CVE-2020-27672
📋 TL;DR
CVE-2020-27672 is a race condition vulnerability in Xen hypervisor that leads to use-after-free with superpages. This allows x86 guest OS users to cause host OS denial of service, data corruption, or potentially gain privileges. Affects Xen hypervisor installations with x86 guest virtual machines.
💻 Affected Systems
- Xen Hypervisor
📦 What is this software?
Fedora by Fedoraproject
Leap by Opensuse
Leap by Opensuse
Xen by Xen
⚠️ Risk & Real-World Impact
Worst Case
Guest OS users could gain elevated privileges on the host system, leading to complete compromise of the hypervisor and all guest VMs.
Likely Case
Host OS denial of service causing hypervisor crashes and VM downtime, potentially with data corruption in affected VMs.
If Mitigated
With proper isolation and monitoring, impact limited to denial of service affecting only the targeted VM and host.
🎯 Exploit Status
Requires guest OS user access and exploitation of race condition timing. No public exploit code available.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Xen 4.14.1 and later
Vendor Advisory: http://xenbits.xen.org/xsa/advisory-345.html
Restart Required: Yes
Instructions:
1. Update Xen to version 4.14.1 or later. 2. Apply vendor patches for Xen 4.13.x and earlier versions. 3. Reboot the hypervisor host to load patched kernel modules.
🔧 Temporary Workarounds
Disable superpages
linuxDisable 2MiB and 1GiB superpages to prevent the race condition
xl set-parameters domain-id superpages=0
🧯 If You Can't Patch
- Implement strict access controls to limit guest OS user privileges
- Isolate critical VMs on separate physical hosts from untrusted VMs
🔍 How to Verify
Check if Vulnerable:
Check Xen version: xl info | grep xen_versionCheck Version:
xl info | grep xen_versionVerify Fix Applied:
Verify Xen version is 4.14.1 or later, or check for XSA-345 patch applied📡 Detection & Monitoring
Log Indicators:
- Hypervisor crashes or panics
- Unexpected VM restarts
- Kernel oops messages in host logs
Network Indicators:
- Sudden loss of connectivity to multiple VMs
- Unusual inter-VM communication patterns
SIEM Query:
source="xen.log" AND ("panic" OR "oops" OR "BUG:")🔗 References
- http://lists.opensuse.org/opensuse-security-announce/2020-10/msg00075.html
- http://lists.opensuse.org/opensuse-security-announce/2020-11/msg00025.html
- http://www.openwall.com/lists/oss-security/2021/01/19/7
- http://xenbits.xen.org/xsa/advisory-345.html
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/XIK57QJOVOPWH6RFRNMGOBCROBCKMDG2/
- https://security.gentoo.org/glsa/202011-06
- https://www.debian.org/security/2020/dsa-4804
- https://xenbits.xen.org/xsa/advisory-345.html
- http://lists.opensuse.org/opensuse-security-announce/2020-10/msg00075.html
- http://lists.opensuse.org/opensuse-security-announce/2020-11/msg00025.html
- http://www.openwall.com/lists/oss-security/2021/01/19/7
- http://xenbits.xen.org/xsa/advisory-345.html
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/XIK57QJOVOPWH6RFRNMGOBCROBCKMDG2/
- https://security.gentoo.org/glsa/202011-06
- https://www.debian.org/security/2020/dsa-4804
- https://xenbits.xen.org/xsa/advisory-345.html
