CVE-2021-42147Network attack vector

Remote server crash via oversized fragment length

Published Jan 24, 2024 · Updated May 30, 2025

Buffer over-read in Contiki-NG tinyDTLS at commit 53a0d97 and earlier allows remote attackers to crash DTLS servers via malformed packets. The server trusts an oversized DTLS fragment Length field and passes a byte count larger than the received buffer to dtls_sha256_update, which reads beyond the packet boundary. No authentication or user interaction is required, and the demonstrated consequence is a segmentation-fault crash of the DTLS service.

CVSS severity9.1
Critical
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

Buffer over-read in Contiki-NG tinyDTLS at commit 53a0d97 and earlier allows remote attackers to crash DTLS servers via malformed packets. The server trusts an oversized DTLS fragment Length field and passes a byte count larger than the received buffer to dtls_sha256_update, which reads beyond the packet boundary. No authentication or user interaction is required, and the demonstrated consequence is a segmentation-fault crash of the DTLS service.

The record

CVE
CVE-2021-42147
Published
Jan 24, 2024
Updated
May 30, 2025
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-125, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jan 24, 2024CVE publishedPublication date reported by the CVE source.
  2. May 30, 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

9.1CISA-ADPCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H
9.1NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/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.

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 exploitUnconfirmed

Weakness, pattern, technique

CWE-125Out-of-bounds Read
T1499.004Endpoint Denial of Service: Application or System Exploitation

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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