CVE-2021-21281Network attack vector

Device crash via unchecked TCP data offset

Published Jun 18, 2021 · Updated Aug 3, 2024

Buffer overflow in Contiki-NG before 4.6 allows remote attackers to crash a device via a malformed packet sent over an established TCP socket. The IPv6 TCP input path stores the packet's TCP data offset in c without checking it against the received length, then subtracts it from uip_len before tcp-socket.c copies an oversized length. Exploitation requires an established TCP socket; the resulting copy reads beyond uip_buf and crashes the device.

CVSS severity7.0
High
EPSS probability0.92%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Buffer overflow in Contiki-NG before 4.6 allows remote attackers to crash a device via a malformed packet sent over an established TCP socket. The IPv6 TCP input path stores the packet's TCP data offset in c without checking it against the received length, then subtracts it from uip_len before tcp-socket.c copies an oversized length. Exploitation requires an established TCP socket; the resulting copy reads beyond uip_buf and crashes the device.

The record

CVE
CVE-2021-21281
Published
Jun 18, 2021
Updated
Aug 3, 2024
Vendor
Contiki-NG
Product
Contiki-NG
Classifications
CWE-120, 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

7.5NIST NVDAV:N/AC:L/Au:N/C:P/I:P/A:P
7.0GitHub, Inc.CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H
9.8NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/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-120Buffer Copy without Checking Size of Input ('Classic Buffer Overflow')
T1499.004Endpoint Denial of Service: Application or System Exploitation

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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