CVE-2020-11739
📋 TL;DR
A memory barrier vulnerability in Xen's read-write unlock paths allows guest OS users to exploit race conditions, potentially causing denial of service, memory leaks, or privilege escalation. This affects Xen hypervisor versions through 4.13.x, impacting virtualized environments using Xen for virtualization.
💻 Affected Systems
- Xen Hypervisor
📦 What is this software?
Fedora by Fedoraproject
Fedora by Fedoraproject
Fedora by Fedoraproject
Leap by Opensuse
Xen by Xen
Xen by Xen
Xen by Xen
⚠️ Risk & Real-World Impact
Worst Case
Privilege escalation allowing guest to gain hypervisor-level control, memory corruption leading to hypervisor crash, or sensitive information leakage from hypervisor memory.
Likely Case
Denial of service through hypervisor crash or memory exhaustion from memory leaks, disrupting all virtual machines on the host.
If Mitigated
Limited impact if proper isolation and monitoring are in place, though race condition exploitation remains possible.
🎯 Exploit Status
Exploitation requires guest VM access and precise timing to trigger race conditions. No public exploit code available at disclosure.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Xen 4.14 and later, or security patches for affected versions
Vendor Advisory: http://xenbits.xen.org/xsa/advisory-314.html
Restart Required: Yes
Instructions:
1. Update Xen to version 4.14 or later. 2. Apply security patches from your distribution if available. 3. Reboot hypervisor host after patching. 4. Verify patch application with version check.
🔧 Temporary Workarounds
Restrict Grant Table Hypercalls
linuxLimit guest access to grant-table hypercalls that could trigger the vulnerability
# Configure Xen to restrict XENMAPSPACE_grant_table usage
# Review and limit hypercall permissions in Xen configuration
🧯 If You Can't Patch
- Isolate vulnerable Xen hosts from critical networks
- Implement strict monitoring for hypervisor crashes or abnormal memory usage
🔍 How to Verify
Check if Vulnerable:
Check Xen version with 'xl info' or 'xm info' and compare against affected versions (≤4.13.x)Check Version:
xl info | grep xen_version || xm info | grep xen_versionVerify Fix Applied:
Verify Xen version is 4.14 or later, or check for applied security patches from distribution📡 Detection & Monitoring
Log Indicators:
- Hypervisor crash logs
- Abnormal memory allocation patterns in Xen logs
- Repeated grant-table hypercall failures
Network Indicators:
- Sudden loss of connectivity to all VMs on a host
- Unusual hypervisor management traffic patterns
SIEM Query:
source="xen.log" AND ("crash" OR "panic" OR "memory leak" OR "grant-table")🔗 References
- http://lists.opensuse.org/opensuse-security-announce/2020-05/msg00006.html
- http://www.openwall.com/lists/oss-security/2020/04/14/2
- http://xenbits.xen.org/xsa/advisory-314.html
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/5M2XRNCHOGGTJQBZQJ7DCV6ZNAKN3LE2/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/NVTP4OYHCTRU3ONFJOFJQVNDFB25KLLG/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/YMAW7D2MP6RE4BFI5BZWOBBWGY3VSOFN/
- https://security.gentoo.org/glsa/202005-08
- https://www.debian.org/security/2020/dsa-4723
- https://xenbits.xen.org/xsa/advisory-314.html
- http://lists.opensuse.org/opensuse-security-announce/2020-05/msg00006.html
- http://www.openwall.com/lists/oss-security/2020/04/14/2
- http://xenbits.xen.org/xsa/advisory-314.html
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/5M2XRNCHOGGTJQBZQJ7DCV6ZNAKN3LE2/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/NVTP4OYHCTRU3ONFJOFJQVNDFB25KLLG/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/YMAW7D2MP6RE4BFI5BZWOBBWGY3VSOFN/
- https://security.gentoo.org/glsa/202005-08
- https://www.debian.org/security/2020/dsa-4723
- https://xenbits.xen.org/xsa/advisory-314.html
