Summary
pac4j is a security framework for Java. pac4j-core prior to version 4.0.0 is affected by a Java deserialization vulnerability. The vulnerability affects systems that store externally controlled values in attributes of the UserProfile class from pac4j-core. It can be exploited by providing an attribute that contains a serialized Java object with a special prefix {#sb64} and Base64 encoding. This issue may lead to Remote Code Execution (RCE) in the worst case. Although a RestrictedObjectInputStream is in place, that puts some restriction on what classes can be deserialized, it still allows a broad range of java packages and potentially exploitable with different gadget chains. pac4j versions 4.0.0 and greater are not affected by this issue. Users are advised to upgrade. There are no known workarounds for this vulnerability.
Impact
Untrusted serialized data is processed by a deserializer that can instantiate arbitrary objects or execute code as a side effect. Typical impact: arbitrary code execution or logic abuse.
CVE-2023-25581 has a CVSS score of 9.8 (Critical). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (4.0.0); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
Remediation advice
Kodem Kai can prioritize this vulnerability in your dependency tree and generate a fix recommendation.
Frequently Asked Questions
- What is CVE-2023-25581? CVE-2023-25581 is a critical-severity insecure deserialization vulnerability in org.pac4j:pac4j-core (maven), affecting versions < 4.0.0. It is fixed in 4.0.0. Untrusted serialized data is processed by a deserializer that can instantiate arbitrary objects or execute code as a side effect.
- How severe is CVE-2023-25581? CVE-2023-25581 has a CVSS score of 9.8 (Critical). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of org.pac4j:pac4j-core are affected by CVE-2023-25581? org.pac4j:pac4j-core (maven) versions < 4.0.0 is affected.
- Is there a fix for CVE-2023-25581? Yes. CVE-2023-25581 is fixed in 4.0.0. Upgrade to this version or later.
- Is CVE-2023-25581 exploitable, and should I be worried? Whether CVE-2023-25581 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2023-25581 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2023-25581? Upgrade
org.pac4j:pac4j-coreto 4.0.0 or later.