CVE-2021-42142Network attack vector

Denial of service via descending handshake epochs

Published Jan 23, 2024 · Updated Jun 11, 2025

Improper epoch handling in Contiki-NG tinyDTLS revision 53a0d97 allows remote attackers to interrupt DTLS traffic through crafted handshakes. The DTLS server completes two handshakes when the first uses a larger epoch number than the second, instead of rejecting the descending epoch sequence. Unauthenticated network access to the DTLS service is sufficient to induce false-positive packet drops; no process crash or reboot is reported.

CVSS severity9.8
Critical
EPSS probability0.99%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper epoch handling in Contiki-NG tinyDTLS revision 53a0d97 allows remote attackers to interrupt DTLS traffic through crafted handshakes. The DTLS server completes two handshakes when the first uses a larger epoch number than the second, instead of rejecting the descending epoch sequence. Unauthenticated network access to the DTLS service is sufficient to induce false-positive packet drops; no process crash or reboot is reported.

The record

CVE
CVE-2021-42142
Published
Jan 23, 2024
Updated
Jun 11, 2025
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-755, CWE-770, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jan 23, 2024CVE publishedPublication date reported by the CVE source.
  2. Jun 11, 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

9.8NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
8.2CISA-ADPCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/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-755Improper Handling of Exceptional Conditions
CWE-770Allocation of Resources Without Limits or Throttling
T1499.004Application or System Exploitation Flood

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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