1// Vulnerable Java LDAP authentication
2public boolean authenticate(String username, String password) {
3    // VULNERABLE: User input directly concatenated into LDAP filter
4    String filter = "(&(uid=" + username + ")(userPassword=" + password + "))";
5
6    SearchControls controls = new SearchControls();
7    controls.setSearchScope(SearchControls.SUBTREE_SCOPE);
8
9    NamingEnumeration<?> results = ctx.search(
10        "ou=users,dc=company,dc=com",
11        filter,
12        controls
13    );
14
15    return results.hasMore();
16}

1# Normal login:
2Username: jsmith
3Password: secret123
4Filter: (&(uid=jsmith)(userPassword=secret123))
5
6# Attack 1: Authentication bypass with wildcard
7Username: *
8Password: *
9Filter: (&(uid=*)(userPassword=*))
10→ Matches ANY user with ANY password — returns first user (often admin)
11
12# Attack 2: Authentication bypass with filter termination
13Username: admin)(|(&
14Password: anything)
15Filter: (&(uid=admin)(|(&)(userPassword=anything)))
16→ The injected (|(& creates an always-true condition
17
18# Attack 3: Bypass password check entirely
19Username: admin)(&)
20Password: anything
21Filter: (&(uid=admin)(&)(userPassword=anything))
22→ (&) is always true in many LDAP implementations

1# Log in as CEO without knowing password
2Username: ceo)(|(uid=*
3Password: anything)
4Filter: (&(uid=ceo)(|(uid=*)(userPassword=anything)))
5
6# This creates an OR condition that matches uid=* (everything)
7# Since LDAP returns the first match and uid=ceo is the first condition,
8# the LDAP server may return the CEO's account
9
10# Even simpler on some implementations:
11Username: ceo)(%00
12Password: anything
13Filter: (&(uid=ceo)(userPassword=anything))
14→ Null byte truncates the filter — password check is ignored

1# Example Active Directory hierarchy
2dc=company,dc=com                    ← Root (Domain Component)
3├── ou=Users                         ← Organizational Unit
4│   ├── cn=John Smith                ← Common Name (user entry)
5│   │   ├── uid=jsmith               ← User ID
6│   │   ├── mail=jsmith@company.com  ← Email
7│   │   ├── memberOf=cn=Admins,...   ← Group membership
8│   │   └── userPassword={SSHA}...   ← Hashed password
9│   ├── cn=Jane Doe
10│   └── cn=Bob Wilson
11├── ou=Groups
12│   ├── cn=Admins
13│   ├── cn=Developers
14│   └── cn=Finance
15├── ou=ServiceAccounts
16│   └── cn=ldap-reader
17└── ou=Computers
18    └── cn=WORKSTATION01

1# Every LDAP entry has a unique Distinguished Name (DN)
2# DNs are built from most-specific to least-specific (left to right)
3
4cn=John Smith,ou=Users,dc=company,dc=com    ← Full DN for a user
5cn=Admins,ou=Groups,dc=company,dc=com       ← Full DN for a group
6
7# DN components:
8# cn  = Common Name (leaf entry)
9# ou  = Organizational Unit (container)
10# dc  = Domain Component (domain)
11# uid = User ID (sometimes used instead of cn)
12# o   = Organization
13# c   = Country
14
15# DNs have their own special characters that must be escaped:
16# , + " \ < > ; = (space at start/end)

1# Simple equality filter
2(uid=jsmith)
3
4# AND filter — user must match all conditions
5(&(uid=jsmith)(objectClass=person)(!(disabled=TRUE)))
6
7# OR filter — user matches any condition
8(|(uid=jsmith)(mail=jsmith@company.com))
9
10# Wildcard / substring filters
11(cn=John*)         ← Starts with "John"
12(cn=*Smith)        ← Ends with "Smith"
13(cn=*admin*)       ← Contains "admin"
14
15# Nested logic
16(&(objectClass=person)(|(department=Engineering)(department=Security)))
17
18# Common authentication filter (the one most vulnerable to injection)
19(&(uid=USERNAME)(userPassword=PASSWORD))
20
21# Active Directory specific
22(&(sAMAccountName=USERNAME)(objectCategory=person)(objectClass=user))

1# Original filter template:
2(&(uid=USER)(userPassword=PASS))
3
4# Attacker input — username: admin)(|(uid=*
5# Resulting filter:
6(&(uid=admin)(|(uid=*)(userPassword=PASS)))
7
8# How LDAP evaluates this:
9# (&                              ← AND of two conditions
10#   (uid=admin)                   ← First: uid must be "admin"
11#   (|(uid=*)(userPassword=PASS)) ← Second: uid=* (always true) OR password check
12# )
13# Since uid=* is always true, the OR is always true
14# Only uid=admin needs to match → password is bypassed!

