CVE-2020-29481 – This Xen vulnerability allows a newly created g... (How to Fix)

Q: What is the severity of CVE-2020-29481?

CVE-2020-29481 has a CVSS score of 8.8 (HIGH). This Xen vulnerability allows a newly created guest domain to inherit access rights to Xenstore nodes from previously destroyed domains with the same domain ID (domid). This can lead to unauthorized reading of sensitive information from other running guest domains. All Xen installations through version 4.14.x are affected.

📋 TL;DR

This Xen vulnerability allows a newly created guest domain to inherit access rights to Xenstore nodes from previously destroyed domains with the same domain ID (domid). This can lead to unauthorized reading of sensitive information from other running guest domains. All Xen installations through version 4.14.x are affected.

💻 Affected Systems

Products:

Xen Hypervisor

Versions: All versions through 4.14.x

Operating Systems: Linux distributions running Xen (Fedora, Debian, etc.)

Default Config Vulnerable: ⚠️ Yes

Notes: Both Xenstore implementations (C and Ocaml) are vulnerable. Only affects Xenstore entries of other guests still running, as /local/domain/<domid> entries are deleted when a guest is destroyed.

📦 What is this software?

⚠️ Risk & Real-World Impact

🔴

Worst Case

A malicious guest domain could read sensitive configuration data, credentials, or secrets from other guest domains, potentially leading to privilege escalation or data breach across the virtualization environment.

🟠

Likely Case

Information disclosure where new guests can access Xenstore entries of other running guests, potentially exposing configuration details or operational data.

🟢

If Mitigated

Limited impact if proper domain isolation and monitoring are in place, with no direct code execution or denial of service.

🌐 Internet-Facing: LOW - This vulnerability requires access to the Xen hypervisor management layer and is not directly exploitable from the internet.

🏢 Internal Only: HIGH - This affects the core virtualization infrastructure and can be exploited by any guest domain with malicious intent within the environment.

🎯 Exploit Status

Public PoC: ✅ No

Weaponized: UNKNOWN

Unauthenticated Exploit: ✅ No

Complexity: MEDIUM

Exploitation requires creating a new domain with the same domid as a previously destroyed domain and understanding Xenstore access patterns.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: Xen 4.14.1 and later

Vendor Advisory: https://xenbits.xenproject.org/xsa/advisory-322.html

Restart Required: Yes

Instructions:

1. Update Xen to version 4.14.1 or later. 2. Apply vendor-specific patches for your distribution. 3. Reboot the hypervisor host to load the updated Xen components.

🔧 Temporary Workarounds

Avoid domain ID reuse

linux

Prevent new domains from reusing the same domid as previously destroyed domains

Configure Xen to use unique domain IDs and avoid recycling IDs

🧯 If You Can't Patch

Implement strict monitoring of Xenstore access patterns and domain creation events
Isolate sensitive guest domains from potentially malicious guests using separate virtualization clusters

🔍 How to Verify

Check if Vulnerable:

Check Xen version with 'xl info' or 'xm info' and verify if it's 4.14.x or earlier

Check Version:

xl info | grep xen_version || xm info | grep xen_version

Verify Fix Applied:

Verify Xen version is 4.14.1 or later using 'xl info' or 'xm info'

📡 Detection & Monitoring

Log Indicators:

Unusual Xenstore access patterns
Domain creation events with reused domain IDs
Access violations in Xenstore logs

Network Indicators:

None - this is a hypervisor-level vulnerability

SIEM Query:

Search for Xen hypervisor logs showing domain creation with previously used domain IDs or unauthorized Xenstore access attempts

📊 Metadata

CVE ID: CVE-2020-29481

CVSS v3 Score: 8.8 (HIGH)

CVSS Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H

CWE: CWE-269

Published: December 15, 2020

Last Updated: November 21, 2024

🔗 References

http://www.openwall.com/lists/oss-security/2020/12/16/3 Mailing List,Third Party Advisory
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/2C6M6S3CIMEBACH6O7V4H2VDANMO6TVA/
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/OBLV6L6Q24PPQ2CRFXDX4Q76KU776GKI/
https://www.debian.org/security/2020/dsa-4812 Third Party Advisory
https://xenbits.xenproject.org/xsa/advisory-322.html Patch,Vendor Advisory
http://www.openwall.com/lists/oss-security/2020/12/16/3 Mailing List,Third Party Advisory
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/2C6M6S3CIMEBACH6O7V4H2VDANMO6TVA/
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/OBLV6L6Q24PPQ2CRFXDX4Q76KU776GKI/
https://www.debian.org/security/2020/dsa-4812 Third Party Advisory
https://xenbits.xenproject.org/xsa/advisory-322.html Patch,Vendor Advisory

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