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A whitelist can be used to restrict input to a list of valid characters. Characters and character sequences that must be excluded from whitelists—including Java Naming and Directory Interface (JNDI) metacharacters and LDAP special characters—are listed in the following table.

Characters and Sequences to Exclude from Whitelists

Character	Name
`'` and `"`	Single and double quote
`/` and `\`	Forward slash and backslash
`\\`	Double slashes*
space	Space character at beginning or end of string
`#`	Hash character at the beginning of the string
`<` and `>`	Angle brackets
`,` and `;`	Comma and semicolon
`+` and `*`	Addition and multiplication operators
`(` and `)`	Round braces
`\u0000`	Unicode `NULL` character

* This is a character sequence.

LDAP Injection Example

Consider an LDAP Data Interchange Format (LDIF) file that contains records in the following format:

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An authentication routine that permitted LDAP injection would allow unauthorized users to log in. Likewise, a search routine would allow an attacker to discover part or all of the data in the directory.

Noncompliant Code Example

This noncompliant code example allows a caller of the method searchRecord() to search for a record in the directory using the LDAP protocol. The string filter is used to filter the result set for those entries that match a user name and password supplied by the caller.

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When a malicious user enters specially crafted input, as outlined previously, this elementary authentication scheme fails to confine the output of the search query to the information for which the user has access privileges.

Compliant Solution

This compliant solution uses a whitelist to sanitize user input so that the filter string contains only valid characters. In this code, userSN may contain only letters and spaces, whereas a password may contain only alphanumeric characters.

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When a database field such as a password must include special characters, it is critical to ensure that the authentic data is stored in sanitized form in the database and also that any user input is normalized before the validation or comparison takes place. Using characters that have special meanings in JNDI and LDAP in the absence of a comprehensive normalization and whitelisting-based routine is discouraged. Refer to 06. Properly encode or escape output for examples of output encoding and escaping. Special characters must be transformed to sanitized, safe values before they are added to the whitelist expression against which input will be validated. Likewise, normalization of user input (escaping and encoding) should occur before the validation step.