CVE-2021-21281: Buffer overflow due to unvalidated TCP data offset

Severity: critical (CVSS 9.8 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.9% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2021-06-18 · updated 2026-06-17
Weakness: CWE-120

Description

Contiki-NG is an open-source, cross-platform operating system for internet of things devices. A buffer overflow vulnerability exists in Contiki-NG versions prior to 4.6. After establishing a TCP socket using the tcp-socket library, it is possible for the remote end to send a packet with a data offset that is unvalidated. The problem has been patched in Contiki-NG 4.6. Users can apply the patch for this vulnerability out-of-band as a workaround.

Affected products

contiki-ng: before 4.6 — fixed in 4.6

How to fix

Upgrade to a fixed version: contiki-ng 4.6. Check the vendor advisory for mitigations.

References

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