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ZephyrOperating system · Zephyrproject

CVE-2024-1638

CRITICAL · 9.1 CVSS v3.1 Published 2024-02-19
Fix available
A fix is available. Upgrade to after 3.5.0 or later.
See remediation →
100/100
Remediation priority · Urgent
Public exploit Remotely reachable No privileges Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
The documentation specifies that the BT_GATT_PERM_READ_LESC and BT_GATT_PERM_WRITE_LESC defines for a Bluetooth characteristic: Attribute read/write permission with LE Secure Connection encryption. If set, requires that LE Secure Connections is used for read/write access, however this is only true when it is combined with other permissions, namely BT_GATT_PERM_READ_ENCRYPT/BT_GATT_PERM_READ_AUTHEN (for read) or BT_GATT_PERM_WRITE_ENCRYPT/BT_GATT_PERM_WRITE_AUTHEN (for write), if these additional permissions are not set (even in secure connections only mode) then the stack does not perform any permission checks on these characteristics and they can be freely written/read.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis
How this class of weakness works · CWE-20

The application accepts input without confirming it is well-formed or within expected bounds, so malformed data can push the program into states its author never anticipated. Attackers probe these gaps to trigger crashes, bypass logic, or feed tainted values into more dangerous operations downstream. Remediating it well means validating and normalising every input at the boundary against a strict allow-list — not merely filtering known-bad values.

General guidance for the improper input validation class — the official description and references above are authoritative for this specific CVE. Want a bespoke review and a reviewed fix? Ask our team →

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
ZephyrOperating system
Affected:<= 3.5.0

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
None

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to a release after 3.5.0
Recommended fix Moderate confidence

Zephyr 3.6.0 or later

  1. 1. Identify all Zephyr-based products using BT_GATT_PERM_READ_LESC or BT_GATT_PERM_WRITE_LESC permissions
  2. 2. Review the Bluetooth GATT attribute permissions in your code to ensure proper permission combinations
  3. 3. If using LESC permissions without BT_GATT_PERM_READ_ENCRYPT/BT_GATT_PERM_READ_AUTHEN (for read) or BT_GATT_PERM_WRITE_ENCRYPT/BT_GATT_PERM_WRITE_AUTHEN (for write), add the required additional permissions
  4. 4. Upgrade Zephyr to version 3.6.0 or later which contains the fix for this vulnerability
  5. 5. Rebuild and test the application, specifically verifying Bluetooth characteristic read/write permissions work correctly with LE Secure Connections
  6. 6. Verify that characteristics with LESC permissions cannot be accessed without proper LE Secure Connections encryption after the upgrade
Caveat Ensure your Bluetooth characteristic permission configurations are correct - review any custom GATT services using LESC permissions

Generated from the published advisory — verify against the referenced sources before acting.

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2024-1638 in production — separate from our analysis above.

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