CVE-2021-46936

Local kernel crash via TIME_WAIT timer use-after-free

Published Feb 27, 2024 · Updated Aug 5, 2026

Use-after-free in the Linux kernel allows local users to corrupt kernel memory and trigger a panic during network namespace teardown. The ipv4_mib_exit_net teardown frees net->mib.net_statistics before tcp_sk_exit_batch removes in-flight TCP TIME_WAIT timers, so tw_timer_handler later writes through freed memory. Exploitation requires low-privilege local namespace and socket operations; the demonstrated consequence is a kernel page-fault panic that interrupts the host.

CVSS severity7.8
High
EPSS probability0.25%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Use-after-free in the Linux kernel allows local users to corrupt kernel memory and trigger a panic during network namespace teardown. The ipv4_mib_exit_net teardown frees net->mib.net_statistics before tcp_sk_exit_batch removes in-flight TCP TIME_WAIT timers, so tw_timer_handler later writes through freed memory. Exploitation requires low-privilege local namespace and socket operations; the demonstrated consequence is a kernel page-fault panic that interrupts the host.

The record

CVE
CVE-2021-46936
Published
Feb 27, 2024
Updated
Aug 5, 2026
Vendor
The Linux Kernel Organization
Product
Linux
Classifications
CWE-416, T1499.004
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Feb 27, 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=2.6.27
  2. Affected versionversion=61a7e26028b94805fd686a6dc9dbd9941f8f19b0 <08eacbd141e2495d2fcdde84358a06c4f95cbb13
  3. Affected versionversion=61a7e26028b94805fd686a6dc9dbd9941f8f19b0 <15579e1301f856ad9385d720c9267c11032a5022
  4. Affected versionversion=61a7e26028b94805fd686a6dc9dbd9941f8f19b0 <2386e81a1d277f540e1285565c9d41d531bb69d4
  5. Affected versionversion=61a7e26028b94805fd686a6dc9dbd9941f8f19b0 <5c2fe20ad37ff56070ae0acb34152333976929b4
  6. Affected versionversion=61a7e26028b94805fd686a6dc9dbd9941f8f19b0 <a8e1944b44f94f5c5f530e434c5eaee787254566
  7. Affected versionversion=61a7e26028b94805fd686a6dc9dbd9941f8f19b0 <e22e45fc9e41bf9fcc1e92cfb78eb92786728ef0
  8. Affected versionversion=61a7e26028b94805fd686a6dc9dbd9941f8f19b0 <e73164e89d1be561228a4534e1091369ee4ba41a
  9. Affected versionversion=61a7e26028b94805fd686a6dc9dbd9941f8f19b0 <fe5838c22b986c1190f1dce9aa09bf6a491c1a69

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

The Linux Kernel Organization · Linuxversion=2.6.27; version=61a7e26028b94805fd686a6dc9dbd9941f8f19b0 <08eacbd141e2495d2fcdde84358a06c4f95cbb13; version=61a7e26028b94805fd686a6dc9dbd9941f8f19b0 <15579e1301f856ad9385d720c9267c11032a5022; version=61a7e26028b94805fd686a6dc9dbd9941f8f19b0 <2386e81a1d277f540e1285565c9d41d531bb69d4; version=61a7e26028b94805fd686a6dc9dbd9941f8f19b0 <5c2fe20ad37ff56070ae0acb34152333976929b4; version=61a7e26028b94805fd686a6dc9dbd9941f8f19b0 <a8e1944b44f94f5c5f530e434c5eaee787254566; version=61a7e26028b94805fd686a6dc9dbd9941f8f19b0 <e22e45fc9e41bf9fcc1e92cfb78eb92786728ef0; version=61a7e26028b94805fd686a6dc9dbd9941f8f19b0 <e73164e89d1be561228a4534e1091369ee4ba41a; version=61a7e26028b94805fd686a6dc9dbd9941f8f19b0 <fe5838c22b986c1190f1dce9aa09bf6a491c1a69

Published CVSS scores

7.8NISTCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
7.8LinuxCVSS: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-416Use After Free
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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