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CVE Record

CVE-2021-38166: In kernel/bpf/hashtab.c in the Linux kernel through 5.13.8, there is an integer overflow and out-of-bounds...

In kernel/bpf/hashtab.c in the Linux kernel through 5.13.8, there is an integer overflow and out-of-bounds write when many elements are placed in a single bucket. NOTE: exploitation might be impractical without the CAP_SYS_ADMIN capability.

UnknownCVSS not scoredNot KEV-listedUpdated
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Glexia's TakeAutomated analysismoderate

Security readout for executives and security teams

Plain-English summary

CVE-2021-38166 is a Linux kernel eBPF hash table memory corruption bug. It can trigger an integer overflow and out-of-bounds write when many entries land in one bucket. The source notes exploitation may be impractical without CAP_SYS_ADMIN, so business urgency depends on who can use privileged BPF capabilities on affected systems.

Executive priority

Prioritize patching on multi-user Linux hosts, container platforms, and systems granting broad administrative capabilities. The issue is kernel memory corruption, but available evidence suggests constrained exploitability and no confirmed active exploitation in the provided sources.

Technical view

The issue is in kernel/bpf/hashtab.c in Linux through 5.13.8. A crafted high-collision bucket state can overflow internal accounting and write out of bounds. Upstream fixed it in the BPF tree, and Fedora and Debian issued kernel updates. No CVSS, CWE, or KEV exploitation signal is provided.

Likely exposure

Exposure is likely limited to Linux systems running affected kernels through 5.13.8, especially where users, containers, or services can exercise BPF functionality with CAP_SYS_ADMIN. Fedora and Debian published updates, and NetApp published an advisory. Vendor backports may mean package version checks are more reliable than upstream version strings alone.

Exploitation context

The public CVE text says exploitation might be impractical without CAP_SYS_ADMIN. The provided sources do not show active exploitation, public weaponization, or CISA KEV listing. Treat this as a local privileged or highly constrained attack surface unless vendor guidance for a specific platform says otherwise.

Researcher notes

Focus validation on kernel provenance, backported fixes, and CAP_SYS_ADMIN exposure. The affected field in the CVE bundle is generic, so distro advisory mapping is essential. Avoid assuming exploitability or impact beyond the stated integer overflow and out-of-bounds write.

Mitigation direction

  • Apply kernel updates from your Linux distribution or appliance vendor.
  • Verify whether the upstream BPF fix is included in deployed kernels.
  • Review Debian DSA-4978 and Fedora advisories for affected package guidance.
  • Review NetApp advisory if NetApp products are in scope.
  • Limit CAP_SYS_ADMIN and unnecessary BPF access where operationally feasible.

Validation and detection

  • Inventory Linux kernel versions and vendor kernel package revisions.
  • Check whether deployed kernels include the referenced upstream BPF commit.
  • Identify users, services, and containers granted CAP_SYS_ADMIN.
  • Confirm Debian, Fedora, or vendor advisory applicability to each asset.
  • Document exceptions where kernel upgrades are deferred.
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-2021-38166 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.