1// Vulnerable user search endpoint
2public List<User> searchUsers(String searchTerm) {
3    // VULNERABLE: Direct concatenation
4    String filter = "(cn=" + searchTerm + ")";
5
6    NamingEnumeration<?> results = ctx.search(
7        "ou=Users,dc=company,dc=com",
8        filter,
9        controls
10    );
11    // ...
12}
13
14// Normal use: searchTerm = "John" → (cn=John)
15// Attack:     searchTerm = "*"    → (cn=*) — returns ALL users!
16// Attack:     searchTerm = "a*"   → (cn=a*) — enumerate users starting with 'a'
17
18// More advanced enumeration:
19// searchTerm = "*)(uid=*"
20// Filter: (cn=*)(uid=*) — may return additional attributes

1# Original filter for a lookup endpoint:
2(uid=USER_INPUT)
3
4# Attack: Discover which users are admins
5# Input: *)(memberOf=cn=Admins,ou=Groups,dc=company,dc=com
6# Filter: (uid=*)(memberOf=cn=Admins,ou=Groups,dc=company,dc=com)
7# Returns all users who are in the Admins group
8
9# Attack: Find users with specific attributes
10# Input: *)(telephoneNumber=*
11# Filter: (uid=*)(telephoneNumber=*)
12# Returns all users who have a phone number set
13
14# Attack: Discover service accounts
15# Input: *)(objectClass=serviceAccount
16# Filter: (uid=*)(objectClass=serviceAccount)
17# Returns all service accounts in the directory

1# Some older LDAP implementations and language bindings
2# are vulnerable to null byte truncation
3
4# Original filter:
5(&(uid=USER)(userPassword=PASS))
6
7# Null byte injection — username: admin)%00
8# In some implementations, %00 terminates the string:
9(&(uid=admin)(userPassword=PASS))
10# Everything after the null byte is ignored
11# Effective filter: (&(uid=admin))
12# → Returns admin user without password check!
13
14# URL encoding variants:
15# admin)%00      → null byte via URL encoding
16# admin)     → null byte via hex encoding
17# admin)\00     → LDAP hex escape for null
18
19# NOTE: This mostly affects older Java LDAP, PHP ldap_search(),
20# and C-based LDAP libraries. Modern implementations are generally safe.

1// JNDI — The most common Java LDAP interface
2import javax.naming.directory.*;
3
4// CRITICAL SINKS:
5DirContext ctx = new InitialDirContext(env);
6
7// 1. search() with string filter — PRIMARY INJECTION VECTOR
8ctx.search("ou=Users,dc=com", filterString, searchControls);
9ctx.search(baseDN, filterString, filterArgs, searchControls);
10
11// 2. search() with SearchControls
12SearchControls sc = new SearchControls();
13sc.setSearchScope(SearchControls.SUBTREE_SCOPE);
14ctx.search(baseDNFromInput, filter, sc);  // Base DN injection too!
15
16// 3. lookup() and lookupLink()
17ctx.lookup("cn=" + userInput + ",ou=Users,dc=com");  // DN injection
18
19// 4. bind() — authentication
20ctx.addToEnvironment(Context.SECURITY_PRINCIPAL,
21    "cn=" + username + ",ou=Users,dc=com");  // DN injection
22ctx.addToEnvironment(Context.SECURITY_CREDENTIALS, password);
23
24// Spring LDAP
25LdapTemplate ldapTemplate;
26ldapTemplate.search(baseDN, filterString, mapper);   // Filter injection
27ldapTemplate.lookup(dnFromInput);                      // DN injection
28ldapTemplate.findOne(query, User.class);               // Check query source

