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CVE Record

CVE-2021-33034: In the Linux kernel before 5.12.4, net/bluetooth/hci_event.c has a use-after-free when destroying an hci_ch...

In the Linux kernel before 5.12.4, net/bluetooth/hci_event.c has a use-after-free when destroying an hci_chan, aka CID-5c4c8c954409. This leads to writing an arbitrary value.

UnknownCVSS not scoredNot KEV-listedUpdated
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Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

This is a Linux kernel Bluetooth memory-safety flaw fixed before kernel 5.12.4. The CVE says it can result in writing an arbitrary value, which is potentially serious, but the provided sources do not include a CVSS score or confirmed exploitation.

Executive priority

Treat this as a high-priority kernel patching item, especially for Linux endpoints or servers with Bluetooth capability. No active exploitation is cited, but kernel memory corruption with arbitrary write impact has meaningful security risk.

Technical view

CVE-2021-33034 is a use-after-free in net/bluetooth/hci_event.c when destroying an hci_chan. The issue is associated with upstream commit 5c4c8c954409 and appears in the Linux 5.12.4 changelog. Public syzkaller and SyzScope records discuss the underlying crash condition.

Likely exposure

Exposure is most likely on systems running affected Linux kernels before the fixed upstream state, particularly where the Bluetooth stack is present. Downstream impact depends on distribution backports, so package version alone may not map directly to kernel.org versions.

Exploitation context

The source bundle does not show CISA KEV listing, active exploitation, or a public weaponized exploit. Evidence is limited to the CVE description, fuzzing-related reports, upstream fix reference, changelog entry, and Fedora/Debian security update references.

Researcher notes

The bundle lacks CVSS, CWE, affected CPEs, and exploit prerequisites. Validate against upstream commit 5c4c8c954409, kernel 5.12.4 changelog, and distro advisories rather than assuming all pre-5.12.4 packages are unpatched.

Mitigation direction

  • Apply vendor Linux kernel security updates for affected systems.
  • Confirm the kernel includes upstream commit 5c4c8c954409 or an equivalent backport.
  • Prioritize systems with Bluetooth enabled or exposed to untrusted local users.
  • If patching is delayed, check vendor guidance for supported compensating controls.

Validation and detection

  • Inventory Linux kernel versions and distribution security advisory status.
  • Check whether the running kernel includes the fixed Bluetooth change or distro backport.
  • Identify systems with Bluetooth hardware, modules, or services enabled.
  • Review vulnerability scanner findings against vendor advisory package versions.
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

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.

ATT&CK lookup starting points

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CVE-2021-33034 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.