CVE-2020-29040
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedAn issue was discovered in Xen through 4.14.x allowing x86 HVM guest OS users to cause a denial of service (stack corruption), cause a data leak, or possibly gain privileges because of an off-by-one error. NOTE: this issue is caused by an incorrect fix for CVE-2020-27671.
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysis · moderate confidenceXen hypervisor through 4.14.x contains an off-by-one error in x86 HVM (Hardware Virtual Machine) guest handling code that allows malicious or compromised HVM guest OS users to cause stack corruption (denial of service), leak sensitive data from host or other guests, or potentially escalate privileges to hypervisor level. This vulnerability is a regression caused by an incorrect fix for the earlier CVE-2020-27671.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.
NVD · CPE data<= 4.14.0CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Local
- Complexity
- Low
- Privileges
- Low
- User interaction
- None
- Scope
- Changed
- Confidentiality
- High
- Integrity
- High
- Availability
- High
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H
Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.
dbcve checksWork through these to decide whether this CVE applies to you.
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Identify Xen hypervisor installation and versionRun 'xl version' or 'xm version' to display the Xen hypervisor version. Alternatively, check /etc/xen/xen-command-line or 'dmesg | grep Xen' for version information.Affected if The displayed version is 4.14.x or lower (including 4.14.0)
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Confirm hypervisor roleVerify this system is functioning as a Xen hypervisor host by checking for Xen-specific processes (xl, xend) or checking /proc/xen for hypervisor presence.Affected if The system is confirmed as a Xen hypervisor host running version 4.14.x or lower
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Check for active HVM guestsRun 'xl list' or 'virsh list --all' to list all virtual machines. Look for guests with type 'hvm' or 'HVM' in their configuration.Affected if Any HVM-type virtual machines are running on this hypervisor
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Verify HVM guest configuration is in useExamine guest configuration files in /etc/xen/ or via 'xl cfg' commands to confirm HVM (Hardware Virtual Machine) mode is enabled for any guests, not just PV (Paravirtual) guests.Affected if HVM guest mode is enabled or configured on any guest VM
You are affected if this system is a Xen hypervisor host running version 4.14.0 or any 4.14.x version AND has HVM guests configured or running.
Generated from the published advisory. Verify against your own configuration.
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
From vendor dataApply the corrected Xen security patch to all hypervisor hosts. This is a hypervisor-level vulnerability requiring Xen update; ensure proper testing of HVM guest functionality after patching.
- Consultation4.0 h
- Implementation8.0 h
- Testing10.0 h
- Review / QA4.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $7,136.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2020-29040 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2020-29040 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- Verified mitigations, workarounds, and config changes
- Version or environment caveats, and links to real fixes
- No weaponised exploit code, or anything meant to cause harm
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