1# python-ldap
2import ldap
3
4conn = ldap.initialize('ldap://server:389')
5
6# CRITICAL SINKS:
7# 1. search_s() / search_st() with filter string
8conn.search_s(
9    'ou=Users,dc=company,dc=com',   # Base DN (also injectable)
10    ldap.SCOPE_SUBTREE,
11    f'(uid={username})',              # VULNERABLE: f-string filter
12    ['cn', 'mail']                    # Attributes to return
13)
14
15# 2. search_ext_s() with filter
16conn.search_ext_s(base_dn, scope, filter_str)
17
18# 3. simple_bind_s() with DN from user input
19conn.simple_bind_s(
20    f'cn={username},ou=Users,dc=com',  # VULNERABLE DN
21    password
22)
23
24# 4. compare_s() with DN injection
25conn.compare_s(
26    f'cn={username},ou=Users,dc=com',  # VULNERABLE DN
27    'userPassword',
28    password
29)
30
31# ldap3 library
32from ldap3 import Connection, Server, ALL
33
34conn = Connection(server, user=user_dn, password=password)
35conn.search(
36    'ou=Users,dc=com',
37    f'(uid={user_input})',  # VULNERABLE filter
38    attributes=['cn', 'mail']
39)

1<?php
2// PHP has built-in LDAP extension functions
3
4// CRITICAL SINKS:
5// 1. ldap_search() — the primary injection vector
6$result = ldap_search(
7    $conn,
8    "ou=Users,dc=company,dc=com",
9    "(uid=" . $_POST['username'] . ")",  // VULNERABLE
10    ["cn", "mail"]
11);
12
13// 2. ldap_list() — single-level search
14$result = ldap_list($conn, $base_dn, $filter_from_input);
15
16// 3. ldap_read() — read specific entry
17$result = ldap_read($conn, $dn_from_input, "(objectClass=*)");
18
19// 4. ldap_bind() — authentication with DN injection
20$bind_dn = "cn=" . $_POST['username'] . ",ou=Users,dc=com";
21ldap_bind($conn, $bind_dn, $_POST['password']);
22
23// 5. ldap_compare() — attribute comparison
24ldap_compare($conn, $dn_from_input, "userPassword", $password);
25
26// NOTE: PHP does have ldap_escape() (since PHP 5.6)
27// but many codebases don't use it

1// System.DirectoryServices (Active Directory)
2using System.DirectoryServices;
3
4// CRITICAL SINKS:
5// 1. DirectorySearcher with filter string
6var searcher = new DirectorySearcher(entry);
7searcher.Filter = $"(&(sAMAccountName={username})(objectClass=user))";
8// VULNERABLE: filter built from user input
9var result = searcher.FindOne();
10
11// 2. DirectoryEntry path construction
12var entry = new DirectoryEntry(
13    $"LDAP://cn={username},ou=Users,dc=company,dc=com"  // DN injection
14);
15
16// 3. System.DirectoryServices.Protocols
17var searchRequest = new SearchRequest(
18    baseDn,
19    $"(uid={userInput})",  // VULNERABLE filter
20    SearchScope.Subtree,
21    attributeList
22);
23var response = (SearchResponse)connection.SendRequest(searchRequest);
24
25// 4. PrincipalSearcher (higher level, often safer)
26var ctx = new PrincipalContext(ContextType.Domain);
27var searcher = new PrincipalSearcher(
28    new UserPrincipal(ctx) { SamAccountName = userInput }
29);
30// Generally safer — but check if input reaches raw filter

1// Vulnerable: Building bind DN from user input
2public boolean authenticate(String username, String password) {
3    Hashtable<String, String> env = new Hashtable<>();
4    env.put(Context.INITIAL_CONTEXT_FACTORY, "com.sun.jndi.ldap.LdapCtxFactory");
5    env.put(Context.PROVIDER_URL, "ldap://ad.company.com:389");
6
7    // VULNERABLE: DN built from user input
8    String bindDN = "cn=" + username + ",ou=Users,dc=company,dc=com";
9    env.put(Context.SECURITY_PRINCIPAL, bindDN);
10    env.put(Context.SECURITY_CREDENTIALS, password);
11
12    try {
13        new InitialDirContext(env);  // Bind attempt
14        return true;
15    } catch (AuthenticationException e) {
16        return false;
17    }
18}
19
20// Attack: username = admin,ou=Users,dc=company,dc=com
21// Bind DN becomes: cn=admin,ou=Users,dc=company,dc=com,ou=Users,dc=company,dc=com
22// → Invalid DN, but some LDAP servers are lenient
23
24// More dangerous attack:
25// username = admin,ou=ServiceAccounts
26// Bind DN: cn=admin,ou=ServiceAccounts,ou=Users,dc=company,dc=com
27// → Attempts to bind as a service account instead of a user!

