CVE-2021-47245Network attack vector

Unauthenticated host disruption via SYNPROXY option parsing

Published May 21, 2024 · Updated Aug 5, 2026

Out-of-bounds read in Linux kernel 3.12 through 5.13-rc6 allows remote attackers to disrupt hosts via crafted TCP options. When one byte remains and its opcode is neither EOL nor NOP, synproxy_parse_options reads a second byte past the TCP option boundary. The unauthenticated path is reachable only when SYNPROXY processes matching inbound packets; the invalid kernel read can fault the host or access one adjacent byte.

CVSS severity7.1
High
EPSS probability0.78%
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 Linux kernel 3.12 through 5.13-rc6 allows remote attackers to disrupt hosts via crafted TCP options. When one byte remains and its opcode is neither EOL nor NOP, synproxy_parse_options reads a second byte past the TCP option boundary. The unauthenticated path is reachable only when SYNPROXY processes matching inbound packets; the invalid kernel read can fault the host or access one adjacent byte.

The record

CVE
CVE-2021-47245
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

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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=3.12
  2. Affected versionversion=48b1de4c110a7afa4b85862f6c75af817db26fad <576c1526b4d83c44ad7b673cb841f36cbc6cb6c4
  3. Affected versionversion=48b1de4c110a7afa4b85862f6c75af817db26fad <5fc177ab759418c9537433e63301096e733fb915
  4. Affected versionversion=48b1de4c110a7afa4b85862f6c75af817db26fad <674b5f0c6a4fc5d3abce877048290cea6091fcb1
  5. Affected versionversion=48b1de4c110a7afa4b85862f6c75af817db26fad <6defc77d48eff74075b80ad5925061b2fc010d98
  6. Affected versionversion=48b1de4c110a7afa4b85862f6c75af817db26fad <7d9a9a1a88a3da574e019b4de756bc73337b3b0b
  7. Affected versionversion=48b1de4c110a7afa4b85862f6c75af817db26fad <9cdf299ba4e153b5e56187648420de22c6216f02
  8. Affected versionversion=48b1de4c110a7afa4b85862f6c75af817db26fad <e1eb98cfeafdd85537e7e3cefe93ca9bfbcc3ea8
  9. Affected versionversion=48b1de4c110a7afa4b85862f6c75af817db26fad <f648089337cb8ed40b2bb96e244f72b9d97dc96b

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

The Linux Kernel Organization · Linuxversion=3.12; version=48b1de4c110a7afa4b85862f6c75af817db26fad <576c1526b4d83c44ad7b673cb841f36cbc6cb6c4; version=48b1de4c110a7afa4b85862f6c75af817db26fad <5fc177ab759418c9537433e63301096e733fb915; version=48b1de4c110a7afa4b85862f6c75af817db26fad <674b5f0c6a4fc5d3abce877048290cea6091fcb1; version=48b1de4c110a7afa4b85862f6c75af817db26fad <6defc77d48eff74075b80ad5925061b2fc010d98; version=48b1de4c110a7afa4b85862f6c75af817db26fad <7d9a9a1a88a3da574e019b4de756bc73337b3b0b; version=48b1de4c110a7afa4b85862f6c75af817db26fad <9cdf299ba4e153b5e56187648420de22c6216f02; version=48b1de4c110a7afa4b85862f6c75af817db26fad <e1eb98cfeafdd85537e7e3cefe93ca9bfbcc3ea8; version=48b1de4c110a7afa4b85862f6c75af817db26fad <f648089337cb8ed40b2bb96e244f72b9d97dc96b

Published CVSS scores

7.1CanonicalCVSS: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.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

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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