CVE-2021-47185

System hang via non-yielding TTY buffer flush

Published Apr 10, 2024 · Updated May 11, 2026

Denial of service in the Linux kernel allows local users to hang a non-preemptible ARM64 system by rapidly writing to a PTY master. Concurrent writes keep the flush_to_ldisc workqueue draining buffers indefinitely because its loop does not yield when rescheduling is needed. Reaching the condition requires high local privileges, execution on separate cores, and a kernel built without preemption; the bounded consequence is a watchdog-detected soft lockup and system hang.

CVSS severity4.4
Medium
EPSS probability0.18%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Denial of service in the Linux kernel allows local users to hang a non-preemptible ARM64 system by rapidly writing to a PTY master. Concurrent writes keep the flush_to_ldisc workqueue draining buffers indefinitely because its loop does not yield when rescheduling is needed. Reaching the condition requires high local privileges, execution on separate cores, and a kernel built without preemption; the bounded consequence is a watchdog-detected soft lockup and system hang.

The record

CVE
CVE-2021-47185
Published
Apr 10, 2024
Updated
May 11, 2026
Vendor
The Linux Kernel Organization
Product
Linux
Classifications
CWE-667, T1499
Attack vector
local
Privileges
admin

Timeline

How it unfolded

  1. Apr 10, 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=3.0
  2. Affected versionversion=81de916f19cf5f1437c0b9ed817364f0f7c81961 <0380f643f3a7a61b0845cdc738959c2ad5735d61
  3. Affected versionversion=81de916f19cf5f1437c0b9ed817364f0f7c81961 <3968ddcf05fb4b9409cd1859feb06a5b0550a1c1
  4. Affected versionversion=81de916f19cf5f1437c0b9ed817364f0f7c81961 <4c1623651a0936ee197859824cdae6ebbd04d3ed
  5. Affected versionversion=81de916f19cf5f1437c0b9ed817364f0f7c81961 <4f300f47dbcf9c3d4b2ea76c8554c8f360400725
  6. Affected versionversion=81de916f19cf5f1437c0b9ed817364f0f7c81961 <5c34486f04700f1ba04907231dce0cc2705c2d7d
  7. Affected versionversion=81de916f19cf5f1437c0b9ed817364f0f7c81961 <77e9fed33056f2a88eba9dd4d2d5412f0c7d1f41
  8. Affected versionversion=81de916f19cf5f1437c0b9ed817364f0f7c81961 <b1ffc16ec05ae40d82b6e373322d62e9d6b54fbc
  9. Affected versionversion=81de916f19cf5f1437c0b9ed817364f0f7c81961 <d491c84df5c469dd9621863b6a770b3428137063

What conditions does exploitation require?

Attack vectorlocal
Required privilegesadmin

What is affected?

The Linux Kernel Organization · Linuxversion=3.0; version=81de916f19cf5f1437c0b9ed817364f0f7c81961 <0380f643f3a7a61b0845cdc738959c2ad5735d61; version=81de916f19cf5f1437c0b9ed817364f0f7c81961 <3968ddcf05fb4b9409cd1859feb06a5b0550a1c1; version=81de916f19cf5f1437c0b9ed817364f0f7c81961 <4c1623651a0936ee197859824cdae6ebbd04d3ed; version=81de916f19cf5f1437c0b9ed817364f0f7c81961 <4f300f47dbcf9c3d4b2ea76c8554c8f360400725; version=81de916f19cf5f1437c0b9ed817364f0f7c81961 <5c34486f04700f1ba04907231dce0cc2705c2d7d; version=81de916f19cf5f1437c0b9ed817364f0f7c81961 <77e9fed33056f2a88eba9dd4d2d5412f0c7d1f41; version=81de916f19cf5f1437c0b9ed817364f0f7c81961 <b1ffc16ec05ae40d82b6e373322d62e9d6b54fbc; version=81de916f19cf5f1437c0b9ed817364f0f7c81961 <d491c84df5c469dd9621863b6a770b3428137063

Published CVSS scores

4.4CISA-ADPCVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:N/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)
Vectorlocal
Privilegesadmin
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-667Improper Locking
T1499Endpoint Denial of Service

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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