Understanding the Dangers of XML Injection and How to Protect Against Them

Quick Summary: The risk of XML injection can be avoided by only understanding it to the core. Our article will give you a deeper understanding of this threat vector. Plus, we will discuss some effective ways to prevent this threat. Keep reading to get more insights for enhanced security.

Cybersecurity incidents and data breaches are not new. They are widespread and increasing every year. As per data, the cost of cybercrimes to the world will be around $10 trillion annually by 2025. It’s an alarming situation for organizations.

Attackers use a myriad of different attack tactics to cause cybersecurity incidents. Knowing and finding ways to prevent such attacks can help you protect your digital assets. One such attack tactic is XML injection.

XML injection occurs when an attacker includes a malicious external entity into a web app’s XML document. It could lead to sensitive data exposure, remote code execution, and other types of security issues.

Stay tuned to this article for detailed information on XML injection. It will provide the necessary information to help you secure your digital assets. Let’s keep going with the rhythm.

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What is XML Injection?

XML Injection is a cyberattack technique in which a web application processes XML insecurely. This means that the web app parses user-supplied XML data without proper input validation and sanitization. This type of data, when added to the web app’s XML document, can cause various security problems.

Attackers can take advantage of XML metacharacters such as “<”, “>”, “&”, “,”, and more to manipulate XML documents. It is possible to interrupt application logic that will enable an attacker to access sensitive data or perform unauthorized actions.

How Does an XML Injection Attack Work?

Let’s understand this with an example. Suppose a web app uses XML, as given below. It also uses DTDs (Document Type Definitions) for defining entities. It uses URI to fetch external DTDs.

<?xml version="1.0" encoding="UTF-8"?>  <!DOCTYPE user [ <!ENTITY example SYSTEM “<https://example.com/test.dtd>”>]  <users>  <user>  <username>abcd</username>  <password>pa55w0rd</password>  <userid>000</userid>  </user>  <user>  <username>xyz</username>  <password>pssw0rd</password>  <userid>001/userid>  </user>  </users>

If external entities are allowed by your web application, the above XML will be parsed and processed. After the contents of the external URI will be added to the existing XML file. An attacker can exploit it by modifying it and could include a malicious external entity, as given below.

<?xml version="1.0" encoding="UTF-8"?>  <!DOCTYPE user [ <!ENTITY example SYSTEM "file:///etc/passwd"> ] >  <users>  <user>  <username>abcd</username>  <password>pa55w0rd</password>  <userid>000</userid>  </user>  <user>  <username>xyz</username>  <password>pssw0rd</password>  <userid>001/userid>  </user>  </users>

In the above XML, the URI points to a sensitive server file. When the processing of external entities is allowed, they will be processed, and the contents of the file will be returned. Even if there is a parsing error, the contents will be returned in the error. As a result, an attacker can obtain crucial server information that can help gain unauthorized access.

XML Injection Attack: The Impact

An XML injection attack occurs when an attacker manipulates an XML input to alter the behavior of an application that processes XML data. Check out the key points.

Malicious Input

The attacker creates malicious XML content and submits it via user inputs or other data mediums that are usually processed by the application.

Injection into XML Data

The malicious XML is injected into the application’s XML processing logic. This can be performed via parameters, form fields, or other entry points where XML data is often acknowledged.

Altered XML Parsing

When the application parses the XML data, the injected content can modify the studied structure or behavior. For example, it might change XML tags, release unexpected data, or misuse attributes.

Execution of Malicious Actions

Depending on the application's handling of the injected XML, it often lead to varied harmful outcomes like unauthorized access to data and execution of unnecessary commands.

Manipulation of Vulnerabilities

If the system does not properly authenticate or sanitize the XML input, the attacker can get a chance to execute nasty actions like data leakage, denial of service, or even remote code execution.

What are the Types of XML Injection?

XML injection attacks differ based on the type of payload used. Preventing this type of attack requires an understanding of these types. Let’s check the different XML injection attack types.

XPath Injection

In this type of XML injection attack, an attacker uses XPath expression to send malicious commands or data to an XML database or document. XPath is a syntax that uses path expressions like “/folder/data” to select nodes in an XML document. After this, the path is followed to choose the node.

Using the XPath tactic, an attacker can add new elements or modify existing ones in an XML-based database. This could result in compromised web application security. The developers can also attack SOAP APIs as they also work on XML for data exchange.

XML Entity Expansion

XEE or XML Entity Expansion is another attack tactic in which an attacker takes advantage of a vulnerability in XML specification. By exploiting this vulnerability, the attacker can define XML entities that reference other entities in an XML document.

