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CVE Record

CVE-2021-38199: fs/nfs/nfs4client.c in the Linux kernel before 5.13.4 has incorrect connection-setup ordering, which allows...

fs/nfs/nfs4client.c in the Linux kernel before 5.13.4 has incorrect connection-setup ordering, which allows operators of remote NFSv4 servers to cause a denial of service (hanging of mounts) by arranging for those servers to be unreachable during trunking detection.

UnknownCVSS not scoredNot KEV-listedUpdated
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Glexia's TakeAutomated analysismoderate

Security readout for executives and security teams

Plain-English summary

This issue can make Linux systems hang while mounting NFSv4 storage. A remote NFSv4 server operator can trigger the condition by being unreachable during trunking detection. The direct impact described is denial of service, not data theft or code execution.

Executive priority

Treat this as an availability risk for systems that depend on NFSv4 storage. It is not presented as a compromise path, but stuck mounts can disrupt applications, backup jobs, and operational workflows.

Technical view

Linux kernel fs/nfs/nfs4client.c before 5.13.4 used incorrect connection-setup ordering during NFSv4 trunking detection. If a remote NFSv4 server is unreachable at that point, mounts can hang. The cited upstream commit and 5.13.4 changelog are the primary fix evidence.

Likely exposure

Exposure is likely limited to Linux systems acting as NFSv4 clients, especially where mounts depend on external or less-trusted NFS servers. Systems not using NFSv4 client mounts are unlikely to be affected based on the provided sources.

Exploitation context

No provided source says this is actively exploited, and KEV status is false. The described actor is an operator of a remote NFSv4 server, so risk depends on whether clients mount or attempt to mount such servers.

Researcher notes

The CVE record lacks CVSS, CWE, and structured affected CPE data. The strongest anchors are the Linux 5.13.4 changelog, upstream commit dd99e9f98fbf423ff6d365b37a98e8879170f17c, and downstream Debian advisories.

Mitigation direction

  • Update Linux kernels to 5.13.4 or vendor backported fixed builds.
  • Check Debian and other vendor advisories for package-specific fixed versions.
  • Prioritize systems with business-critical NFSv4 mounts or external NFS dependencies.
  • Monitor vendor guidance if running appliance or distribution kernels.

Validation and detection

  • Inventory Linux systems using NFSv4 client mounts.
  • Confirm kernel builds include the upstream fix or a vendor backport.
  • Review mount logs for unexplained NFSv4 hangs during connection setup.
  • Validate package versions against Debian or relevant vendor advisories.
Prepared
Confidence
medium
Sources
8

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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CVE-2021-38199 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
0Timeline events
0ADP providers
7Source links

CVSS and timeline data

No CVSS vectors or timeline events were available in the normalized CVE source material.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
n/an/an/aListed
Weakness

CWE details

No CWE listed

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