## Pac4j Java Security Framework Exposed: Critical Deserialization Flaw (CVE-2023-25581) in Core Library
A critical security vulnerability in the widely-used Java authentication and authorization framework, Pac4j, exposes applications to remote code execution. The flaw, tracked as CVE-2023-25581, resides in the `pac4j-core` library versions prior to 4.0.0. It stems from an insecure Java deserialization mechanism within the `UserProfile` class, allowing attackers to potentially execute arbitrary code on affected servers by manipulating stored user attributes.

The vulnerability is triggered when an application stores externally controlled data within a `UserProfile` object's attributes. An attacker can exploit this by injecting a specially crafted attribute value. The exploit uses a specific prefix `{#sb64}` followed by a Base64-encoded serialized Java object. When this malicious data is deserialized by the vulnerable Pac4j version, it can lead to the execution of attacker-controlled code, compromising the entire application server. The issue has been addressed in the newly released major version, `pac4j-core` v4.0.0.

This flaw poses a severe risk to any Java-based web application, API, or service that relies on Pac4j for security, including OAuth, SAML, and CAS implementations. The mandatory upgrade to version 4.0.0 is not merely a feature update but a critical security patch. Development and security teams must immediately audit their dependencies, identify all instances of `org.pac4j:pac4j-core` below version 4.0.0, and apply the update. Failure to patch leaves systems vulnerable to a straightforward attack vector that could result in full server takeover and data breach.
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- **Source**: GitHub Issues
- **Sector**: The Lab
- **Tags**: cybersecurity, vulnerability, java, CVE-2023-25581, deserialization
- **Credibility**: unverified
- **Published**: 2026-04-07 22:27:17
- **ID**: 53863
- **URL**: https://whisperx.ai/en/intel/53863