Understanding XPath Injection: Risks And Mitigation

Many web applications and APIs run on XML and XPath, which is advantageous for effective communication and data transmission. However, it runs the risk of an XPath injection attack, which can create major problems for your organization if left unchecked. The good news is that by implementing best practices and using effective protection solutions, you can reduce your risk of compromise.

What is XPath Injection?

Although XML is perhaps not as widely used as it once was, many complex applications still use it for data storage and execution instructions. XML Path Language, also known as XPath, is used to search XML documents for specific data of interest. XML and XPath are used in many APIs, which act as middlemen between web applications and websites, mobile apps, and other web applications.

Naturally, this means there is quite a bit of data behind XPath, and attackers attempt to access that data through an attack called XPath injection. This attack exploits user inputs, such as login information, to XPath by making a query using malformed inputs. XML documents are supposed to only parse queries if they are well-formed, but this can be circumvented if proper security controls are not in place.

Without adequate protection around your XML document or API, these inputs can provide the attacker with unauthorized access to your network, data, and other assets. Because XML documents contain both data and instructions to devices and applications regarding how they should use that data, XPath injection attacks can be very damaging to your organization, especially if you don’t catch them right away.

Potential Impacts of XPath Injection

XML documents are something of a repository for information behind your API or app. They are also somewhat simple to modify due to the way they are structured (conversely, they are particular about structure and can be broken with the right inputs). If an attacker gains access, there are several potential consequences, none of them positive:

1. Data theft:

Especially when XML documents are not encrypted, accessing the information in the file is not difficult. As a result, it’s relatively simple for an attacker who performs an XPath injection to access, copy, and steal your data. Alternatively, an attacker might delete your data as part of a ransom attempt.

2. Privilege Escalation:

Cyberattacks tend to be more manageable when attackers have basic privileges and begin making changes right away. Those attackers are usually caught quickly and expelled, and most of the damage is fixable without significant downtime. However, in an XPath injection attack, attackers are often able to fly under the radar and give themselves additional privileges, which means the attacks last longer, are harder to pin down, and are more severe due to increased data and infrastructure access.

3. Compromised credentials:

Usernames and passwords in the XML document can be stolen and tested on other websites. This puts your customers at risk of identity theft and will likely damage your reputation. You may also face litigation from your customers and could be fined for mishandling data, depending on where you operate.

4. Modified App Behavior:

By changing XPath, attackers can change the behavior of your application. This can cause it to bypass further authentication or expose even protected information.

5. DDoS Attacks:

By changing XPath inputs, attackers can force the application to use high amounts of system resources. This causes the app to be unresponsive to other (legitimate) queries, which is a problem for your customers trying to interact with your app or access their own information.

XPath injection is not a very sophisticated attack, but it’s very effective if your XML documents are not properly secured.

Best Practices for Mitigating XPath Injection

To prevent XPath attacks, it’s important to use a variety of safeguards in both your XML documents and your application or API.

To secure XML documents, consider implementing:

1. Input validation. Essentially quality testing, input validation checks for malformations and ensures substandard inputs are not accepted.

2. Parameterized queries. By differentiating between user inputs and the query itself, this prevents attackers from altering the query (and thus the XML code).

3. Input sanitization. Depending on your approach, input sanitization will either block known malicious inputs or only accept known benign inputs, which prevents malicious code from being packaged with an input.

As for your application or API, use a WAF or WAAP solution to block attempted exploits. WAFs act as a first line of defense against attacks for your applications, and WAAPs do the same for APIs. Both can help keep attackers away from your XML documents. While you should still implement the requisite security measures for the documents themselves, WAF and WAAP will reduce the number of threats that come through by selectively blocking activity.

WAF and WAAP operate based on rules that you create based on the needs of your environment. Using these rules, and machine learning if you find a sophisticated solution, they block activity that does not match typical use patterns while allowing your legitimate traffic to continue accessing the app. They also monitor traffic and will alert you to atypical activity, which can help you pinpoint a potential attack early.

If your app or API runs on XML, XPath injection attacks are a significant risk to your organization. However, using best practices and protecting your assets with WAF and WAAP solutions can help prevent and mitigate these attacks, keeping your sensitive information and your customers’ data safe.