Attackers can manipulate a poorly constructed filter to include privileged objects, even if the user cannot access them. Catching these vulnerabilities early depends on maintaining a strong vulnerability management lifecycle, not just patching obvious bugs.
Blind LDAP Injection
Even when the application doesn’t return detailed error messages, attackers can still learn from its behavior. Blind injection sends inputs that produce a true or false response, allowing attackers to slowly map the directory structure or test for specific users and attributes. These attacks often slip past standard checks but become visible when you model more advanced threat scenarios.
Preventing LDAP Injection Attacks: 6 Tips
Preventing LDAP injection starts with controlling user input and building multiple safeguards to block attacks and limit the fallout. Here’s how to tighten your defenses:
1. Sanitize Inputs
Untrusted input is the root of most LDAP injection issues. Sanitize input before it reaches a query to strip or escape special characters like *, &, |, =, and !. These characters have meaning in LDAP filters, and if you don’t handle filters properly, attackers can manipulate query logic.
Avoid relying on client-side validation alone. All input sanitization should happen server-side, using purpose-built LDAP encoding functions for search filters and distinguished names (DNs).
2. Implement Access Control on the LDAP Server
Even if an attacker gets a malicious query through, strict LDAP permissions reduce what they can access. The application’s LDAP account should only have read access to what it needs and nothing more.
A least-privilege model—also known as the principle of least privilege—limits the scope of exposure even when attackers abuse queries. For added security, consider separating search accounts from write-enabled ones and using proxied authentication when needed.
3. Use Frameworks
Building queries manually through string concatenation is risky. Frameworks and libraries that offer parameterized LDAP filters help you avoid injecting user input directly into query strings. These tools structure the query logic to prevent injection naturally.
If your stack doesn’t support parameterized filters, explore switching libraries or introducing a layer that escapes input before it reaches LDAP logic.
4. Use Allowlists and Validation
Sanitization is only one side of the input puzzle. Strong input validation is the other. Instead of trying to block dangerous input, identify what good input looks like. For example, use allowlists to restrict usernames to alphanumeric characters or specific formats and reject anything else outright.
This step is especially important when handling structured inputs like email addresses or directory IDs, where attackers frequently attempt to slip in metacharacters.
5. Restrict LDAP Query Scope and Behavior
Beyond input controls, limit what your LDAP server will allow in a query. Set base DNs that restrict searches to specific parts of the directory, define search scopes tightly, and apply size and time limits to prevent data overexposure or long-running brute-force attempts. These controls form a second line of defense that limits what well-formed injection attacks can access.
6. Test for LDAP Injection Vulnerabilities Early
Don’t wait until production to find injection flaws. During development, use dynamic application security testing (DAST) tools or fuzzing techniques to trigger and detect unsafe LDAP behaviors. By incorporating LDAP-focused testing into your vulnerability management best practices, you can catch these flaws before they reach production. The earlier you catch these vulnerabilities in the development lifecycle, the less costly and risky they become.
Defend Against LDAP Injection Attacks With Legit Security
Preventing LDAP injection requires more than basic sanitization. You need strong validation, secure query construction, and a way to consistently apply those standards across development. That’s especially important in fast-moving environments where changes happen quickly and misconfigurations can slip through.
Legit Security helps you detect LDAP injection vulnerabilities early before they become real risks. It integrates into your existing workflows and provides visibility into how your application builds and uses LDAP queries. Request a demo today.