CVE-2021-47243

Out-of-bounds read via malformed TCP options

Published May 21, 2024 · Updated Aug 5, 2026

Out-of-bounds read in the sch_cake qdisc in Linux allows local users to trigger a one-byte over-read via malformed TCP options. When an option has length one and its opcode is neither EOL nor NOP, cake_get_tcpopt and cake_tcph_may_drop read a second byte beyond that option; cake_get_tcphdr also accepted TCP header lengths below five. Reachability requires CAKE to parse the malformed packet, and the published record does not demonstrate direct disclosure or a crash from the over-read.

CVSS severity7.1
High
EPSS probability0.26%
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 sch_cake qdisc in Linux allows local users to trigger a one-byte over-read via malformed TCP options. When an option has length one and its opcode is neither EOL nor NOP, cake_get_tcpopt and cake_tcph_may_drop read a second byte beyond that option; cake_get_tcphdr also accepted TCP header lengths below five. Reachability requires CAKE to parse the malformed packet, and the published record does not demonstrate direct disclosure or a crash from the over-read.

The record

CVE
CVE-2021-47243
Published
May 21, 2024
Updated
Aug 5, 2026
Vendor
The Linux Kernel Organization
Product
Linux
Classifications
CWE-125
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=4.19
  2. Affected versionversion=8b7138814f29933898ecd31dfc83e35a30ee69f5 <3371392c60e2685af30bd4547badd880f5df2b3f
  3. Affected versionversion=8b7138814f29933898ecd31dfc83e35a30ee69f5 <3b491dd593d582ceeb27aa617600712a6bd14246
  4. Affected versionversion=8b7138814f29933898ecd31dfc83e35a30ee69f5 <4cefa061fc63f4d2dff5ab4083f43857cd7a2335
  5. Affected versionversion=8b7138814f29933898ecd31dfc83e35a30ee69f5 <595897ef118d6fe66690c4fc5b572028c9da95b7
  6. Affected versionversion=8b7138814f29933898ecd31dfc83e35a30ee69f5 <ba91c49dedbde758ba0b72f57ac90b06ddf8e548

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

The Linux Kernel Organization · Linuxversion=4.19; version=8b7138814f29933898ecd31dfc83e35a30ee69f5 <3371392c60e2685af30bd4547badd880f5df2b3f; version=8b7138814f29933898ecd31dfc83e35a30ee69f5 <3b491dd593d582ceeb27aa617600712a6bd14246; version=8b7138814f29933898ecd31dfc83e35a30ee69f5 <4cefa061fc63f4d2dff5ab4083f43857cd7a2335; version=8b7138814f29933898ecd31dfc83e35a30ee69f5 <595897ef118d6fe66690c4fc5b572028c9da95b7; version=8b7138814f29933898ecd31dfc83e35a30ee69f5 <ba91c49dedbde758ba0b72f57ac90b06ddf8e548

Published CVSS scores

7.1kernel.orgCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/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 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-125Out-of-bounds Read

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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