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NVD / CVE Program· CNA XEN

CVE-2021-28689: x86: Speculative vulnerabilities with bare (non-shim) 32-bit PV guests 32-bit x86 PV guest kernels run in ring 1.

Noroxi assessment

Priority: Monitor (action score 22/100)

  • The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
  • Probability of exploitation in the next 30 days: 0.36% (FIRST EPSS).
  • Someone with local access to the system can trigger it. A low-privileged account is enough. No user action is required. No special conditions are required; it is repeatable.
  • Fixed version: xen (openSUSE:Leap Micro 5.2) 4.14.5_06-150300.3.35.1; xen (SUSE:Linux Enterprise High Performance Computing 15 SP1-ESPOS) 4.12.4_30-150100.3.80.1; xen (SUSE:Linux Enterprise High Performance Computing 15 SP2-ESPOS) 4.13.4_16-150200.3.65.1.

Low priority for now. Upgrade to xen (openSUSE:Leap Micro 5.2) 4.14.5_06-150300.3.35.1; xen (SUSE:Linux Enterprise High Performance Computing 15 SP1-ESPOS) 4.12.4_30-150100.3.80.1; xen (SUSE:Linux Enterprise High Performance Computing 15 SP2-ESPOS) 4.13.4_16-150200.3.65.1 or later.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

x86: Speculative vulnerabilities with bare (non-shim) 32-bit PV guests 32-bit x86 PV guest kernels run in ring 1. At the time when Xen was developed, this area of the i386 architecture was rarely used, which is why Xen was able to use it to implement paravirtualisation, Xen's novel approach to virtualization. In AMD64, Xen had to use a different implementation approach, so Xen does not use ring 1 to support 64-bit guests. With the focus now being on 64-bit systems, and the availability of explicit hardware support for virtualization, fixing speculation issues in ring 1 is not a priority for processor companies. Indirect Branch Restricted Speculation (IBRS) is an architectural x86 extension put together to combat speculative execution sidechannel attacks, including Spectre v2. It was retrofitted in microcode to existing CPUs. For more details on Spectre v2, see: http://xenbits.xen.org/xsa/advisory-254.html However, IBRS does not architecturally protect ring 0 from predictions learnt in ring 1. For more details, see: https://software.intel.com/security-software-guidance/deep-dives/deep-dive-indirect-branch-restricted-speculation Similar situations may exist with other mitigations for other kinds of speculative execution attacks. The situation is quite likely to be similar for speculative execution attacks which have yet to be discovered, disclosed, or mitigated.

MediumCVSS 5.5 · v3.1—No exploit Fix available
Published
Jun 11, 2021
Updated
Jun 16, 2026
EPSS
0.3% · 29th percentile

Report tools

JSON

Action score

22

Monitor

Low priority for now.

CVSS
22 / 40 · 5.5 / 10
CISA KEV
0 / 30 · Not listed
EPSS
0 / 30 · 0.3%

Get told when this record changes

  • Not in KEV: no record of exploitation in the wild
  • No public exploit code on record
  • A fix has been released

If any of these changes, we'll tell you in the daily email digest.

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When you'll hear from us

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  • when exploit code appears or is weaponized
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  • when EPSS rises 20 points in a week

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Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

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Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

VendorProduct
xenxen

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

  • xen xenbefore 4.12.0

Versions reported by the vendor

Affected version ranges reported by the assigning authority (XEN). Independent of NVD's CPE analysis and usually ahead of it.

  • Xen Xen

    • unspecified and later · before 4.12unknown

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

EcosystemPackageAffected rangeFix
Debian:12xenfrom 0—
openSUSE:Leap Micro 5.2xenbefore 4.14.5_06-150300.3.35.14.14.5_06-150300.3.35.1
SUSE:Linux Enterprise High Performance Computing 15 SP1-ESPOSxenbefore 4.12.4_30-150100.3.80.14.12.4_30-150100.3.80.1
SUSE:Linux Enterprise High Performance Computing 15 SP2-ESPOSxenbefore 4.13.4_16-150200.3.65.14.13.4_16-150200.3.65.1
SUSE:Linux Enterprise High Performance Computing 15-ESPOSxenbefore 4.10.4_40-150000.3.84.14.10.4_40-150000.3.84.1
SUSE:Linux Enterprise Module for Basesystem 15 SP3xenbefore 4.14.5_06-150300.3.35.14.14.5_06-150300.3.35.1
SUSE:Linux Enterprise Server 12 SP2-BCLxenbefore 4.7.6_28-43.98.14.7.6_28-43.98.1
SUSE:Linux Enterprise Software Development Kit 12 SP5xenbefore 4.12.4_28-3.77.14.12.4_28-3.77.1
SUSE:OpenStack Cloud 9xenbefore 4.11.4_34-2.83.14.11.4_34-2.83.1
SUSE:OpenStack Cloud 9xenbefore 4.11.4_18-2.54.14.11.4_18-2.54.1

Same product

xen: all records

Other highest-scoring records for the same primary product.

  • CVE-2017-10921The grant-table feature in Xen through 4.8.x does not ensure sufficient type counts for a GNTMAP_device_map and GNTMAP_host_map mapping, whi
    41Plan
  • CVE-2017-10920The grant-table feature in Xen through 4.8.x mishandles a GNTMAP_device_map and GNTMAP_host_map mapping, when followed by only a GNTMAP_host
    41Plan
  • CVE-2017-10918Xen through 4.8.x does not validate memory allocations during certain P2M operations, which allows guest OS users to obtain privileged host
    41Plan

Published before and after this one in the same product

  • ← EarlierCVE-2021-26314Jun 9, 2021 · AMD Speculative execution with Floating-Point Value Injection
    22Monitor
  • ← EarlierCVE-2021-28687Jun 11, 2021 · HVM soft-reset crashes toolstack libxl requires all data structures passed across its public interface to be initialized before use and disp
    22Monitor
  • Later →CVE-2021-28690Jun 29, 2021 · x86: TSX Async Abort protections not restored after S3 This issue relates to the TSX Async Abort speculative security vulnerability.
    26Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / packageFixed versionSource
opensuse:xen4.14.5_06-150300.3.35.1 · openSUSE:Leap Micro 5.2Package registry (OSV)
suse:xen4.11.4_18-2.54.1 · SUSE:OpenStack Cloud 9Package registry (OSV)
suse:xen4.14.5_06-150300.3.35.1 · SUSE:Linux Enterprise Module for Basesystem 15 SP3Package registry (OSV)

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

No dated events beyond publication.

No history yet (it accumulates with the daily EPSS job).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

No commit or PR link among the references.

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

No nightly-computed relations.

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

—

Bug bounty scope

No known public program.

Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).

Technical details

Attack conditions

  • Someone with local access to the system can trigger it.
  • A low-privileged account is enough.
  • No user action is required.
  • No special conditions are required; it is repeatable.

If successful

Confidentiality
high · data can be read
Integrity
none
Availability
none
Attack vector
Local
Attack complexity
Low
Privileges required
Low
User interaction
None
Scope
Unchanged
Confidentiality impact
High
Integrity impact
None
Availability impact
None

Weakness class (CWE)

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

CVSS vector

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

nvd-primary

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

ATT&CK techniques

—

Change log

  1. Fix✗ → ✓

For records you follow, these changes also arrive as notifications. →

References

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records