CVE-2021-47242Network attack vector

Remote CPU hang via recursive MPTCP locking

Published May 21, 2024 · Updated Aug 5, 2026

Denial of service in Linux kernel MPTCP 5.11.12 through 5.12.12 allows remote attackers to hang a CPU via crafted DSS options. In subflow_error_report(), invalid MPTCP mapping handling re-acquires mptcp_data_lock while callers already hold it, leaving the receive softirq spinning on a recursive lock. An unauthenticated peer must complete an MPTCP connection to an enabled listening service; the demonstrated consequence is a sustained CPU soft lockup.

CVSS severity7.5
High
EPSS probability0.33%
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 Linux kernel MPTCP 5.11.12 through 5.12.12 allows remote attackers to hang a CPU via crafted DSS options. In subflow_error_report(), invalid MPTCP mapping handling re-acquires mptcp_data_lock while callers already hold it, leaving the receive softirq spinning on a recursive lock. An unauthenticated peer must complete an MPTCP connection to an enabled listening service; the demonstrated consequence is a sustained CPU soft lockup.

The record

CVE
CVE-2021-47242
Published
May 21, 2024
Updated
Aug 5, 2026
Vendor
The Linux Kernel Organization
Product
Linux
Classifications
CWE-667, T1499.004
Attack vector
network
Privileges
unauthenticated

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=15cc10453398c22f78f6c2b897119ecce5e5dd89 <27ef25c72373222aaa5fe7b5cd890ae9cfb89a8d
  2. Affected versionversion=15cc10453398c22f78f6c2b897119ecce5e5dd89 <499ada5073361c631f2a3c4a8aed44d53b6f82ec
  3. Affected versionversion=5.11.12 <5.12
  4. Affected versionversion=5.12
  5. Affected versionversion=c8ad65cb5051498b8a58be40499db9e930f0092e

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

The Linux Kernel Organization · Linuxversion=15cc10453398c22f78f6c2b897119ecce5e5dd89 <27ef25c72373222aaa5fe7b5cd890ae9cfb89a8d; version=15cc10453398c22f78f6c2b897119ecce5e5dd89 <499ada5073361c631f2a3c4a8aed44d53b6f82ec; version=5.11.12 <5.12; version=5.12; version=c8ad65cb5051498b8a58be40499db9e930f0092e
The Linux Kernel Organization · Linux Kernelversion=15cc10453398 <27ef25c72373; version=15cc10453398 <499ada507336; version=5.12

Published CVSS scores

7.5LinuxCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
7.8CISA-ADPCVSS:3.1/AV:L/AC:L/PR:N/UI:R/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)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-667Improper Locking
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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