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CVE Record

CVE-2021-28697: grant table v2 status pages may remain accessible after de-allocation Guest get permitted access to certain...

grant table v2 status pages may remain accessible after de-allocation Guest get permitted access to certain Xen-owned pages of memory. The majority of such pages remain allocated / associated with a guest for its entire lifetime. Grant table v2 status pages, however, get de-allocated when a guest switched (back) from v2 to v1. The freeing of such pages requires that the hypervisor know where in the guest these pages were mapped. The hypervisor tracks only one use within guest space, but racing requests from the guest to insert mappings of these pages may result in any of them to become mapped in multiple locations. Upon switching back from v2 to v1, the guest would then retain access to a page that was freed and perhaps re-used for other purposes.

UnknownCVSS not scoredNot KEV-listedUpdated
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Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

A Xen guest may keep access to memory pages after they should have been released. In environments where guests are untrusted or multi-tenant, this weakens hypervisor isolation and could expose Xen-owned memory if pages are later reused.

Executive priority

Treat as urgent for shared Xen infrastructure because it affects guest-to-hypervisor memory isolation. For single-tenant or trusted-guest environments, prioritize through normal hypervisor patch cycles after confirming version exposure.

Technical view

The issue affects Xen grant table v2 status pages. A race during guest mapping requests can create multiple mappings, while Xen tracks only one. When a guest switches from grant table v2 back to v1, Xen may free the page while a guest mapping remains accessible.

Likely exposure

Exposure is limited to Xen deployments using affected versions, especially hosts running untrusted guests. The bundle lists Xen xen-unstable, 4.11.x, 4.13.x, 4.15.x, and unspecified next 4.12.x/4.14.x versions.

Exploitation context

The provided sources do not show known active exploitation, and KEV status is false. Exploitation would require a guest able to exercise the relevant Xen grant table behavior and race condition.

Researcher notes

Evidence is strongest for the vulnerable condition and affected Xen branches, but the bundle lacks CVSS, CWE, exploit details, and named workarounds. Validate against XSA-379 and downstream package advisories before declaring exposure closed.

Mitigation direction

  • Review Xen XSA-379 and distribution advisories for fixed Xen packages.
  • Prioritize patching Xen hosts that run untrusted or multi-tenant guests.
  • Check Debian, Fedora, and Gentoo guidance if using their Xen packages.
  • Avoid relying on unverified workarounds; use vendor guidance.

Validation and detection

  • Inventory Xen hypervisor versions across virtualization hosts.
  • Identify hosts running untrusted, customer, or externally managed guests.
  • Confirm whether installed Xen packages include XSA-379 fixes.
  • Review change records for grant table version configuration exposure.
Prepared
Confidence
medium
Sources
6

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.

ATT&CK lookup starting points

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CVE-2021-28697 mapping review

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Vulnerability profileCVE Program record
Severity
Unknown
CVSS
Not scored
Known Exploited
No
Published
Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

0CVSS vectors
0Timeline events
0ADP providers
7Source links

CVSS and timeline data

No CVSS vectors or timeline events were available in the normalized CVE source material.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
Xenxenxen-unstableListed
Xenxenunspecified, 4.13.x, next of 4.14.xListed
Xenxenunspecified, 4.11.x, next of 4.12.xListed
Xenxen4.15.xListed
Weakness

CWE details

No CWE listed

CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.