CVE-2021-35953Network attack vector

Device outage via crafted characteristic value bytes

Published Dec 26, 2022 · Updated Apr 14, 2025

Denial of service in Fastrack Reflex 2.0 firmware 90.89 allows remote attackers to cause an outage via a crafted characteristic value. Writing selected values in the final three bytes of the watch's Bluetooth characteristic crashes the tracker; it restarts after five minutes, but Bluetooth remains unavailable. No authentication or user interaction is required, but the attacker must be within Bluetooth range, and the demonstrated consequence is loss of device and network availability.

CVSS severity7.5
High
EPSS probability0.84%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Denial of service in Fastrack Reflex 2.0 firmware 90.89 allows remote attackers to cause an outage via a crafted characteristic value. Writing selected values in the final three bytes of the watch's Bluetooth characteristic crashes the tracker; it restarts after five minutes, but Bluetooth remains unavailable. No authentication or user interaction is required, but the attacker must be within Bluetooth range, and the demonstrated consequence is loss of device and network availability.

The record

CVE
CVE-2021-35953
Published
Dec 26, 2022
Updated
Apr 14, 2025
Vendor
Unknown vendor
Product
Unknown product
Classifications
T1499
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Dec 26, 2022CVE publishedPublication date reported by the CVE source.
  2. Apr 14, 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?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

7.5CISA-ADPCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
7.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

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)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

T1499Endpoint Denial of Service

Public exploit references

No public exploit references are available in this record.

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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