pac4j Java Framework Vulnerable to RCE Attacks

A critical security vulnerability has been discovered in the popular Java framework pac4j. The vulnerability specifically affects versions before 4.0 of the pac4j-core module.

This vulnerability, identified as CVE-2023-25581, exposes systems to potential remote code execution (RCE) attacks due to a flaw in the deserialization process.

Vulnerability Details – CVE-2023-25581

The issue stems from a Java deserialization vulnerability in the InternalAttributeHandler class of pac4j-core.

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The method restores within this class handles various data types, including strings, booleans, integers, and more.

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However, it also processes serialized Java objects prefixed with {#sb64} and encoded in Base64.

public Object restore(final Object value) {
    if (value != null && value instanceof String) {
        final String sValue = (String) value;
        if (sValue.startsWith(PREFIX)) {
            // Handling different prefixes
            // …
            else if (sValue.startsWith(PREFIX_SB64)) {
                return serializationHelper.unserializeFromBase64(sValue.substring(PREFIX_SB64.length()));
            }
        }
    }
    return value;
}

The vulnerability arises because the restore method does not adequately verify whether a string attribute already contains the {#sb64} prefix.

This oversight allows an attacker to craft a malicious attribute that triggers the deserialization of an arbitrary Java class, potentially leading to RCE.

Coordinated Disclosure Timeline

• 2023-02-02: The vulnerability was reported to the pac4j security team.
• 2023-02-14: The development team acknowledged the report and issued a fix with the release of version 4.0.

Impact and Mitigation

According to a GitHub report, If exploited, this vulnerability could allow attackers to execute arbitrary code on affected systems.

While a RestrictedObjectInputStream is in place to limit deserialization to certain classes, it still permits a wide range of Java packages, making it potentially exploitable with various gadget chains. 

To mitigate this risk, users are strongly advised to upgrade to pac4j-core version 4.0 or later, where this vulnerability has been addressed.

For more information on insecure deserialization and potential exploit techniques, refer to resources like the Ysoserial project.

Users are encouraged to review their systems for potential exposure and promptly apply necessary updates. 

This discovery underscores the importance of secure coding practices and thoroughly validating user-controlled data in software development.

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