---
title: "CVE-2023-25581: pac4j-core affected by a Java deserialization vulnerability"
url: https://erroneo.us/security/cve/CVE-2023-25581/
description: "CVE-2023-25581 (org.pac4j:pac4j-core (Maven)): pac4j is a security framework for Java. pac4j-core prior to version 4.0.0 is affected by a Java…"
type: vulnerability-record
section: "Security Digest"
date_published: 2024-10-10
date_modified: 2024-10-11
publisher: erroneo.us
author: erroneo.us Security Desk
cve: "CVE-2023-25581"
kev: false
cvss: 9.2
epss: 0.01936
license: All rights reserved. Quote with attribution and a link.
---

# CVE-2023-25581: pac4j-core affected by a Java deserialization vulnerability

**Signal:** Critical and remotely reachable. No known exploitation yet, but it is network-reachable without credentials. (Computed from CISA KEV, EPSS and CVSS; not an editorial verdict.)

## Should you act?

- Not in CISA KEV , but CISA’s SSVC assessment records a public proof-of-concept, so attack code exists.
- EPSS 1.9% , percentile 80: FIRST’s model estimates a 1.9% chance of exploitation activity in the next 30 days, higher than 80% of all scored CVEs (moderate). EPSS is a probability, not a verdict.
- Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
- Only applies if your dependency tree includes org.pac4j:pac4j-core (Maven) < 4.0.0, fixed in 4.0.0 . Check your lockfile, including transitive dependencies.

## What it is

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.

## Affected packages

- Maven `org.pac4j:pac4j-core` < 4.0.0 → fixed: 4.0.0

## Affected products (CVE record)

- pac4j pac4j: < 4.0.0

## Severity

- GitHub_M CVSS 4.0: 9.2 `CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N`
- GitHub CVSS 4.0: 9.2 `CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X`

## Exploitation

- CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
- CISA SSVC assessment: exploitation poc , automatable yes , technical impact total .
- FIRST EPSS (model of 2026-10-21): 1.94% probability of exploitation activity in the next 30 days; percentile 80.

## Sources

- [GitHub Advisory GHSA-76mw-6p95-x9x5](https://github.com/advisories/GHSA-76mw-6p95-x9x5)
- [CVE.org record CVE-2023-25581](https://www.cve.org/CVERecord?id=CVE-2023-25581)
- [NVD entry CVE-2023-25581](https://nvd.nist.gov/vuln/detail/CVE-2023-25581)
- [securitylab.github.com](https://securitylab.github.com/advisories/GHSL-2022-085_pac4j/)
- [github.com](https://github.com/frohoff/ysoserial)
- [github.com](https://github.com/pac4j/pac4j/blob/5834aeb22ad3a4369dfa572be60d7b20f5784a8f/pac4j-core/src/main/java/org/pac4j/core/profile/InternalAttributeHandler.java#L95)
- [portswigger.net](https://portswigger.net/web-security/deserialization)
- [securitylab.github.com](https://securitylab.github.com/advisories)

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Source page: https://erroneo.us/security/cve/CVE-2023-25581/ · Security Digest: https://erroneo.us/security/ · More: https://erroneo.us/llms.txt