CRITICAL CVSS 9.3
Published: 2026-02-20

CVE-2026-25896

naturalintelligence fast-xml-parser Security Advisory (CVE-2026-25896)
↗ Official NIST NVD Record
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CyberVault Technical Summary

Analyst Synthesis

Technical analysis, exploit verification, and patch instructions for CVE-2026-25896 impacting naturalintelligence fast-xml-parser. Evaluated with CVSS Base Score of 9.3 (CRITICAL).

Original NVD Description

Source: NIST NVD
fast-xml-parser allows users to validate XML, parse XML to JS object, or build XML from JS object without C/C++ based libraries and no callback. From 4.1.3to before 5.3.5, a dot (.) in a DOCTYPE entity name is treated as a regex wildcard during entity replacement, allowing an attacker to shadow built-in XML entities (<, >, &, ", ') with arbitrary values. This bypasses entity encoding and leads to XSS when parsed output is rendered. This vulnerability is fixed in 5.3.5.

📊 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
Changed (S:C)
Impacts components beyond caller authority
Confidentiality
Low (C:L)
Partial information leakage
Integrity
High (I:H)
Total modification of target system
Availability
None (A:N)
No system availability impact

🎯 Affected Versions Matrix

Affected Product naturalintelligence / fast-xml-parser
Affected Versions *
Weakness Enumeration CWE-185

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-2026-25896 impacting naturalintelligence fast-xml-parser.

⚡ Nuclei Detection Template (YAML) cve-2026-25896.yaml
id: cve-2026-25896

info:
  name: naturalintelligence fast-xml-parser - Security Advisory & Vulnerability Scan
  author: cybervault-security-intel
  severity: critical
  description: |
    Automated signature & scanner for CVE-2026-25896 affecting naturalintelligence fast-xml-parser.
    Evaluation: fast-xml-parser allows users to validate XML, parse XML to JS object, or build XML from JS object without C/C++ based libraries and no callback. From ...
  reference:
    - https://cybervault-cve.pages.dev/cve/CVE-2026-25896
  classification:
    cvss-metrics: CVSS:3.1/CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:H/A:N
    cvss-score: 9.3
    cve-id: CVE-2026-25896
    cwe-id: CWE-185
  tags: cve,cve-2026-25896,naturalintelligence,fast-xml-parser,critical

http:
  - method: GET
    path:
      - "{BaseURL}/"
      - "{BaseURL}/api/"
    matchers-condition: and
    matchers:
      - type: status
        status:
          - 200
      - type: word
        words:
          - "fast-xml-parser"
        part: body
🐍 PoC Exploit & Verification Probe (Python 3) poc_cve-2026-25896.py
# Proof-of-Concept Exploit & Verification Probe for CVE-2026-25896
# Target: naturalintelligence fast-xml-parser | CVSS: 9.3 (CRITICAL)
# Educational & Security Audit Purpose Only

import requests
import sys

def verify_vulnerability(target_url):
    print(f"[*] Auditing {target_url} for CVE-2026-25896 (naturalintelligence fast-xml-parser)...")
    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 naturalintelligence fast-xml-parser 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-2026-25896.sh
# Recommended Remediation & Patching Commands for CVE-2026-25896
# 1. Update package via distribution package manager:
sudo apt-get update && sudo apt-get --only-upgrade install fast-xml-parser 2>/dev/null || \
sudo dnf upgrade fast-xml-parser 2>/dev/null || \
sudo yum update fast-xml-parser

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

# 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-2026-25896 in naturalintelligence fast-xml-parser?

Review vendor-specific security notices and update naturalintelligence fast-xml-parser 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-2026-25896?

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-2026-25896?

CVE-2026-25896 is classified with a CVSS 3.1 Base Score of 9.3 (CRITICAL). Check the metric breakdown above for attack vector requirements.

Risk Snapshot
9.3
CRITICAL SEVERITY
CVE ID CVE-2026-25896
Weakness CWE-185
Vendor naturalintelligence
Product fast-xml-parser
Published 2026-02-20
Vector CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:H/A:N