Security readout for executives and security teams
Plain-English summary
CVE-2021-3329 affects Zephyr’s Bluetooth host stack. Improper validation during HCI host initialization can crash the Bluetooth stack when handling the initial ACL_MTU handshake packet. For products using Zephyr with Bluetooth enabled, this is primarily an availability risk within Bluetooth range.
Executive priority
Treat this as high priority for Bluetooth-enabled Zephyr products, especially operational or customer-facing devices. The severity is critical, but urgency depends on confirmed Zephyr use, Bluetooth exposure, and whether vendor guidance identifies the deployed version as affected.
Technical view
The issue is classified under CWE-703: improper handling of exceptional conditions. The CVSS 3.1 vector is adjacent-network, low complexity, no privileges, no user interaction, scope changed, with confidentiality low, integrity high, and availability high impact. Public source detail does not identify affected Zephyr versions.
Likely exposure
Exposure is most likely in embedded or IoT products built on Zephyr that enable the Bluetooth host stack. The affected versions are listed only as unspecified, so teams need SBOM, firmware, and vendor advisory review to confirm exposure.
Exploitation context
The CVSS vector indicates exploitation from an adjacent network, consistent with Bluetooth-range access. The source bundle does not show CISA KEV listing or cited evidence of active exploitation. Public details support a crash condition, but do not provide complete exploit status or version scope.
Researcher notes
Evidence is sparse: the public description names a Bluetooth HCI initialization validation failure and crash, but affected versions are unspecified. The CVSS vector suggests adjacent, unauthenticated attack conditions. Do not assume active exploitation or a specific patch without confirming Zephyr advisory details.
Mitigation direction
- Check Zephyr ZEPSEC-117 and vendor guidance for affected branches and fixes.
- Update affected Zephyr-based firmware to a vendor-supported fixed release when identified.
- Disable Bluetooth on products where it is not required.
- Prioritize devices where Bluetooth disruption affects safety, operations, or customer availability.
- Track downstream OEM advisories for products embedding Zephyr.
Validation and detection
- Inventory products and firmware builds that include Zephyr.
- Confirm whether the Bluetooth host stack is enabled in each build.
- Map deployed Zephyr versions against ZEPSEC-117 and vendor advisories.
- Review device logs for unexplained Bluetooth stack crashes or resets.
- Validate fixes in a lab before production firmware rollout.
Public sources used
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
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
Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.
CWE-703: Exact CWE lookup
Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.
Open ATT&CK lookupCVE-2021-3329 mapping review
Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.
Open ATT&CK lookup- Severity
- Critical
- CVSS
- 9.6 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/C:L/I:H/A:H
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.
CVSS vector scores
1 official scoreWe collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.
CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/C:L/I:H/A:H2.86Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
9.6CriticalVector: CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/C:L/I:H/A:H
Source materials
- CVE List V5 sourceCVE List V5
- https://zephyrprojectsec.atlassian.net/browse/ZEPSEC-117CVE reference
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.
Improper Check or Handling of Exceptional Conditions
Improper Check or Handling of Exceptional Conditions represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.