Custom Neutralizations

The root cause of many security breaches is trusting invalidated input. This could be:

• Input from the user, which could be considered as tainted (possibly controlled by an adversary), i.e user is considered an untrusted source
• Data, assuming it is untainted (must not be controlled by an adversary), i.e., sensitive data sinks rely on trusted (untainted) data

The goal of Tainted Flow Analysis is to detect tainted data flows:

Prove, for all possible sinks, that tainted data will never be used where untainted data is expected. 

When inferring flows from an untainted sink to a tainted source, Kiuwan can detect if any well-known sanitizer is used, dropping those flows and thus avoiding raising false vulnerabilities.

Kiuwan contains a built-in library of sanitizers for every supported programming language and framework.

These sanitizers are commonly used directly by programmers or by frameworks. And Kiuwan detects their use.

Further reading: Read more here Understanding Data-Flow Vulnerabilities.

Data Neutralization Model

Complex subsystems that accept string data that may hold commands or instructions need neutralization of inputs targeted to them.

If untrusted input enters the subsystem may result in the unexpected execution of commands/actions, and an injection security flaw exists. Examples of such subsystems that are candidates for injection attacks are:

• The operating system command interpreter   
• Data repository with the SQL engine
• XML parser
• XPath / XQuery evaluator
• LDAP directory service API
• Script engines
• Regexp compilers (e.g. the pcre_replace() PHP function with /e pattern modifier)

 The first defense line against application attacks is adequate input validation.

• Should be positive, “accept only which is known to be good” (whitelist), not negative, “reject what is known to be bad” (blacklist).
• Sometimes output escaping is a good thing (e.g. against XSS; but less against SQLi and other attacks)

• Canonicalization / Normalization
  • Canonicalization is the process of lossless reduction of input to its equivalent simplest known form (for example, replacing .. and . in a pathname to produce canonicalized pathname, Unicode canonical equivalence…).
  • Normalization is the process of lossy conversión of input data to the simplest form (e.g. converting a text input into one value from a fixed set, removing accents, removing whitespace, stop words and punctuation chars, lower-/upper-casing…).
• Sanitization
  • Ensuring that data conforms to the requirements of the subsystem to which it is passed, including security requirements related to data leakage or sensitive data exposure across the trust boundary. This may include the removal of unwanted characters, escaping metacharacters, etc.
• Validation
  • Ensuring that input falls within the expected domain of valid program input: type/numeric range requirements, input invariants…

Kiuwan contains a built-in library of sanitizers for every supported programming language and framework. These sanitizers are commonly used directly by programmers or by frameworks. And Kiuwan detects their usage.

But if you are using your sanitizers, Kiuwan could not recognize them as such, detecting false “tainted data flow”.  In this case, you should let Kiuwan be aware of them.

The goal of this section is to teach you how to incorporate custom sanitizers to the Kiuwan built-in library.

During the next section, we will use the terms “sanitizers” and “neutralization routines” as synonyms.
 

Neutralization Routines (a.k.a Sanitizers)

This documentation is not related to how to build custom neutralization routines but how to add your custom neutralization routines to Kiuwan.

The process consists of:

• First, let Kiuwan know your routine
  • Depending on the programming language you are analyzing, the so-called “routine” can be a function, a method of a class, etc.
• Second, let Kiuwan know that it’s a neutralization
  • Kiuwan provides some ways to define your routine (we will see it later), but regardless of it, you need to indicate that routine as “neutralization”.

Next, for instruction purposes, we will follow these steps using Java as the programming language. Differences with other programming languages will be further detailed.
 

Specifying custom neutralization routines

Locations and precedence

Neutralization routines can be configured at different scopes

• Single-analysis,
• Application-specific and
• System-wide.

Depending on the location of the XML file, precedence and scope will change.

