dbcve.org
FedoraOperating system · Fedoraproject

CVE-2020-25600

MEDIUM · 5.5 CVSS v3.1 Published 2020-09-23
Fix available
A fix is available. Upgrade to after 4.14.0 or later.
See remediation →
57/100
Remediation priority · Elevated
Zero-click

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 · unedited
An issue was discovered in Xen through 4.14.x. Out of bounds event channels are available to 32-bit x86 domains. The so called 2-level event channel model imposes different limits on the number of usable event channels for 32-bit x86 domains vs 64-bit or Arm (either bitness) ones. 32-bit x86 domains can use only 1023 channels, due to limited space in their shared (between guest and Xen) information structure, whereas all other domains can use up to 4095 in this model. The recording of the respective limit during domain initialization, however, has occurred at a time where domains are still deemed to be 64-bit ones, prior to actually honoring respective domain properties. At the point domains get recognized as 32-bit ones, the limit didn't get updated accordingly. Due to this misbehavior in Xen, 32-bit domains (including Domain 0) servicing other domains may observe event channel allocations to succeed when they should really fail. Subsequent use of such event channels would then possibly lead to corruption of other parts of the shared info structure. An unprivileged guest may cause another domain, in particular Domain 0, to misbehave. This may lead to a Denial of Service (DoS) for the entire system. All Xen versions from 4.4 onwards are vulnerable. Xen versions 4.3 and earlier are not vulnerable. Only x86 32-bit domains servicing other domains are vulnerable. Arm systems, as well as x86 64-bit domains, are not vulnerable.

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 · high confidence

In Xen 4.4+, the event channel limit for 32-bit x86 domains was recorded before the domain type was correctly identified, causing these domains to receive the 4095-channel limit instead of the correct 1023-channel limit. This allows event channel allocations to succeed when they should fail, leading to corruption of the shared info structure between guest and hypervisor. An unprivileged guest can trigger this in Domain 0 or other 32-bit domains, causing system-wide DoS.

MitigationUpgrade to a patched Xen version. If immediate patching is not possible, avoid running untrusted 32-bit x86 paravirtualized guests and consider restricting 32-bit domain usage to trusted workloads only.

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
FedoraOperating system
Affected:= 31= 32= 33
Debian LinuxOperating system
Affected:= 10.0
XenOperating system
Affected:>= 4.4.0, <= 4.14.0
LeapOperating system
Affected:= 15.2

CVSS 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
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/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 checks

Work through these to decide whether this CVE applies to you.

  1. Identify installed Xen version
    Run 'xl info' or 'xm info' to display hypervisor version information, or check /sys/hypervisor/version if available
    Affected if Version is 4.4.0 through 4.14.0 inclusive
  2. Determine if 32-bit x86 domains are running
    Execute 'xl list' to enumerate active domains and check their bitness, or query domain configuration files for arch type
    Affected if Any 32-bit x86 paravirtualized domain (domU or dom0) is active
  3. Check for Domain 0 architecture
    Run 'uname -a' within Domain 0 to verify if it is a 32-bit kernel, or check dom0 kernel package version
    Affected if Domain 0 is running a 32-bit x86 kernel
  4. Inspect event channel allocation
    Monitor Xen event channel usage via 'xl debugs keys' or check /proc/xen for channel allocations in guest domains
    Affected if Event channel allocations succeed beyond expected 1023 limit for 32-bit domains
  5. Review shared info structure integrity
    Check Xen logs (xm dmesg or journalctl for xen domain messages) for corruption warnings or failures related to shared info pages
    Affected if Errors appear indicating shared info structure corruption or unexpected event channel behavior in 32-bit domains

You are affected if running Xen version 4.4.0-4.14.0 with any active 32-bit x86 domain (including dom0 as 32-bit) where event channels exceed the intended 1023 limit.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

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 data
Upgrade available Upgrade to a release after 4.14.0
Interim mitigation

Upgrade to a patched Xen version. If immediate patching is not possible, avoid running untrusted 32-bit x86 paravirtualized guests and consider restricting 32-bit domain usage to trusted workloads only.

Fix this in Fedora Scoped from the published advisory
  • Consultation4.0 h
  • Implementation8.0 h
  • Testing12.0 h
  • Review / QA4.0 h
28.0 hours of engineering $4,760
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $7,616.

Scan for this in your stack

Free · runs locally
dbcve dependency scanner

Check whether your project pulls in CVE-2020-25600 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.

Get it on GitHub Scan in the browser

References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2020-25600 in production — separate from our analysis above.

No notes yet

Be the first to add a field note for this CVE — a mitigation you’ve verified, a version caveat, or a link to a working fix. Sign in above to contribute.

What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • 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
  • No spam, self-promotion, credentials, or personal data