CVE-2021-42143Public exploitNetwork attack vector

Service hang and disclosure via odd cipher length

Published Jan 24, 2024 · Updated Jun 20, 2025

Infinite loop in Contiki-NG tinyDTLS through 2018-08-30 allows remote attackers to hang DTLS servers and read unintended memory. An odd cipher-suite byte count reaches dtls_update_parameters, whose loop subtracts two until the count equals zero, an impossible exit condition for an odd starting value. No authentication or user interaction is required; one crafted ClientHello can exhaust processing resources while the buffer over-read discloses sensitive information.

CVSS severity9.1
Critical
EPSS probability0.81%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Infinite loop in Contiki-NG tinyDTLS through 2018-08-30 allows remote attackers to hang DTLS servers and read unintended memory. An odd cipher-suite byte count reaches dtls_update_parameters, whose loop subtracts two until the count equals zero, an impossible exit condition for an odd starting value. No authentication or user interaction is required; one crafted ClientHello can exhaust processing resources while the buffer over-read discloses sensitive information.

The record

CVE
CVE-2021-42143
Published
Jan 24, 2024
Updated
Jun 20, 2025
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-835, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jan 24, 2024CVE publishedPublication date reported by the CVE source.
  2. Jun 20, 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 exploitPublished

Weakness, pattern, technique

CWE-835Loop with Unreachable Exit Condition ('Infinite Loop')
T1499.004Application or System Exploitation

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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