CVE-2021-47336

Memory exhaustion via oversized CIPSO rule

Published May 21, 2024 · Updated May 11, 2026

Resource exhaustion in the Linux kernel Smack module allows local users with CAP_MAC_ADMIN to exhaust memory via an oversized CIPSO rule. The smk_set_cipso function limited byte counts only for the legacy fixed-width format, so cipso2 passed an arbitrary count to memdup_user_nul before parsing one rule. Exploitation requires Smack to be enabled, smackfs to be mounted, and CAP_MAC_ADMIN; memory exhaustion can interrupt the host.

CVSS severity7.8
High
EPSS probability0.25%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Resource exhaustion in the Linux kernel Smack module allows local users with CAP_MAC_ADMIN to exhaust memory via an oversized CIPSO rule. The smk_set_cipso function limited byte counts only for the legacy fixed-width format, so cipso2 passed an arbitrary count to memdup_user_nul before parsing one rule. Exploitation requires Smack to be enabled, smackfs to be mounted, and CAP_MAC_ADMIN; memory exhaustion can interrupt the host.

The record

CVE
CVE-2021-47336
Published
May 21, 2024
Updated
May 11, 2026
Vendor
The Linux Kernel Organization
Product
Linux
Classifications
T1499
Attack vector
local
Privileges
admin

Timeline

How it unfolded

  1. May 21, 2024CVE publishedPublication date reported by the CVE source.
  2. May 11, 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=3.5
  2. Affected versionversion=f7112e6c9abf1c70f001dcf097c1d6e218a93f5c <135122f174c357b7a3e58f40fa5792156c5e93e6
  3. Affected versionversion=f7112e6c9abf1c70f001dcf097c1d6e218a93f5c <258fd821f69378453c071b9dd767b298810fc766
  4. Affected versionversion=f7112e6c9abf1c70f001dcf097c1d6e218a93f5c <3780348c1a0e14ffefcaf1fc521f815bcaac94b0
  5. Affected versionversion=f7112e6c9abf1c70f001dcf097c1d6e218a93f5c <49ec114a6e62d8d320037ce71c1aaf9650b3cafd
  6. Affected versionversion=f7112e6c9abf1c70f001dcf097c1d6e218a93f5c <5c2dca9a7a7ff6a2df34158903515e2e4fd3d2b2
  7. Affected versionversion=f7112e6c9abf1c70f001dcf097c1d6e218a93f5c <5f9880403e6b71d56924748ba331daf836243fca
  8. Affected versionversion=f7112e6c9abf1c70f001dcf097c1d6e218a93f5c <8f5c773a2871cf446e3f36b2834fb25bbb28512b
  9. Affected versionversion=f7112e6c9abf1c70f001dcf097c1d6e218a93f5c <cbd87ba6a13891acf6180783f8234a8b7a3e3d4d

What conditions does exploitation require?

Attack vectorlocal
Required privilegesadmin

What is affected?

The Linux Kernel Organization · Linuxversion=3.5; version=f7112e6c9abf1c70f001dcf097c1d6e218a93f5c <135122f174c357b7a3e58f40fa5792156c5e93e6; version=f7112e6c9abf1c70f001dcf097c1d6e218a93f5c <258fd821f69378453c071b9dd767b298810fc766; version=f7112e6c9abf1c70f001dcf097c1d6e218a93f5c <3780348c1a0e14ffefcaf1fc521f815bcaac94b0; version=f7112e6c9abf1c70f001dcf097c1d6e218a93f5c <49ec114a6e62d8d320037ce71c1aaf9650b3cafd; version=f7112e6c9abf1c70f001dcf097c1d6e218a93f5c <5c2dca9a7a7ff6a2df34158903515e2e4fd3d2b2; version=f7112e6c9abf1c70f001dcf097c1d6e218a93f5c <5f9880403e6b71d56924748ba331daf836243fca; version=f7112e6c9abf1c70f001dcf097c1d6e218a93f5c <8f5c773a2871cf446e3f36b2834fb25bbb28512b; version=f7112e6c9abf1c70f001dcf097c1d6e218a93f5c <cbd87ba6a13891acf6180783f8234a8b7a3e3d4d

Published CVSS scores

7.8SUSECVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
7.8UbuntuCVSS: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 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesadmin
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

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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