CVE-2024-1638Public exploitNetwork attack vector

Unauthorized GATT access via skipped LESC checks

Published Feb 19, 2024 · Updated Apr 24, 2025

Improper input validation in Zephyr Project Zephyr RTOS 3.5.0 and earlier allows remote attackers to read or write protected GATT data via Bluetooth. In bt_gatt_check_perm, the outer condition tests only encryption and authentication masks, so a LESC-only attribute skips the nested secure-connection check. The bypass affects applications that set BT_GATT_PERM_READ_LESC or BT_GATT_PERM_WRITE_LESC without a matching encryption or authentication permission, allowing an unpaired Bluetooth peer to invoke the configured read or write handler.

CVSS severity8.2
High
EPSS probability0.35%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper input validation in Zephyr Project Zephyr RTOS 3.5.0 and earlier allows remote attackers to read or write protected GATT data via Bluetooth. In bt_gatt_check_perm, the outer condition tests only encryption and authentication masks, so a LESC-only attribute skips the nested secure-connection check. The bypass affects applications that set BT_GATT_PERM_READ_LESC or BT_GATT_PERM_WRITE_LESC without a matching encryption or authentication permission, allowing an unpaired Bluetooth peer to invoke the configured read or write handler.

The record

CVE
CVE-2024-1638
Published
Feb 19, 2024
Updated
Apr 24, 2025
Vendor
Zephyr Project
Product
Zephyr RTOS
Classifications
CWE-20, T1210
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Feb 19, 2024CVE publishedPublication date reported by the CVE source.
  2. Apr 24, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=0 <=3.5
  2. Affected versionversion=* <=3.5

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Zephyr Project · Zephyr RTOSversion=0 <=3.5; version=* <=3.5

Published CVSS scores

8.2Zephyr ProjectCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:N
9.1NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-20Improper Input Validation
T1210Exploitation of Remote Services

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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