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CVE Record

CVE-2021-46968: s390/zcrypt: fix zcard and zqueue hot-unplug memleak

In the Linux kernel, the following vulnerability has been resolved: s390/zcrypt: fix zcard and zqueue hot-unplug memleak Tests with kvm and a kmemdebug kernel showed, that on hot unplug the zcard and zqueue structs for the unplugged card or queue are not properly freed because of a mismatch with get/put for the embedded kref counter. This fix now adjusts the handling of the kref counters. With init the kref counter starts with 1. This initial value needs to drop to zero with the unregister of the card or queue to trigger the release and free the object.

UnknownCVSS not scoredNot KEV-listedUpdated
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Glexia's TakeAutomated analysisunknown

Security readout for executives and security teams

Plain-English summary

This Linux kernel issue affects the s390 zcrypt crypto-device hot-unplug path. When a crypto card or queue is removed, kernel objects may not be freed correctly, creating a memory leak. The business risk appears narrow and availability-oriented, but the source provides no CVSS score or confirmed exploitation.

Executive priority

Handle through normal kernel patch management unless the organization operates IBM Z or s390 Linux systems with zcrypt hot-unplug workflows. For those environments, prioritize validation and patching to reduce avoidable availability risk.

Technical view

The bug is a kref get/put mismatch for embedded reference counters in zcard and zqueue structures. On hot unplug, unregister should drop the initial kref to zero so release frees the object. The kernel fix adjusts reference-count handling for cards and queues.

Likely exposure

Exposure appears limited to Linux systems using the s390/zcrypt subsystem, especially environments with crypto card or queue hot-unplug activity. Non-s390 Linux hosts are not indicated as affected by the provided sources.

Exploitation context

The provided sources do not report active exploitation, public exploit availability, or KEV listing. The described condition requires the relevant s390 zcrypt hot-unplug code path and results in leaked kernel memory objects.

Researcher notes

Evidence is limited to the CVE record and Linux stable commit references. No CVSS, CWE, exploit status, or detailed impact analysis is provided. Treat remediation mapping through distribution backports carefully rather than relying only on upstream version labels.

Mitigation direction

  • Update to a Linux kernel containing the referenced stable zcrypt fixes.
  • Prioritize s390 systems using zcrypt cards or queues.
  • Check Linux distribution advisories for backported fixed packages.
  • Minimize unnecessary zcrypt card or queue hot-unplug activity until patched.

Validation and detection

  • Inventory Linux hosts running on s390 architecture.
  • Identify systems using the zcrypt subsystem or crypto adapter queues.
  • Compare deployed kernel versions with vendor fixed-package guidance.
  • Review maintenance logs for zcrypt card or queue hot-unplug activity.
Prepared
Confidence
medium
Sources
6

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

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ATT&CK lookup starting points

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CVE-2021-46968 mapping review

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Vulnerability profileCVE Program record
Severity
Unknown
CVSS
Not scored
Known Exploited
No
Published
Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

0CVSS vectors
3Timeline events
2ADP providers
5Source links

SSVC decision data

CISA-ADPCISA Coordinator
Timestamp
Version
2.0.3
Exploitation: noneAutomatable: noTechnical Impact: partial

Vulnerability timeline

Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.

  1. CVE reservedCVE Program

    The CVE ID was reserved by the assigning CNA.

  2. CVE publishedCVE Program

    The CVE record was published.

  3. CVE updatedCVE Program

    The CVE record metadata indicates this as the latest update time.

ADP provider summaries

CVECVE Program Container
CISA-ADPCISA ADP Vulnrichment
other:ssvc

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
LinuxLinux29c2680fd2bf3862ff5cf2957f198512493156f9, 29c2680fd2bf3862ff5cf2957f198512493156f9, 29c2680fd2bf3862ff5cf2957f198512493156f9, 29c2680fd2bf3862ff5cf2957f198512493156f9unaffected
LinuxLinux5.10, 0, 5.10.36, 5.11.20, 5.12.3, 5.13affected
Weakness

CWE details

No CWE listed

CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.