Since the defined XML entity can affect other entities in the document, an attacker can modify or remove entities. Consequently, it could open a door for more vulnerabilities that may allow the attacker to gain access to crucial data.

XQuery Injection

XQuery is a query language just like SQL. It is used to query XML data. An attacker can inject a malicious XQuery input to push unauthorized information to your XML database. It will enable the attacker to execute a malicious command. The attacker can leverage XQuery characters to carry out the injection attack and manipulate sensitive data in your XML database.

XML External Entity

By default, external references are permitted by an XML parser. If you have not disabled it for your application and it processes XML documents or data provided by users with this setting, it could result in an XML External Entity or XXE injection attack.

Blind XPath Injection

It is a type of XML injection attack in which the attacker doesn’t know the structure of an XML document. In this case, the attacker attempts to gather information one by one using true/false or Boolean queries. The attackers can cause parsing errors or leverage methods such as out-of-band data exfiltration to get sensitive information.

Attackers can leverage vulnerability in applications that generate error messages in response. In this case, an attacker can trigger parsing errors. The attacker can use bad external DTDs to cause parsing errors.

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What are the Risks of XML Injection Attack?

There are many dangerous consequences when an attacker injects malicious entities into XML. For example, your data could get leaked, or an attacker can take control of the server after a successful attack. The following are the potential risks of XML injection.

Denial of Service (DoS)

An attacker can use a malicious XML injection payload to overburden a server with excessive resource consumption. It results in a Denial of Service or DoS attack. It will cause disruptions in your services owing to downtime and affect user experience. It will impact brand reputation, user trust, and business operations.

Sensitive Data Exposure

The potential of sensitive data exposure is a critical risk associated with XML injection threat. Attackers can manipulate XML input to extract sensitive data from a vulnerable web application. Your confidential data could go into the hands of malicious actors. It will affect your business reputation and attract legal action.

Server-side Request Forgery

An attacker can perform an SSRF or Server-side Request Forgery attack by exploiting XXE injection vulnerability. In an SSRF attack, a web application is forced to make requests to an external malicious URL. The attacker could load bad scripts from the external server. The attacker will define an external entity and add the targeted URL. The entity is used in the response data.

Remote Code Execution

A successful XML injection attack can also allow an attacker to execute arbitrary code on the server. It could be system-level commands that could enable an attacker to gain complete access to a web application. The attacker can leverage RCE or Remote Code Execution to install malware on the server, manipulate data, or damage server functionality.

What are the Best Ways to Prevent XML Injection?

You can avoid a costly data breach, disruption in business operations, compromised servers, and other risks by preventing XML injection threats. So, how can you do it? The following XML injection prevention tips can help you avoid such cyber threats.

Sanitize and Validate Input

Processing inputs without proper sanitization and validation is a serious security flaw. It could allow an attacker to insert malicious code in the input that will be processed by a vulnerable web app. However, input validation and sanitization help to prevent many types of web app security risks.

Input validation is a technique in which data provided by users through forms or other means is checked on various conditions. The data is checked to ensure it meets the required constraints. On the other hand, sanitization removes unwanted characters from the data that could be malicious.

When proper input validation and sanitization are applied, the web application will process only valid data. It will reduce the chances of potential cyberattacks.

Use an Allowlist

One proactive method to prevent XXE attacks is by using a whitelist or allowlist of XML entities, attributes, and elements. The list can define all the elements, entities, and attributes that are valid for your web application and prevent processing unwanted data.

There can be a logic in your web application that checks the user-supplied data against the contents of the allowlist to ensure it is valid.

Regular Security Checks

Apart from coding-level adjustments, you must also perform regular security testing with an efficient web application vulnerability scanner. By performing security testing on your web app when it is built and running in production, you can discover potential vulnerabilities. You can remediate them and protect your web app from XML injection attacks and other threats.

With proactive vulnerability assessment, you can rapidly find and patch vulnerabilities to keep your systems secure. Regular vulnerability scanning and remediation will help you keep your web apps secure from emerging threats.

Remove DTD Support

Attackers can exploit legacy external DTD features if your web application supports it. By exploiting this feature, attackers can include malicious code in your XML document. You can avoid the risk of XML entity injection by disabling this feature for your web app.

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To Sum Up

XML injection is a serious security challenge for web apps that process XML data. It can result in compromised security and sensitive data exposure. Organizations must remain vigilant and follow the best practices to avoid such risks.

Conducting thorough vulnerability scanning and staying informed of emerging security threats will help organizations eliminate risks. You need a powerful DAST tool like ZeroThreat to conduct thorough scanning and discover vulnerabilities.

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