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CVE Record

CVE-2021-46952: NFS: fs_context: validate UDP retrans to prevent shift out-of-bounds

In the Linux kernel, the following vulnerability has been resolved: NFS: fs_context: validate UDP retrans to prevent shift out-of-bounds Fix shift out-of-bounds in xprt_calc_majortimeo(). This is caused by a garbage timeout (retrans) mount option being passed to nfs mount, in this case from syzkaller. If the protocol is XPRT_TRANSPORT_UDP, then 'retrans' is a shift value for a 64-bit long integer, so 'retrans' cannot be >= 64. If it is >= 64, fail the mount and return an error.

UnknownCVSS not scoredNot KEV-listedUpdated
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Glexia's TakeAutomated analysisunknown

Security readout for executives and security teams

Plain-English summary

CVE-2021-46952 is a Linux kernel NFS bug where an invalid UDP NFS mount timeout setting could trigger an out-of-bounds bit shift. The published fix validates the value and rejects the mount. The source bundle does not provide CVSS, CWE, business impact, or evidence of active exploitation.

Executive priority

Treat as a routine kernel remediation item unless your environment relies heavily on UDP NFS mounts or delegates mount configuration. There is no provided evidence of active exploitation, but kernel undefined behavior should still be removed through normal patch cycles.

Technical view

The issue is in NFS fs_context handling. For XPRT_TRANSPORT_UDP, the retrans mount option is used as a shift value for a 64-bit long integer in xprt_calc_majortimeo(). Values 64 or higher must be rejected to avoid shift out-of-bounds behavior.

Likely exposure

Exposure is most relevant to Linux systems that perform NFS mounts over UDP and accept configurable mount options. The bundle does not show remote unauthenticated exposure, privilege requirements, or affected distribution packages, so asset owners should map kernel versions and vendor backports.

Exploitation context

The source says the bad value came from syzkaller fuzzing. KEV is false, and no provided source reports active exploitation, public weaponization, or exploitation in the wild.

Researcher notes

The bundle lacks CVSS, CWE, and explicit impact beyond shift out-of-bounds. Avoid inferring code execution or remote exploitability. The core fix is a bounds check: for UDP transport, retrans must be below 64 or the mount fails with an error.

Mitigation direction

  • Apply a Linux kernel update containing the referenced stable fixes.
  • Check distribution vendor advisories for backported package versions.
  • Restrict who can initiate or modify NFS mount options.
  • Prefer vendor-supported NFS configurations and avoid unsupported UDP mount settings.
  • Track this as kernel maintenance unless vendor guidance raises severity.

Validation and detection

  • Inventory Linux kernel versions on systems using NFS.
  • Identify hosts using NFS mounts over UDP.
  • Confirm the running kernel includes the retrans validation fix.
  • Verify invalid UDP retrans values are rejected safely.
  • Review vendor advisories for affected and fixed package mappings.
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

These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.

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CVE-2021-46952 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

CISA-ADPCISA ADP Vulnrichment
other:ssvc
CVECVE Program Container

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
LinuxLinux9954bf92c0cddd50a2a470be302e1c1ffdf21d42, 9954bf92c0cddd50a2a470be302e1c1ffdf21d42, 9954bf92c0cddd50a2a470be302e1c1ffdf21d42, 9954bf92c0cddd50a2a470be302e1c1ffdf21d42unaffected
LinuxLinux5.6, 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.