Preventing LDAP Injection in Java

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Last revision (yyyy-mm-dd): 2008-03-01
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Approach

The best way to prevent LDAP injection is to use a positive validation scheme for ensuring that the data going into your queries doesn't contain any attacks. You can read more in the OWASP Development Guide about input validation.

However, in some cases, it is necessary to include special characters in input that is passed into an LDAP query. In this case, using escaping can prevent the LDAP interpreter from thinking those special characters are actually LDAP query. Rather, the encoding lets the interpreter treat those special characters as data.

Here are a few methods for escaping certain meta-characters in LDAP queries. Both the distinguished name (DN) and the search filter have their own sets of meta-characters. In the case of Java, it is also necessary to escape any JNDI meta-characters, since java uses JNDI to perform LDAP queries.

   public static String escapeDN(String name) {
       StringBuffer sb = new StringBuffer(); // If using JDK >= 1.5 consider using StringBuilder
       if ((name.length() > 0) && ((name.charAt(0) == ' ') || (name.charAt(0) == '#'))) {
           sb.append('\\'); // add the leading backslash if needed
       }
       for (int i = 0; i < name.length(); i++) {
           char curChar = name.charAt(i);
           switch (curChar) {
               case '\\':
                   sb.append("\\\\");
                   break;
               case ',':
                   sb.append("\\,");
                   break;
               case '+':
                   sb.append("\\+");
                   break;
               case '"':
                   sb.append("\\\"");
                   break;
               case '<':
                   sb.append("\\<");
                   break;
               case '>':
                   sb.append("\\>");
                   break;
               case ';':
                   sb.append("\\;");
                   break;
               default:
                   sb.append(curChar);
           }
       }
       if ((name.length() > 1) && (name.charAt(name.length() - 1) == ' ')) {
           sb.insert(sb.length() - 1, '\\'); // add the trailing backslash if needed
       }
       return sb.toString();
   }

Escaping the search filter:

   public static final String escapeLDAPSearchFilter(String filter) {
       StringBuffer sb = new StringBuffer(); // If using JDK >= 1.5 consider using StringBuilder
       for (int i = 0; i < filter.length(); i++) {
           char curChar = filter.charAt(i);
           switch (curChar) {
               case '\\':
                   sb.append("\\5c");
                   break;
               case '*':
                   sb.append("\\2a");
                   break;
               case '(':
                   sb.append("\\28");
                   break;
               case ')':
                   sb.append("\\29");
                   break;
               case '\u0000': 
                   sb.append("\\00"); 
                   break;
               default:
                   sb.append(curChar);
           }
       }
       return sb.toString();
   }

Test class:

       //escapeDN
       assertEquals("No special characters to escape", "Helloé", escapeDN("Helloé"));
       assertEquals("leading #", "\\# Helloé", escapeDN("# Helloé"));
       assertEquals("leading space", "\\ Helloé", escapeDN(" Helloé"));
       assertEquals("trailing space", "Helloé\\ ", escapeDN("Helloé "));
       assertEquals("only 3 spaces", "\\  \\ ", escapeDN("   "));
       assertEquals("Christmas Tree DN", "\\ Hello\\\\ \\+ \\, \\\"World\\\" \\;\\ ", Test.escapeDN(" Hello\\ + , \"World\" ; "));

       assertEquals("No special characters to escape", "Hi This is a test #çà", SecTool.escapeLDAPSearchFilter("Hi This is a test #çà"));
       assertEquals("LDAP Christams Tree", "Hi \\28This\\29 = is \\2a a \\5c test # ç à ô", SecTool.escapeLDAPSearchFilter("Hi (This) = is * a \\ test # ç à ô"));