CVE-2021-47174

Service interruption via unsafe AVX2 softirq lookup

Published Mar 25, 2024 · Updated May 11, 2026

Denial of service in the Linux kernel allows local users to interrupt service through nftables PiPapo AVX2 lookups. The nft_pipapo_avx2_lookup function calls kernel FPU handling from softirq context without first checking irq_fpu_usable(), causing kernel_fpu_begin_mask to warn rather than selecting the scalar lookup. Reachability requires an x86 CPU with AVX2 and an nftables PiPapo set evaluated during a softirq; the published impact is limited to availability.

CVSS severity5.5
Medium
EPSS probability0.23%
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 the Linux kernel allows local users to interrupt service through nftables PiPapo AVX2 lookups. The nft_pipapo_avx2_lookup function calls kernel FPU handling from softirq context without first checking irq_fpu_usable(), causing kernel_fpu_begin_mask to warn rather than selecting the scalar lookup. Reachability requires an x86 CPU with AVX2 and an nftables PiPapo set evaluated during a softirq; the published impact is limited to availability.

The record

CVE
CVE-2021-47174
Published
Mar 25, 2024
Updated
May 11, 2026
Vendor
The Linux Kernel Organization
Product
Linux
Classifications
T1499
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Mar 25, 2024CVE publishedPublication date reported by the CVE source.
  2. May 11, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=5.7
  2. Affected versionversion=7400b063969bdca4a06cd97f1294d765c8eecbe1 <727a2b4fc951ee69847d4904d98961856ea9fbe6
  3. Affected versionversion=7400b063969bdca4a06cd97f1294d765c8eecbe1 <b1f45a26bd322525c14edd9504f6d46dfad679a4
  4. Affected versionversion=7400b063969bdca4a06cd97f1294d765c8eecbe1 <f0b3d338064e1fe7531f0d2977e35f3b334abfb4

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

The Linux Kernel Organization · Linuxversion=5.7; version=7400b063969bdca4a06cd97f1294d765c8eecbe1 <727a2b4fc951ee69847d4904d98961856ea9fbe6; version=7400b063969bdca4a06cd97f1294d765c8eecbe1 <b1f45a26bd322525c14edd9504f6d46dfad679a4; version=7400b063969bdca4a06cd97f1294d765c8eecbe1 <f0b3d338064e1fe7531f0d2977e35f3b334abfb4

Published CVSS scores

5.5UbuntuCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
5.5SUSECVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
5.5Amazon LinuxCVSS: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.

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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
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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