Sophia Sophia - 15 days ago 11
C# Question

How to escape a string in C#, for use in an LDAP query

I have an LDAP query, which I am using to perform a search in C#. It uses two string variables (username and domain) which need to be escaped for security reasons.

How should I escape the strings? Is there a function available in C#.NET to do this?




Example LDAP search conditions :

(objectCategory=person)
(userprincipalname=username@domain*)
(samaccountname=username)


Example LDAP query string in C# :

string search = "(&(&(objectCategory=person)(userprincipalname="
+ username
+ "@"
+ domain
+ "*)(samaccountname="
+ username
+ ")))";


Edit: I already have the LDAP query working, and returning results. All I want is to escape the parameters.

Answer

The following is my translation from the Java code mentioned by Sophia into C#.

/// <summary>
/// Escapes the LDAP search filter to prevent LDAP injection attacks.
/// </summary>
/// <param name="searchFilter">The search filter.</param>
/// <see cref="https://blogs.oracle.com/shankar/entry/what_is_ldap_injection" />
/// <see cref="http://msdn.microsoft.com/en-us/library/aa746475.aspx" />
/// <returns>The escaped search filter.</returns>
private static string EscapeLdapSearchFilter(string searchFilter)
{
    StringBuilder escape = new StringBuilder(); // If using JDK >= 1.5 consider using StringBuilder
    for (int i = 0; i < searchFilter.Length; ++i)
    {
        char current = searchFilter[i];
        switch (current)
        {
            case '\\':
                escape.Append(@"\5c");
                break;
            case '*':
                escape.Append(@"\2a");
                break;
            case '(':
                escape.Append(@"\28");
                break;
            case ')':
                escape.Append(@"\29");
                break;
            case '\u0000':
                escape.Append(@"\00");
                break;
            case '/':
                escape.Append(@"\2f");
                break;
            default:
                escape.Append(current);
                break;
        }
    }

    return escape.ToString();
}