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FedoraOperating system · Fedoraproject

CVE-2021-28705

HIGH · 7.8 CVSS v3.1 Published 2021-11-24
Fix available
A fix is available. Upgrade to after 4.14.3 or later.
See remediation →
80/100
Remediation priority · High
Zero-click Patch available

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
issues with partially successful P2M updates on x86 T[his CNA information record relates to multiple CVEs; the text explains which aspects/vulnerabilities correspond to which CVE.] x86 HVM and PVH guests may be started in populate-on-demand (PoD) mode, to provide a way for them to later easily have more memory assigned. Guests are permitted to control certain P2M aspects of individual pages via hypercalls. These hypercalls may act on ranges of pages specified via page orders (resulting in a power-of-2 number of pages). In some cases the hypervisor carries out the requests by splitting them into smaller chunks. Error handling in certain PoD cases has been insufficient in that in particular partial success of some operations was not properly accounted for. There are two code paths affected - page removal (CVE-2021-28705) and insertion of new pages (CVE-2021-28709). (We provide one patch which combines the fix to both issues.)

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

A detailed technical summary for this CVE is being prepared.

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:= 34= 35
Debian LinuxOperating system
Affected:= 11.0
XenOperating system
Affected:>= 3.4.0, <= 4.12.4>= 4.13.0, <= 4.13.4>= 4.14.0, <= 4.14.3= 4.15.0= 4.15.1

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
High
Integrity
High
Availability
High

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

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.

dbcve · scoped
Upgrade available Upgrade to a release after 4.14.3
Vendor patch xenbits.xenproject.org →
Recommended fix High confidence

Xen 4.15.1+ or Xen 4.14.4+ or Xen 4.13.5+ (latest stable release recommended)

  1. Identify the current Xen hypervisor version using 'xl version' or 'xm version'
  2. For Xen 4.15.0: Upgrade to Xen 4.15.1 or later stable release
  3. For Xen 4.14.x (up to 4.14.3): Upgrade to Xen 4.14.4 or later
  4. For Xen 4.13.x (up to 4.13.4): Upgrade to Xen 4.13.5 or later
  5. For Xen 4.12.x and earlier: Upgrade to the latest supported stable series (4.14.x or 4.15.x)
  6. After upgrading the hypervisor, ensure all running HVM/PVH guests are restarted to apply the fix to their memory management context
  7. Verify the fix is applied by checking Xen version output matches the fixed release
Caveat Guests must be rebooted after hypervisor upgrade for the fix to take effect; live migration may be needed for zero-downtime

Generated from the published advisory — verify against the referenced sources before acting.

We can identify the exact fixed release, upgrade, and verify it in staging — typical engagement from $1,950. Get the upgrade done

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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-2021-28705 in production — separate from our analysis above.

No notes yet

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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
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