CVE-2020-36557Public exploit

System crash via virtual-console deallocation race

Published Jul 21, 2022 · Updated Aug 4, 2024

Use-after-free in the Linux kernel before 5.6.2 allows local users to crash the system by racing virtual-console operations. The VT_DISALLOCATE ioctl treats a virtual console's vc_data structure as unused when its tty reference count reaches zero, although tty_release may still be closing it, so con_shutdown accesses freed memory. Exploitation requires local execution and precise concurrency between console deallocation and repeated tty open-and-close operations; the established consequence is a kernel crash.

CVSS severity5.1
Medium
EPSS probability0.20%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Use-after-free in the Linux kernel before 5.6.2 allows local users to crash the system by racing virtual-console operations. The VT_DISALLOCATE ioctl treats a virtual console's vc_data structure as unused when its tty reference count reaches zero, although tty_release may still be closing it, so con_shutdown accesses freed memory. Exploitation requires local execution and precise concurrency between console deallocation and repeated tty open-and-close operations; the established consequence is a kernel crash.

The record

CVE
CVE-2020-36557
Published
Jul 21, 2022
Updated
Aug 4, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-362, CWE-416, T1499.004
Attack vector
local
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jul 21, 2022CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectorlocal
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

5.1NIST NVDCVSS:3.1/AV:L/AC:H/PR:N/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
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-362Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition')
CWE-416Use After Free
T1499.004Application or System Exploitation

Public exploit references

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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