The OWASP Enterprise Security API (ESAPI) is a powerful open-source tool designed to help Java web application developers protect their applications from common vulnerabilities. In late 2022, a subtle but significant security issue was discovered in ESAPI’s directory path validation logic, tracked as CVE-2022-23457.

Let’s break down what happened, why it matters, and how you can protect your applications.

What Is CVE-2022-23457?

CVE-2022-23457 affects ESAPI versions prior to 2.3... Specifically, it concerns the default implementation of the method:

Validator.getValidDirectoryPath(String context, String input, File parent, boolean allowNull)

This method is supposed to confirm that a given file path is actually a child of a specified parent directory — a crucial check to defend against path traversal attacks.

The flaw: The method doesn’t always properly verify if the input string (the path you want to use) is really "under" the specified parent directory. It could be tricked, especially if attackers control the path input, to allow access to files outside the intended directory tree.

Understanding the Risk – Why Is This Bad?

Suppose you have a web application that lets users download files, and you want them restricted to only fetching files from /var/www/files. Here’s how a developer might use ESAPI:

File parent = new File("/var/www/files");
String userInput = request.getParameter("file");

String safePath = ESAPI.validator().getValidDirectoryPath("fileDownload", userInput, parent, false);

If the flaw is present, a user could provide input like

../../../../etc/passwd

or even sneakier strings, making the method believe the path is still inside /var/www/files, allowing downloads of sensitive files elsewhere on the system.

Vulnerable Version (Before 2.3..):

// Vulnerable: Attacker controls 'input'
String result = ESAPI.validator().getValidDirectoryPath(
    "context",             // Context for logging
    "../../etc/passwd",    // Attacker-controlled input
    new File("/var/www/files"),
    false                  // Do not allow nulls
);
// Might return path outside /var/www/files!

Fixed Version (2.3.. and Later):

The internal logic now strictly ensures the resolved path is a real descendant of the parent directory.

// Secure: Returns null or errors out if 'input' escapes parent
String result = ESAPI.validator().getValidDirectoryPath(
    "context",
    "../../etc/passwd",
    new File("/var/www/files"),
    false
);
// Will correctly block traversal attempts

Patch:
You can see the mitigation in the ESAPI codebase.

Exploiting the Vulnerability

An attacker who can submit file or directory paths (say, through file upload, download, or logs) could use classic directory traversal tricks:

- "../../../etc/passwd"

"..%2F..%2F..%2Fetc%2Fpasswd" (using URL encoding)

- "subdir/../../../../etc/shadow"

If ESAPI’s getValidDirectoryPath is not patched, these might slip past. The method would wrongly treat such input as a valid child, giving access to sensitive files.

Suppose you let users view images from /var/www/files/avatars. An attacker tries

/../../../etc/passwd

If unchecked, your download servlet might expose system files.

*Immediately upgrade to ESAPI v2.3.. or later*.

Find the latest release here: ESAPI Releases on GitHub

Avoid Custom Implementations

While you *can* write your own Validator, the maintainers do not recommend this unless you are confident you know all the pitfalls.

Canonicalize paths

- Forbid dangerous characters/sequences (like .., /, \)

References and Further Reading

- CVE-2022-23457 at NVD
- ESAPI GitHub Issue and Fix
- Official ESAPI Documentation
- OWASP File Path Traversal Cheat Sheet

Takeaway

CVE-2022-23457 is a stark reminder: even trusted security libraries may contain subtle bugs. Directory traversal remains a favorite attack vector, so when using ESAPI or similar tools, always stay up to date, review your validation logic, and keep an eye out for security advisories.

If you’re still on an older ESAPI:  
Upgrade NOW to 2.3..+ – don’t DIY your validator logic unless you really need to!

Stay safe, code securely, and always validate those file paths.


*This post was crafted exclusively for developers seeking clarity on emerging security flaws. Have questions about implementation specifics? Let us know!*

Timeline

Published on: 04/25/2022 20:15:00 UTC
Last modified on: 07/25/2022 18:21:00 UTC