CVE-2021-47261

Local kernel panic via wrong CQ buffer

Published May 21, 2024 · Updated Aug 5, 2026

Improper initialization in Linux 4.17 through 5.13-rc5 allows local users to trigger a kernel panic by enlarging an mlx5 completion queue. init_cq_frag_buf calls get_cqe, which always reads cq->buf even while the temporary resize buffer is being initialized, so enlargement indexes beyond the current buffer. A local workload able to exercise mlx5 RDMA completion-queue resizing can crash the host kernel.

CVSS severity7.8
High
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

Improper initialization in Linux 4.17 through 5.13-rc5 allows local users to trigger a kernel panic by enlarging an mlx5 completion queue. init_cq_frag_buf calls get_cqe, which always reads cq->buf even while the temporary resize buffer is being initialized, so enlargement indexes beyond the current buffer. A local workload able to exercise mlx5 RDMA completion-queue resizing can crash the host kernel.

The record

CVE
CVE-2021-47261
Published
May 21, 2024
Updated
Aug 5, 2026
Vendor
The Linux Kernel Organization
Product
Linux
Classifications
CWE-706, T1499
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. May 21, 2024CVE publishedPublication date reported by the CVE source.
  2. Aug 5, 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=388ca8be00370db132464e27f745b8a0add19fcb <1ec2dcd680c71d0d36fa25638b327a468babd5c9
  2. Affected versionversion=388ca8be00370db132464e27f745b8a0add19fcb <2ba0aa2feebda680ecfc3c552e867cf4d1b05a3a
  3. Affected versionversion=388ca8be00370db132464e27f745b8a0add19fcb <3e670c54eda238cb8a1ea93538a79ae89285c1c4
  4. Affected versionversion=388ca8be00370db132464e27f745b8a0add19fcb <91f7fdc4cc10542ca1045c06aad23365f0d067e0
  5. Affected versionversion=388ca8be00370db132464e27f745b8a0add19fcb <e3ecd9c09fcc10cf6b2bc67e2990c397c40a8c26
  6. Affected versionversion=4.17

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

The Linux Kernel Organization · Linuxversion=388ca8be00370db132464e27f745b8a0add19fcb <1ec2dcd680c71d0d36fa25638b327a468babd5c9; version=388ca8be00370db132464e27f745b8a0add19fcb <2ba0aa2feebda680ecfc3c552e867cf4d1b05a3a; version=388ca8be00370db132464e27f745b8a0add19fcb <3e670c54eda238cb8a1ea93538a79ae89285c1c4; version=388ca8be00370db132464e27f745b8a0add19fcb <91f7fdc4cc10542ca1045c06aad23365f0d067e0; version=388ca8be00370db132464e27f745b8a0add19fcb <e3ecd9c09fcc10cf6b2bc67e2990c397c40a8c26; version=4.17

Published CVSS scores

7.8NIST NVDCVSS: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
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-706Use of Incorrectly-Resolved Name or Reference
T1499Endpoint Denial of Service

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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