CVE-2021-47496Network attack vector

Kernel memory corruption via flipped KTLS error sign

Published May 22, 2024 · Updated Aug 5, 2026

Out-of-bounds write in Linux KTLS allows remote attackers to corrupt kernel memory through a malformed TLS record during splice transmission. tls_err_abort stores a negative crypto error in sk_err, causing tls_sw_do_sendpage to return a positive byte count that underflows pipe-buffer lengths and offsets. Reachability requires a KTLS service using the sendfile or splice path; the resulting bogus addresses allow kernel disclosure, writes, or a crash.

CVSS severity9.8
Critical
EPSS probability0.48%
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 write in Linux KTLS allows remote attackers to corrupt kernel memory through a malformed TLS record during splice transmission. tls_err_abort stores a negative crypto error in sk_err, causing tls_sw_do_sendpage to return a positive byte count that underflows pipe-buffer lengths and offsets. Reachability requires a KTLS service using the sendfile or splice path; the resulting bogus addresses allow kernel disclosure, writes, or a crash.

The record

CVE
CVE-2021-47496
Published
May 22, 2024
Updated
Aug 5, 2026
Vendor
The Linux Kernel Organization
Product
Linux
Classifications
CWE-787, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. May 22, 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=4.17
  2. Affected versionversion=c46234ebb4d1eee5e09819f49169e51cfc6eb909 <da353fac65fede6b8b4cfe207f0d9408e3121105
  3. Affected versionversion=c46234ebb4d1eee5e09819f49169e51cfc6eb909 <e0cfd5159f314d6b304d030363650b06a2299cbb
  4. Affected versionversion=c46234ebb4d1eee5e09819f49169e51cfc6eb909 <e41473543f75f7dbc5d605007e6f883f1bd13b9a
  5. Affected versionversion=c46234ebb4d1eee5e09819f49169e51cfc6eb909 <f3dec7e7ace38224f82cf83f0049159d067c2e19

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

The Linux Kernel Organization · Linuxversion=4.17; version=c46234ebb4d1eee5e09819f49169e51cfc6eb909 <da353fac65fede6b8b4cfe207f0d9408e3121105; version=c46234ebb4d1eee5e09819f49169e51cfc6eb909 <e0cfd5159f314d6b304d030363650b06a2299cbb; version=c46234ebb4d1eee5e09819f49169e51cfc6eb909 <e41473543f75f7dbc5d605007e6f883f1bd13b9a; version=c46234ebb4d1eee5e09819f49169e51cfc6eb909 <f3dec7e7ace38224f82cf83f0049159d067c2e19

Published CVSS scores

9.8Linux Kernel CNACVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
7.8NIST NVDCVSS: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)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-787Out-of-bounds Write
T1190Exploit Public-Facing Application

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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