1# Vulnerable: User controls the base DN for search
2@app.route('/api/users/<department>')
3def get_department_users(department):
4    # VULNERABLE: Department name used in base DN
5    base_dn = f'ou={department},ou=Users,dc=company,dc=com'
6
7    result = conn.search_s(
8        base_dn,
9        ldap.SCOPE_SUBTREE,
10        '(objectClass=person)',
11        ['cn', 'mail', 'title']
12    )
13
14    return jsonify([entry for dn, entry in result])
15
16# Normal use: /api/users/Engineering
17# Base DN: ou=Engineering,ou=Users,dc=company,dc=com
18
19# Attack: /api/users/Engineering,dc=company,dc=com??sub?(objectClass=*)
20# May cause the search to start from a different location in the tree
21
22# Attack: /api/users/ServiceAccounts
23# Base DN: ou=ServiceAccounts,ou=Users,dc=company,dc=com
24# If ou=ServiceAccounts exists at this path, leaks service account info

1# DN has DIFFERENT special characters than LDAP filters
2# RFC 4514 specifies these must be escaped in DN values:
3
4,  (comma)      → \,   — Separates DN components
5+  (plus)       → \+   — Separates multi-valued RDN components
6"  (quote)      → \"   — Quoting character
7\  (backslash) → \\  — Escape character
8<  (less than)  → \<   — Distinguished encoding
9>  (greater)    → \>   — Distinguished encoding
10;  (semicolon)  → \;   — Alternative separator
11=  (equals)     → \=   — Attribute=value separator
12   (space at start/end) → \20  — Leading/trailing spaces
13
14# Example: Properly escaped DN value
15# Input: John "Admin" Smith, Jr.
16# Escaped: cn=John \"Admin\" Smith\, Jr.,ou=Users,dc=com

1// Java — Use JNDI's built-in filter escaping
2import javax.naming.directory.*;
3
4// SAFE: Use search() with filter arguments (parameterized!)
5String filter = "(&(uid={0})(userPassword={1}))";
6Object[] filterArgs = { username, password };
7
8ctx.search("ou=Users,dc=company,dc=com", filter, filterArgs, controls);
9// JNDI escapes metacharacters in {0}, {1} automatically!
10// This is the Java equivalent of parameterized SQL queries.
11
12// Alternative: Manual escaping function
13public static String escapeFilterValue(String value) {
14    StringBuilder sb = new StringBuilder();
15    for (char c : value.toCharArray()) {
16        switch (c) {
17            case '*':  sb.append("\\2a"); break;
18            case '(':  sb.append("\\28"); break;
19            case ')':  sb.append("\\29"); break;
20            case '\\': sb.append("\\5c"); break;
21            case '\0': sb.append("\\00"); break;
22            default:   sb.append(c);
23        }
24    }
25    return sb.toString();
26}
27
28// Usage:
29String safeFilter = "(&(uid=" + escapeFilterValue(username) + ")" +
30                     "(userPassword=" + escapeFilterValue(password) + "))";

1// Spring LDAP provides built-in filter encoding
2import org.springframework.ldap.filter.*;
3import org.springframework.ldap.support.LdapEncoder;
4
5// SAFE: Use Spring's filter builder classes
6AndFilter filter = new AndFilter();
7filter.and(new EqualsFilter("uid", username));      // Auto-escaped
8filter.and(new EqualsFilter("userPassword", password)); // Auto-escaped
9
10ldapTemplate.search("ou=Users", filter.encode(), mapper);
11
12// SAFE: LdapEncoder for manual escaping
13String safeValue = LdapEncoder.filterEncode(userInput);
14String safeFilter = "(uid=" + safeValue + ")";
15
16// SAFE: DN encoding
17String safeDN = LdapEncoder.nameEncode(userInput);
18String dn = "cn=" + safeDN + ",ou=Users,dc=company,dc=com";
19
20// SAFE: Use LdapQueryBuilder (Spring LDAP 2.x+)
21LdapQuery query = LdapQueryBuilder.query()
22    .base("ou=Users")
23    .where("uid").is(username)  // Automatically escaped
24    .and("objectClass").is("person");
25
26ldapTemplate.search(query, mapper);

