CVE-2021-3308

Host denial of service via interrupt-vector leaks

Published Jan 26, 2021 · Updated Aug 3, 2024

Denial of service in Xen 4.12.3 through 4.12.4 and 4.13.1 through 4.14.x allows guest OS users to exhaust host interrupt vectors. During an HVM guest reboot, Xen fails to release IDT vectors assigned to enabled MSI or MSI-X entries, so repeated reboots consume the finite vector pool. The path requires an x86 HVM guest with a passed-through PCI device; exhaustion prevents PCI passthrough for other guests or the hardware domain and can interrupt the entire host.

CVSS severity5.5
Medium
EPSS probability0.42%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Denial of service in Xen 4.12.3 through 4.12.4 and 4.13.1 through 4.14.x allows guest OS users to exhaust host interrupt vectors. During an HVM guest reboot, Xen fails to release IDT vectors assigned to enabled MSI or MSI-X entries, so repeated reboots consume the finite vector pool. The path requires an x86 HVM guest with a passed-through PCI device; exhaustion prevents PCI passthrough for other guests or the hardware domain and can interrupt the entire host.

The record

CVE
CVE-2021-3308
Published
Jan 26, 2021
Updated
Aug 3, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
T1499
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Jan 26, 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

4.9NIST NVDAV:L/AC:L/Au:N/C:N/I:N/A:C
5.5NIST NVDCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

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

T1499Endpoint Denial of Service

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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