CVE-2021-26930

Host denial of service via blkback mapping errors

Published Feb 17, 2021 · Updated Aug 3, 2024

Improper error handling in Linux kernel 3.11 through 5.10.16 allows guest OS users to crash a Xen block backend via frontend requests. The grant-mapping path in drivers/block/xen-blkback/blkback.c can discard an earlier mapping error after later processing succeeds and can leave recovery state incomplete. A malicious or buggy paravirtualized block frontend is required; the crash affects its backend domain and becomes host-wide without driver-domain isolation.

CVSS severity7.8
High
EPSS probability0.35%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper error handling in Linux kernel 3.11 through 5.10.16 allows guest OS users to crash a Xen block backend via frontend requests. The grant-mapping path in drivers/block/xen-blkback/blkback.c can discard an earlier mapping error after later processing succeeds and can leave recovery state incomplete. A malicious or buggy paravirtualized block frontend is required; the crash affects its backend domain and becomes host-wide without driver-domain isolation.

The record

CVE
CVE-2021-26930
Published
Feb 17, 2021
Updated
Aug 3, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
T1499.004
Attack vector
local
Privileges
Unavailable

Timeline

How it unfolded

  1. Feb 17, 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 privilegesUnavailable in this record.

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

4.6NVDAV:L/AC:L/Au:N/C:P/I:P/A:P
7.8NVDCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/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.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
PrivilegesUnavailable
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

T1499.004Application or System Exploitation

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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