Difference between revisions of "Preventing LDAP Injection in Java"

From OWASP
Jump to: navigation, search
m
(Reverting to last version not containing links to s1.shard.jp)
 
(23 intermediate revisions by 7 users not shown)
Line 1: Line 1:
Performing LDAP queries requires correctly escaping certain meta-characters. 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.  The examples below present Java methods that could be used to perform this escaping:
+
==Status==
 +
Needs to be reviewed
  
<em>Note: This is untested code</em>
+
==Approach==
  public String escapeDN (String name) {
+
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 [[:Category:OWASP Guide Project|the OWASP Development Guide]] about input validation.
         //From RFC 2253 and the / character for JNDI
+
 
        final char[] META_CHARS = {'+', '"', '<', '>', ';', '/'};
+
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.
        String escapedStr = new String(name);
+
 
        //Backslash is both a Java and an LDAP escape character, so escape it first
+
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.
         escapedStr = escapedStr.replaceAll("\\\\","\\\\");
+
 
        //Positional characters - see RFC 2253
+
    public static String escapeDN(String name) {
        escapedStr = escapedStr.replaceAll("^#","\\\\#");
+
         StringBuffer sb = new StringBuffer(); // If using JDK >= 1.5 consider using StringBuilder
        escapedStr = escapedStr.replaceAll("^ | $","\\\\ ");
+
         if ((name.length() > 0) && ((name.charAt(0) == ' ') || (name.charAt(0) == '#'))) {
        for (int i=0;i < META_CHARS.length;i++) {
+
             sb.append('\\'); // add the leading backslash if needed
             escapedStr = escapedStr.replaceAll("\\"+META_CHARS[i],"\\\\" + META_CHARS[i]);
+
 
         }
 
         }
         return escapedStr;
+
        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();
 
     }
 
     }
  
Note, that the backslash character is a Java String literal and a regular expression escape character.
+
Escaping the search filter:
      
+
 
  public String escapeSearchFilter (String filter) {
+
     public static final String escapeLDAPSearchFilter(String filter) {
         //From RFC 2254
+
         StringBuffer sb = new StringBuffer(); // If using JDK >= 1.5 consider using StringBuilder
         String escapedStr = new String(filter);
+
         for (int i = 0; i < filter.length(); i++) {
        escapedStr = escapedStr.replaceAll("\\\\","\\\\5c");
+
            char curChar = filter.charAt(i);
        escapedStr = escapedStr.replaceAll("\\*","\\\\2a");
+
            switch (curChar) {
        escapedStr = escapedStr.replaceAll("\\(","\\\\28");
+
                case '\\':
        escapedStr = escapedStr.replaceAll("\\)","\\\\29");
+
                    sb.append("\\5c");
         return escapedStr;
+
                    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"));
  
 
[[Category:OWASP Java Project]]
 
[[Category:OWASP Java Project]]

Latest revision as of 07:50, 3 June 2009

Status

Needs to be reviewed

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"));