Precedence and scope of configurations are as follows:

• Single-Analysis
  • Neutralizations can apply only to a unique analysis.
  • In this case, the XML file should be located at:

    • [analysis_base_dir]/libraries/[technology]

• Application-specific
  • Neutralizations can apply to all analyses of a specific application.
  • In this case, the XML file should be located at:

    • [agent_home_dir]/conf/apps/[app_name]/libraries/[technology] 

• System-wide
  • Neutralizations can apply to all analyses of all applications.
  • In this case, the XML file should be located at:

    • [agent_home_dir]/conf/libraries/[technology] 

  • Exceptions to this rule are:
    • CPP engine reads from  …/libraries/c
    • objective engine reads from …/libraries/objetivec and …/libraries/c

Hint: As a general recommendation, we suggest naming the XML file as [technology]_custom_neutralizations.xml (this will help to identify your custom files from Kiuwan's files).

Therefore, the next sections will use java_custom_neutralizations.xml as the name for our custom file.
 

Creating a custom “Library” of neutralization routines

You don’t need to create an XML file for every single neutralization routine.

Instead, you will include all of them in a single file identified as a library of custom neutralization routines, with a name for it.

Library identification will be an XML element such as:

<library name="java.custom.libraries"/>

As a suggestion, we recommend using something like: [technology].custom.library

Please refer to the schema file for editing custom libraries of neutralization routines.

As said above, a Neutralization Routine is a piece of code that assures that any tainted data got as input produces untainted data as output.

That piece of code is typically a function or a class method (depending on whether your technology is object-oriented or not).

To declare the routine, you must include the element. The schema file describes the allowed set of elements that form part of the library.

For our purposes, commonly used elements are either class or function, depending on the language. 

Once, the routine is declared, it must be marked as a neutralization routine as follows. See the reference section for more details on how to declare a routine.
 

Examples

Let’s see some explained examples of custom neutralizations:

Example 1 (Java)

Note: The reference to optimyth.com is only a namespace, not an actual web-hosted file. Optimyth is a name previously used for Kiuwan.

In this example, the method validate is a custom neutralization for a path from a source to a path traversal sink. The input of method validate is neutralized, and the output (referred by argpos -1 in the neutralization definition in the XML library), is untainted after the validation is executed.

The next source code shows an example of how to use the neutralization:

package com.mycompany.onepackage;

import com.mycompany.otherpackage.MyUtils;
import javax.servlet.http.HttpServletRequest ;
import java.io.FileInputStream;
public class MyClass {
   // ...
   public void methodThatAccessToFileSystem(HttpServletRequest req) {
       String inputFile = req.getParameter("file"); //inputFile tainted
       inputFile = MyUtils.validate(inputFile + ".tmp"); //inputFile untainted after validation
       return new FileInputStream(SAFE_DIR.getAbsoluteFile() + inputFile);
   }
   // ...
}

=======================================

  
package com.mycompany.otherpackage;

import com.mycompany.IMyUtilsClass; 

public class MyUtils implements IMyUtilsClass {
    // ....
    public String validate(String value) {
        // ...
        // perform string value validation/Canonicalization/Normalization/Sanitization
        // ...
        return value; // once cleaned up
    }
}

<?xml version="1.0" encoding="UTF-8"?>
<library xmlns="http://www.optimyth.com/schema/definitions/library_metadata"xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
name="java.custom.libraries" standard="custom" technology="java">
<class name="com.mycompany.otherpackage.MyUtils" kind="class" supertypes="com.mycompany.IMyUtilsClass">
<method name="validate" signature="validate(java.lang.String)" match="name">
<return type="java.lang.String"/>
<neutralization argpos="-1" kind="path_traversal" resource="web" />
</method>
</class>
</library>

Example 2 (Java)

Note: The reference to optimyth.com is only a namespace, not an actual web-hosted file. Optimyth is a name previously used for Kiuwan.

