CVE-2021-47244Network attack vector

Remote kernel crash via malformed TCP options

Published May 21, 2024 · Updated Aug 5, 2026

Out-of-bounds read in the Linux kernel MPTCP parser allows remote attackers to crash affected hosts via crafted TCP options. In mptcp_get_options, a one-byte remainder containing neither EOL nor NOP is treated as if a length byte remains, causing a read past the validated TCP options area. Reachability requires an MPTCP listener or established MPTCP connection; the defect reads one byte and provides no memory-write primitive.

CVSS severity8.2
High
EPSS probability0.71%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Out-of-bounds read in the Linux kernel MPTCP parser allows remote attackers to crash affected hosts via crafted TCP options. In mptcp_get_options, a one-byte remainder containing neither EOL nor NOP is treated as if a length byte remains, causing a read past the validated TCP options area. Reachability requires an MPTCP listener or established MPTCP connection; the defect reads one byte and provides no memory-write primitive.

The record

CVE
CVE-2021-47244
Published
May 21, 2024
Updated
Aug 5, 2026
Vendor
The Linux Kernel Organization
Product
Linux
Classifications
CWE-125, T1499
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

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

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

  1. Affected versionversion=5.6
  2. Affected versionversion=cec37a6e41aae7bf3df9a3da783380a4d9325fd8 <07718be265680dcf496347d475ce1a5442f55ad7
  3. Affected versionversion=cec37a6e41aae7bf3df9a3da783380a4d9325fd8 <73eeba71dc9932970befa009e68272a3d5ec4a58
  4. Affected versionversion=cec37a6e41aae7bf3df9a3da783380a4d9325fd8 <76e02b8905d0691e89e104a882f3bba7dd0f6037

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

The Linux Kernel Organization · Linuxversion=5.6; version=cec37a6e41aae7bf3df9a3da783380a4d9325fd8 <07718be265680dcf496347d475ce1a5442f55ad7; version=cec37a6e41aae7bf3df9a3da783380a4d9325fd8 <73eeba71dc9932970befa009e68272a3d5ec4a58; version=cec37a6e41aae7bf3df9a3da783380a4d9325fd8 <76e02b8905d0691e89e104a882f3bba7dd0f6037

Published CVSS scores

8.2Linux CNACVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/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)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-125Out-of-bounds Read
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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