CVE-2021-3436Public exploit

Bluetooth reconnection disruption via duplicate bond overwrite

Published Oct 5, 2021 · Updated Sep 16, 2024

Duplicate bond handling in Zephyr RTOS 1.14.2, 2.4.0, and 2.5.0 allows physically proximate attackers to disrupt reconnections. During Bluetooth identity-address distribution, the key store fails to reject an existing bond with the same identity, creating duplicate RAM entries while replacing the persistent entry. Exploitation requires the bond identity address and a new pairing with changed keys; later encryption selects stale keys, fails its MIC check, and disconnects.

CVSS severity4.3
Medium
EPSS probability0.98%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Duplicate bond handling in Zephyr RTOS 1.14.2, 2.4.0, and 2.5.0 allows physically proximate attackers to disrupt reconnections. During Bluetooth identity-address distribution, the key store fails to reject an existing bond with the same identity, creating duplicate RAM entries while replacing the persistent entry. Exploitation requires the bond identity address and a new pairing with changed keys; later encryption selects stale keys, fails its MIC check, and disconnects.

The record

CVE
CVE-2021-3436
Published
Oct 5, 2021
Updated
Sep 16, 2024
Vendor
Zephyr Project
Product
Zephyr RTOS
Classifications
CWE-694, T1499
Attack vector
adjacent
Privileges
unauthenticated

Timeline

How it unfolded

  1. Oct 5, 2021CVE publishedPublication date reported by the CVE source.
  2. Sep 16, 2024Record 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=1.14.2 <unspecified
  2. Affected versionversion=2.4.0 <unspecified
  3. Affected versionversion=2.5.0 <unspecified

What conditions does exploitation require?

Attack vectoradjacent
Required privilegesunauthenticated

What is affected?

Zephyr Project · Zephyr RTOSversion=1.14.2 <unspecified; version=2.4.0 <unspecified; version=2.5.0 <unspecified

Published CVSS scores

6.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:L
4.3Zephyr ProjectCVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

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.

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No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectoradjacent
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-694Use of Multiple Resources with Duplicate Identifier
T1499Endpoint Denial of Service

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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