CVE-2021-21279Public exploitNetwork attack vector

Remote system hang via ND6 offset wraparound

Published Jun 18, 2021 · Updated Aug 3, 2024

Infinite loop in Contiki-NG before 4.6 allows remote attackers to hang the operating system via crafted IPv6 neighbor solicitations. The ns_input function in os/net/ipv6/uip-nd6.c adds an insufficiently validated option length to the 8-bit nd6_opt_offset counter, allowing crafted packet data to wrap the counter without advancing the options loop. No authentication or user interaction is required; cooperative scheduling leaves the main system and communications stack unable to make progress.

CVSS severity7.5
High
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

Infinite loop in Contiki-NG before 4.6 allows remote attackers to hang the operating system via crafted IPv6 neighbor solicitations. The ns_input function in os/net/ipv6/uip-nd6.c adds an insufficiently validated option length to the 8-bit nd6_opt_offset counter, allowing crafted packet data to wrap the counter without advancing the options loop. No authentication or user interaction is required; cooperative scheduling leaves the main system and communications stack unable to make progress.

The record

CVE
CVE-2021-21279
Published
Jun 18, 2021
Updated
Aug 3, 2024
Vendor
Contiki-NG
Product
Contiki-NG
Classifications
CWE-835, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jun 18, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 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=< 4.6

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Contiki-NG · Contiki-NGversion=< 4.6

Published CVSS scores

7.8NIST NVDAV:N/AC:L/Au:N/C:N/I:N/A:C
7.5GitHub, Inc.CVSS: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.

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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