MEDIUM CVSS 5.5
Published: 2020-12-15

CVE-2020-29566

xen xen Security Advisory (CVE-2020-29566)
↗ Official NIST NVD Record
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CyberVault Technical Summary

Analyst Synthesis

Technical analysis, exploit verification, and patch instructions for CVE-2020-29566 impacting xen xen. Evaluated with CVSS Base Score of 5.5 (MEDIUM).

Original NVD Description

Source: NIST NVD
An issue was discovered in Xen through 4.14.x. When they require assistance from the device model, x86 HVM guests must be temporarily de-scheduled. The device model will signal Xen when it has completed its operation, via an event channel, so that the relevant vCPU is rescheduled. If the device model were to signal Xen without having actually completed the operation, the de-schedule / re-schedule cycle would repeat. If, in addition, Xen is resignalled very quickly, the re-schedule may occur before the de-schedule was fully complete, triggering a shortcut. This potentially repeating process uses ordinary recursive function calls, and thus could result in a stack overflow. A malicious or buggy stubdomain serving a HVM guest can cause Xen to crash, resulting in a Denial of Service (DoS) to the entire host. Only x86 systems are affected. Arm systems are not affected. Only x86 stubdomains serving HVM guests can exploit the vulnerability.

📊 CVSS v3.1 Metric Breakdown

Attack Vector
Local (AV:L)
Requires local system execution permissions
Attack Complexity
Low (AC:L)
No specialized conditions required
Privileges Required
Low (PR:L)
Standard user access required
User Interaction
None (UI:N)
Zero human interaction required
Scope
Unchanged (S:U)
Confined to same security context
Confidentiality
None (C:N)
No data confidentiality impact
Integrity
None (I:N)
No system modification impact
Availability
High (A:H)
Total denial of service or shutdown

🎯 Affected Versions Matrix

Affected Product xen / xen
Affected Versions *
Weakness Enumeration CWE-674

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-2020-29566 impacting xen xen.

⚡ Nuclei Detection Template (YAML) cve-2020-29566.yaml
id: cve-2020-29566

info:
  name: xen xen - Security Advisory & Vulnerability Scan
  author: cybervault-security-intel
  severity: medium
  description: |
    Automated signature & scanner for CVE-2020-29566 affecting xen xen.
    Evaluation: An issue was discovered in Xen through 4.14.x. When they require assistance from the device model, x86 HVM guests must be temporarily de-scheduled. Th...
  reference:
    - https://cybervault-cve.pages.dev/cve/CVE-2020-29566
  classification:
    cvss-metrics: CVSS:3.1/CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
    cvss-score: 5.5
    cve-id: CVE-2020-29566
    cwe-id: CWE-674
  tags: cve,cve-2020-29566,xen,xen,medium

http:
  - method: GET
    path:
      - "{BaseURL}/"
      - "{BaseURL}/api/"
    matchers-condition: and
    matchers:
      - type: status
        status:
          - 200
      - type: word
        words:
          - "xen"
        part: body
🐍 PoC Exploit & Verification Probe (Python 3) poc_cve-2020-29566.py
# Proof-of-Concept Exploit & Verification Probe for CVE-2020-29566
# Target: xen xen | CVSS: 5.5 (MEDIUM)
# Educational & Security Audit Purpose Only

import requests
import sys

def verify_vulnerability(target_url):
    print(f"[*] Auditing {target_url} for CVE-2020-29566 (xen xen)...")
    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 xen xen 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-2020-29566.sh
# Recommended Remediation & Patching Commands for CVE-2020-29566
# 1. Update package via distribution package manager:
sudo apt-get update && sudo apt-get --only-upgrade install xen 2>/dev/null || \
sudo dnf upgrade xen 2>/dev/null || \
sudo yum update xen

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

# 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-2020-29566 in xen xen?

Review vendor-specific security notices and update xen xen 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-2020-29566?

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-2020-29566?

CVE-2020-29566 is classified with a CVSS 3.1 Base Score of 5.5 (MEDIUM). Check the metric breakdown above for attack vector requirements.

Risk Snapshot
5.5
MEDIUM SEVERITY
CVE ID CVE-2020-29566
Weakness CWE-674
Vendor xen
Product xen
Published 2020-12-15
Vector CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H