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CVE-2021-33200: kernel/bpf/verifier.c in the Linux kernel through 5.12.7 enforces incorrect limits for pointer arithmetic o...

kernel/bpf/verifier.c in the Linux kernel through 5.12.7 enforces incorrect limits for pointer arithmetic operations, aka CID-bb01a1bba579. This can be abused to perform out-of-bounds reads and writes in kernel memory, leading to local privilege escalation to root. In particular, there is a corner case where the off reg causes a masking direction change, which then results in an incorrect final aux->alu_limit.

UnknownCVSS not scoredNot KEV-listedUpdated
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Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

CVE-2021-33200 is a Linux kernel eBPF verifier flaw that can let a local attacker gain root privileges. The available sources describe kernel memory out-of-bounds reads and writes caused by incorrect pointer arithmetic limits. This is most urgent on multi-user systems, shared servers, and container hosts where untrusted users can run local code.

Executive priority

High priority where users, workloads, or containers are not fully trusted. The flaw requires local execution, but successful exploitation can convert limited access into root control, increasing breach impact and lateral movement risk. Patch through normal emergency kernel-update processes for exposed shared infrastructure.

Technical view

The issue is in kernel/bpf/verifier.c in Linux kernels through 5.12.7. A corner case in verifier arithmetic changes masking direction and produces an incorrect aux->alu_limit, allowing out-of-bounds kernel memory access. The CVE record links upstream Linux commits and Fedora advisories, but the bundle does not provide CVSS scoring or full downstream product scope.

Likely exposure

Exposure likely applies to Linux systems running affected kernels through 5.12.7 or vendor backports missing the referenced fixes. Fedora advisories and a NetApp advisory are cited, but this bundle does not identify exact package versions, appliances, or configurations beyond the Linux kernel description.

Exploitation context

The source bundle supports local privilege escalation to root. It does not show CISA KEV listing, confirmed active exploitation, remote exploitation, or public weaponization details. Treat this as a serious post-access escalation risk, not as an internet-facing remote entry point based on the provided evidence.

Researcher notes

Focus validation on kernel provenance and backport status. The key technical signal is incorrect eBPF verifier pointer arithmetic limit enforcement in kernel/bpf/verifier.c. The bundle cites upstream commits but lacks CVSS, CWE, exploit maturity, and exact downstream package boundaries, so avoid overclaiming impact beyond local root escalation.

Mitigation direction

  • Apply vendor kernel security updates that include the referenced upstream fixes.
  • Check Fedora and NetApp guidance if those environments are present.
  • Prioritize shared systems, container hosts, and servers with untrusted local users.
  • Reduce untrusted local code execution until patched.
  • Track vendor backport status rather than relying only on kernel version strings.

Validation and detection

  • Inventory Linux kernel versions and vendor package build levels.
  • Confirm whether kernels are through 5.12.7 or missing backported fixes.
  • Review vendor advisories for exact fixed package versions.
  • Verify patched hosts after reboot into the updated kernel.
  • Document exceptions where vendor impact is unclear or unsupported.
Prepared
Confidence
medium
Sources
9

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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Privilege behavior lookup

The CVE wording references privilege impact, so privilege escalation and authorization behavior review may help. This is a Glexia inferred lookup path, not an official MITRE, ATT&CK, or CVE Program mapping.

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CVE-2021-33200 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
8Source 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.