1# python-ldap — Use ldap.filter.escape_filter_chars()
2import ldap
3from ldap.filter import escape_filter_chars
4from ldap.dn import escape_dn_chars
5
6# SAFE: Escape filter values
7safe_username = escape_filter_chars(username)
8filter_str = f'(uid={safe_username})'
9
10conn.search_s('ou=Users,dc=com', ldap.SCOPE_SUBTREE, filter_str)
11
12# SAFE: Escape DN values
13safe_cn = escape_dn_chars(username)
14bind_dn = f'cn={safe_cn},ou=Users,dc=company,dc=com'
15
16conn.simple_bind_s(bind_dn, password)
17
18# ldap3 library — Built-in escaping
19from ldap3.utils.conv import escape_filter_chars as l3_escape
20
21safe_input = l3_escape(user_input)
22conn.search('ou=Users,dc=com', f'(uid={safe_input})', attributes=['cn'])
23
24# Custom validation + escaping
25import re
26
27def validate_username(username: str) -> str:
28    """Validate and sanitize username for LDAP queries."""
29    if not isinstance(username, str):
30        raise ValueError('Username must be a string')
31    if not re.match(r'^[a-zA-Z0-9._-]+$', username):
32        raise ValueError('Username contains invalid characters')
33    return escape_filter_chars(username)

1<?php
2// PHP 5.6+ — Use ldap_escape()
3
4// SAFE: Escape for filter context
5$safe_username = ldap_escape($username, '', LDAP_ESCAPE_FILTER);
6$filter = "(uid=$safe_username)";
7$result = ldap_search($conn, $base_dn, $filter);
8
9// SAFE: Escape for DN context (different special chars!)
10$safe_cn = ldap_escape($username, '', LDAP_ESCAPE_DN);
11$bind_dn = "cn=$safe_cn,ou=Users,dc=company,dc=com";
12ldap_bind($conn, $bind_dn, $password);
13
14// IMPORTANT: Use the correct flag!
15// LDAP_ESCAPE_FILTER — escapes *, (, ), \, NUL
16// LDAP_ESCAPE_DN     — escapes ,, +, ", \, <, >, ;, =, spaces
17// Using the wrong one leaves the application vulnerable!
18
19// Input validation before escaping (belt + suspenders)
20function validateUsername(string $username): string {
21    if (!preg_match('/^[a-zA-Z0-9._-]+$/', $username)) {
22        throw new InvalidArgumentException('Invalid username');
23    }
24    return ldap_escape($username, '', LDAP_ESCAPE_FILTER);
25}

1// .NET — No built-in LDAP escaping until .NET 8!
2// You must implement your own or use a library
3
4// Custom filter escaping (RFC 4515)
5public static string EscapeLdapFilterValue(string value)
6{
7    var sb = new StringBuilder();
8    foreach (char c in value)
9    {
10        switch (c)
11        {
12            case '*':  sb.Append("\2a"); break;
13            case '(':  sb.Append("\28"); break;
14            case ')':  sb.Append("\29"); break;
15            case '\': sb.Append("\5c"); break;
16            case '': sb.Append("\00"); break;
17            default:   sb.Append(c); break;
18        }
19    }
20    return sb.ToString();
21}
22
23// SAFE usage:
24var safeUser = EscapeLdapFilterValue(username);
25searcher.Filter = $"(&(sAMAccountName={safeUser})(objectClass=user))";
26
27// SAFER: Use PrincipalSearcher for Active Directory (avoids raw filters)
28using (var ctx = new PrincipalContext(ContextType.Domain))
29using (var principal = new UserPrincipal(ctx))
30{
31    principal.SamAccountName = username;  // Handled safely by framework
32    using (var searcher = new PrincipalSearcher(principal))
33    {
34        var result = searcher.FindOne();
35    }
36}