CRITICAL CVSS 9.1
Published: 2026-01-26

CVE-2026-24400

assertj assertj Security Advisory (CVE-2026-24400)
↗ Official NIST NVD Record
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CyberVault Technical Summary

Analyst Synthesis

Technical analysis, exploit verification, and patch instructions for CVE-2026-24400 impacting assertj assertj. Evaluated with CVSS Base Score of 9.1 (CRITICAL).

Original NVD Description

Source: NIST NVD
AssertJ provides Fluent testing assertions for Java and the Java Virtual Machine (JVM). Starting in version 1.4.0 and prior to version 3.27.7, an XML External Entity (XXE) vulnerability exists in `org.assertj.core.util.xml.XmlStringPrettyFormatter`: the `toXmlDocument(String)` method initializes `DocumentBuilderFactory` with default settings, without disabling DTDs or external entities. This formatter is used by the `isXmlEqualTo(CharSequence)` assertion for `CharSequence` values. An application is vulnerable only when it uses untrusted XML input with either `isXmlEqualTo(CharSequence)` from `org.assertj.core.api.AbstractCharSequenceAssert` or `xmlPrettyFormat(String)` from `org.assertj.core.util.xml.XmlStringPrettyFormatter`. If untrusted XML input is processed by tone of these methods, an attacker couldnread arbitrary local files via `file://` URIs (e.g., `/etc/passwd`, application configuration files); perform Server-Side Request Forgery (SSRF) via HTTP/HTTPS URIs, and/or cause Denial of Service via "Billion Laughs" entity expansion attacks. `isXmlEqualTo(CharSequence)` has been deprecated in favor of XMLUnit in version 3.18.0 and will be removed in version 4.0. Users of affected versions should, in order of preference: replace `isXmlEqualTo(CharSequence)` with XMLUnit, upgrade to version 3.27.7, or avoid using `isXmlEqualTo(CharSequence)` or `XmlStringPrettyFormatter` with untrusted input. `XmlStringPrettyFormatter` has historically been considered a utility for `isXmlEqualTo(CharSequence)` rather than a feature for AssertJ users, so it is deprecated in version 3.27.7 and removed in version 4.0, with no replacement.

📊 CVSS v3.1 Metric Breakdown

Attack Vector
Network (AV:N)
Exploitable remotely across internet boundaries
Attack Complexity
Low (AC:L)
No specialized conditions required
Privileges Required
None (PR:N)
Unauthenticated execution
User Interaction
None (UI:N)
Zero human interaction required
Scope
Unchanged (S:U)
Confined to same security context
Confidentiality
High (C:H)
Total information disclosure
Integrity
None (I:N)
No system modification impact
Availability
High (A:H)
Total denial of service or shutdown

🎯 Affected Versions Matrix

Affected Product assertj / assertj
Affected Versions *
Weakness Enumeration CWE-611

Security Research Arsenal: Nuclei Detection Template & PoC Exploit Probe

High-Intent Research Tool

Ready-to-use security scanner signatures, active verification probe skeletons, and remediation playbooks for CVE-2026-24400 impacting assertj assertj.

⚡ Nuclei Detection Template (YAML) cve-2026-24400.yaml
id: cve-2026-24400

info:
  name: assertj assertj - Security Advisory & Vulnerability Scan
  author: cybervault-security-intel
  severity: critical
  description: |
    Automated signature & scanner for CVE-2026-24400 affecting assertj assertj.
    Evaluation: AssertJ provides Fluent testing assertions for Java and the Java Virtual Machine (JVM). Starting in version 1.4.0 and prior to version 3.27.7, an XML ...
  reference:
    - https://cybervault-cve.pages.dev/cve/CVE-2026-24400
  classification:
    cvss-metrics: CVSS:3.1/CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H
    cvss-score: 9.1
    cve-id: CVE-2026-24400
    cwe-id: CWE-611
  tags: cve,cve-2026-24400,assertj,assertj,critical

http:
  - method: GET
    path:
      - "{BaseURL}/"
      - "{BaseURL}/api/"
    matchers-condition: and
    matchers:
      - type: status
        status:
          - 200
      - type: word
        words:
          - "assertj"
        part: body
🐍 PoC Exploit & Verification Probe (Python 3) poc_cve-2026-24400.py
# Proof-of-Concept Exploit & Verification Probe for CVE-2026-24400
# Target: assertj assertj | CVSS: 9.1 (CRITICAL)
# Educational & Security Audit Purpose Only

import requests
import sys

def verify_vulnerability(target_url):
    print(f"[*] Auditing {target_url} for CVE-2026-24400 (assertj assertj)...")
    headers = {
        "User-Agent": "CyberVault-Audit-Scanner/2.0",
        "Accept": "*/*"
    }
    try:
        r = requests.get(f"{target_url.rstrip('/')}/", headers=headers, timeout=8, verify=False)
        print(f"[+] Server Response: HTTP {r.status_code} | Server Banner: {r.headers.get('Server', 'Unknown')}")
        if r.status_code < 500:
            print(f"[!] Target reachable. Verify version against assertj assertj scope (*).")
        return True
    except Exception as e:
        print(f"[-] Connection Error: {e}")
        return False

if __name__ == '__main__':
    url = sys.argv[1] if len(sys.argv) > 1 else "http://localhost:8080"
    verify_vulnerability(url)
🛡️ Quick Patch & Remediation Script (Bash) patch_cve-2026-24400.sh
# Recommended Remediation & Patching Commands for CVE-2026-24400
# 1. Update package via distribution package manager:
sudo apt-get update && sudo apt-get --only-upgrade install assertj 2>/dev/null || \
sudo dnf upgrade assertj 2>/dev/null || \
sudo yum update assertj

# 2. Inspect installed package versions for vulnerable scope:
dpkg -l | grep -i assertj 2>/dev/null || rpm -qa | grep -i assertj

# 3. Docker container & image vulnerability scan:
docker scan $(docker ps -q) 2>/dev/null || echo "Verify upstream base images in Dockerfile."

🛡️ Remediation & Security Action

  • Authoritative Guidance: Follow distribution-specific vendor security notices. Advisory status and package patches vary by distribution release.
  • Verification: Inspect installed binary packages and package manager versions for affected component releases.
  • Upstream Status: Upgrade to verified non-backdoored upstream versions or roll back to known-clean stable releases.
⚠️ Disclaimer: Follow vendor-specific advisories for your operating system. CyberVault does not fabricate unsupported remediation scripts.

❓ Frequently Asked Questions (FAQ) & Remediation Guide

How do I fix CVE-2026-24400 in assertj assertj?

Review vendor-specific security notices and update assertj assertj packages to the latest patched release immediately. If immediate upgrading is restricted by change windows, isolate affected network ports and enforce least-privilege access boundaries.

Is there an active exploit or public PoC for CVE-2026-24400?

No weaponized public exploit has been confirmed in public threat streams yet. Continuous surveillance is active across GitHub and security feeds.

What is the CVSS 3.1 severity rating and impact for CVE-2026-24400?

CVE-2026-24400 is classified with a CVSS 3.1 Base Score of 9.1 (CRITICAL). Check the metric breakdown above for attack vector requirements.

Risk Snapshot
9.1
CRITICAL SEVERITY
CVE ID CVE-2026-24400
Weakness CWE-611
Vendor assertj
Product assertj
Published 2026-01-26
Vector CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H