In the following example the neutralization only affects filesystem resources:

package com.mycompany.onepackage;

import com.mycompany.otherpackage.CustomFile;
import javax.servlet.http.HttpServletRequest;
import java.io.FileInputStream;
public class MyClass {
// ...
public void methodThatAccessToFileSystem(HttpServletRequest req) {
String inputFile = req.getParameter("file"); //inputFile tainted
CustomFile file = new CustomFile(inputFile);
file.sanitize(); //file untainted after sanitization
return new FileInputStream(SAFE_DIR.getAbsoluteFile() + file);
}
}

=====================================

package com.mycompany.otherpackage;

import java.io.File;

public class CustomFile extends File {
//..
public void sanitize() {
// perform file sanitization
}
}

Neutralization declaration in the library XML file:

<?xml version="1.0" encoding="UTF-8"?>
<library xmlns="http://www.optimyth.com/schema/definitions/library_metadata"xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"name="java.custom.libraries" standard="custom" technology="java">
<class name="com.mycompany.otherpackage.CustomFile" kind="class" supertypes="java.io.File">
<method name="sanitize" signature="sanitize()">
<neutralization argpos="-2" kind="string" resource="filesystem"/>
</method>
</class>
</library>

Example 3 (Java)

Note: The reference to optimyth.com is only a namespace, not an actual web-hosted file. Optimyth is a name previously used for Kiuwan.

In this example, a Java annotation is used as neutralization.

package com.mycompany.onepackage;

import java.sql.ResultSet;
import java.sql.Statement;
import java.sql.Connection;

public class Main {

private Connection con;

public static void main(String[] args) {
String name = args[0];
Item item = new Item(name);
process(item);
}
public static void process(Item item) {
try {
ResultSet rs = null;
Statement stmt = con.createStatement();
String input = item.getName();
rs=stmt.executeQuery("select * from items where item_name="+ input);    // input is tainted
} catch (...) {
// ...
}
}
}

=====================================

package com.mycompany.onepackage;


import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;


@Target({ElementType.FIELD, ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
public @interface MyAnnotation {
// perform neutralization
}


=====================================


package com.mycompany.onepackage;


public class Item {
String name;


public Item(String name) {
super();
this.name = name;
}


@MyAnnotation()
public String getName() {
return name;
}


public void setName(String name) {
this.name = name;
}
}

So, you should declare the annotation as neutralization in the library XML file as:

<?xml version="1.0" encoding="UTF-8"?>
<library xmlns="http://www.optimyth.com/schema/definitions/library_metadata"xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
name="java.custom.libraries" standard="custom" technology="java">
<annotation name="com.mycompany.onepackage.MyAnnotation">
<neutralization kind="sql_injection" />
</annotation>
</library>

Neutralization elements

A neutralization identifies an element (essentially a method call) as a vulnerability neutralizer. It is defined in Kiuwan by the following element:

<!ELEMENT neutralization (#PCDATA)*>
<!ATTLIST neutralization
argpos CDATA #REQUIRED
kind CDATA #IMPLIED
resource %resource; #IMPLIED
>

• rgpos

  The argpos attribute specifies what object (or objects) are untainted by the routine. It indicates which element is being neutralized by this neutralization. Depending on how your custom neutralization routine works, you should code a different value in this argument. Allowed values are:

  0..n: A non-negative value indicates that the argument at the given index (starting at 0)is being neutralized.   obj.call(arg1, arg2) arg1 is neutralized when argpos="0" arg2 is neutralized when argpos="1" Both are neutralized when argpos="0,1"	<method name="call" signature="call(fqcn.Arg1Type, fqcn.Arg2Type)"> <neutralization argpos="0" kind="..." resource="..." /> </method>
  -1: Target object (returned value) is being neutralized.   value = obj.call(arg1) value is neutralized when argpos="-1"	<method name="call" signature="call(fqcn.Arg1Type)"> <return type="fqcn.ValueType"/> <neutralization argpos="-1" kind="..." resource="..." /> </method>
  -2: Called object is being neutralized. obj.call() obj is neutralized when argpos="-2"	<method name="call" signature="call()"> <neutralization argpos="-2" kind="..." resource="..." /> </method> Neutralization routines could be defined in the same class where they are used, or in a different one, where you can invoke them through an object instantiation call or by a static call. Any combination of this and the argpos attribute values is possible.

Be careful, for reference purposes only, you can check KiuwanLocalAnalyzer predefined library definitions in [agent_home_dir]/libraries/{tech}