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CVE Record

CVE-2021-46908: bpf: Use correct permission flag for mixed signed bounds arithmetic

In the Linux kernel, the following vulnerability has been resolved: bpf: Use correct permission flag for mixed signed bounds arithmetic We forbid adding unknown scalars with mixed signed bounds due to the spectre v1 masking mitigation. Hence this also needs bypass_spec_v1 flag instead of allow_ptr_leaks.

UnknownCVSS not scoredNot KEV-listedUpdated
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Glexia's TakeAutomated analysisunknown

Security readout for executives and security teams

Plain-English summary

This is a Linux kernel BPF verification bug tied to Spectre v1 defenses. The kernel used the wrong permission flag for a restricted arithmetic case, affecting how unsafe BPF operations are blocked. The source bundle provides no CVSS score or confirmed exploit activity.

Executive priority

Treat this as a kernel hygiene issue until vendor severity is clearer. It should be handled through normal kernel patching, with higher priority for shared, multi-tenant, or container-hosting systems where BPF access could matter.

Technical view

The Linux BPF verifier used allow_ptr_leaks where bypass_spec_v1 was required for unknown scalar arithmetic with mixed signed bounds. The kernel note says this arithmetic is forbidden because of Spectre v1 masking mitigation, so the fix aligns the permission check with that mitigation path.

Likely exposure

Exposure is limited to systems running the listed affected Linux kernel versions or vulnerable commits. The bundle names Linux 5.8, 5.10.32, 5.11.16, and 5.12, but does not identify distributions, appliances, or configuration-dependent reachability.

Exploitation context

The bundle does not report active exploitation, public exploit code, or CISA KEV inclusion. Practical risk depends on whether an attacker can reach BPF program loading paths and whether kernel hardening or vendor backports are present.

Researcher notes

The available description is narrow and upstream-focused. It identifies a permission flag mismatch in BPF verifier logic for Spectre v1 masking mitigation, but gives no CVSS, CWE, proof-of-concept, exploitability analysis, or distribution-specific affected package list.

Mitigation direction

  • Check your distribution kernel advisory for CVE-2021-46908 coverage.
  • Upgrade to a kernel containing the referenced stable fixes.
  • Prioritize hosts that permit broader BPF program loading.
  • Review BPF access restrictions on multi-user or container hosts.
  • Track vendor backports rather than relying only on upstream version numbers.

Validation and detection

  • Inventory Linux kernel versions across servers and images.
  • Map installed vendor kernels to their CVE-2021-46908 advisory status.
  • Confirm whether the referenced stable commits are backported.
  • Review which users or services can load BPF programs.
  • Document any exposed systems awaiting vendor fixes.
Prepared
Confidence
medium
Sources
5

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-2021-46908 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
4Source 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
LinuxLinux2c78ee898d8f10ae6fb2fa23a3fbaec96b1b7366, 2c78ee898d8f10ae6fb2fa23a3fbaec96b1b7366, 2c78ee898d8f10ae6fb2fa23a3fbaec96b1b7366unaffected
LinuxLinux5.8, 0, 5.10.32, 5.11.16, 5.12affected
Weakness

CWE details

No CWE listed

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