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CVE Record

CVE-2021-47376: bpf: Add oversize check before call kvcalloc()

In the Linux kernel, the following vulnerability has been resolved: bpf: Add oversize check before call kvcalloc() Commit 7661809d493b ("mm: don't allow oversized kvmalloc() calls") add the oversize check. When the allocation is larger than what kmalloc() supports, the following warning triggered: WARNING: CPU: 0 PID: 8408 at mm/util.c:597 kvmalloc_node+0x108/0x110 mm/util.c:597 Modules linked in: CPU: 0 PID: 8408 Comm: syz-executor221 Not tainted 5.14.0-syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 RIP: 0010:kvmalloc_node+0x108/0x110 mm/util.c:597 Call Trace: kvmalloc include/linux/mm.h:806 [inline] kvmalloc_array include/linux/mm.h:824 [inline] kvcalloc include/linux/mm.h:829 [inline] check_btf_line kernel/bpf/verifier.c:9925 [inline] check_btf_info kernel/bpf/verifier.c:10049 [inline] bpf_check+0xd634/0x150d0 kernel/bpf/verifier.c:13759 bpf_prog_load kernel/bpf/syscall.c:2301 [inline] __sys_bpf+0x11181/0x126e0 kernel/bpf/syscall.c:4587 __do_sys_bpf kernel/bpf/syscall.c:4691 [inline] __se_sys_bpf kernel/bpf/syscall.c:4689 [inline] __x64_sys_bpf+0x78/0x90 kernel/bpf/syscall.c:4689 do_syscall_x64 arch/x86/entry/common.c:50 [inline] do_syscall_64+0x3d/0xb0 arch/x86/entry/common.c:80 entry_SYSCALL_64_after_hwframe+0x44/0xae

UnknownCVSS not scoredNot KEV-listedUpdated
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Glexia's TakeAutomated analysisunknown

Security readout for executives and security teams

Plain-English summary

This Linux kernel issue is a BPF verifier allocation-size bug. A crafted BPF program load with oversized BTF line information could trigger a kernel warning path during memory allocation. The sources do not provide CVSS, confirmed impact beyond the warning, or evidence of active exploitation.

Executive priority

Schedule remediation through normal kernel patching unless local multi-user or container-host exposure makes BPF access plausible. There is no source-backed active exploitation signal, but kernel bugs can have broad operational impact if left unpatched across shared infrastructure.

Technical view

The flaw is in Linux kernel BPF verifier handling around check_btf_line/check_btf_info. Before kvcalloc(), the code lacked an oversize check, allowing an allocation request larger than kvmalloc supports and triggering a warning in kvmalloc_node during bpf_prog_load via the bpf syscall.

Likely exposure

Exposure is limited to Linux kernels in the affected source ranges where callers can reach BPF program loading with BTF metadata. Exact distribution exposure depends on vendor backports and kernel configuration. The bundle identifies Linux as affected but does not list specific distributions or products beyond Linux kernel versions.

Exploitation context

CISA KEV status is false in the bundle, and no cited source reports exploitation in the wild. The evidence comes from a syzkaller-style kernel warning trace, not a public exploit report. Treat this as a kernel reliability and hardening issue unless vendor advisories state a stronger impact.

Researcher notes

Key uncertainty is impact. The record documents an oversize allocation check added before kvcalloc() in BPF verifier BTF processing, but does not establish privilege escalation, denial of service severity, or reachable attacker model. Avoid overstating exploitability without vendor or upstream analysis.

Mitigation direction

  • Identify Linux kernel versions running on affected systems.
  • Check distribution vendor advisories for backported fixes.
  • Update to a kernel containing the referenced stable fixes.
  • Restrict BPF program loading where operationally appropriate.
  • Prioritize internet-facing hosts only if they expose local code execution paths.

Validation and detection

  • Inventory kernel versions and distribution patch levels.
  • Confirm whether referenced stable commits are present or backported.
  • Review BPF availability and policy on multi-user systems.
  • Check kernel logs for related kvmalloc_node or BPF verifier warnings.
  • Track vendor advisories for CVSS, impact, and fixed package names.
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

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ATT&CK lookup starting points

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CVE-2021-47376 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
LinuxLinuxc454a46b5efd8eff8880e88ece2976e60a26bf35, c454a46b5efd8eff8880e88ece2976e60a26bf35, c454a46b5efd8eff8880e88ece2976e60a26bf35, c454a46b5efd8eff8880e88ece2976e60a26bf35unaffected
LinuxLinux5.0, 0, 5.4.150, 5.10.70, 5.14.9, 5.15affected
Weakness

CWE details

No CWE listed

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