CVE-2021-28689

Host memory disclosure via ring 1 predictions

Published Jun 11, 2021 · Updated Aug 3, 2024

Information disclosure in Xen on x86 allows guest OS users to infer arbitrary host memory through a bare 32-bit PV guest. IBRS leaves ring 0 exposed to predictions learned in ring 1, allowing speculative execution to expose data across the guest-hypervisor boundary. Exploitation requires a Spectre v2-susceptible CPU and a 32-bit PV guest running without PV-Shim; host and cross-guest memory are exposed.

CVSS severity5.5
Medium
EPSS probability0.36%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Information disclosure in Xen on x86 allows guest OS users to infer arbitrary host memory through a bare 32-bit PV guest. IBRS leaves ring 0 exposed to predictions learned in ring 1, allowing speculative execution to expose data across the guest-hypervisor boundary. Exploitation requires a Spectre v2-susceptible CPU and a 32-bit PV guest running without PV-Shim; host and cross-guest memory are exposed.

The record

CVE
CVE-2021-28689
Published
Jun 11, 2021
Updated
Aug 3, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-212
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Jun 11, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

5.5NIST NVDCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N
2.1NIST NVDAV:L/AC:L/Au:N/C:P/I:N/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-212Improper Removal of Sensitive Information Before Storage or Transfer

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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