Security readout for executives and security teams
Plain-English summary
CVE-2021-21281 is a high-severity memory safety flaw in Contiki-NG before 4.6. A remote TCP peer can send malformed TCP metadata after a socket is established, potentially causing device crashes and limited confidentiality or integrity impact. The vendor patched it in Contiki-NG 4.6.
Executive priority
Treat as high priority for connected IoT products using affected Contiki-NG TCP functionality, especially exposed devices. For organizations without Contiki-NG deployments, priority is inventory confirmation rather than emergency response.
Technical view
The vulnerability is a CWE-120 buffer overflow in Contiki-NG's tcp-socket library. The TCP data offset from a remote packet was not validated after socket establishment. CVSS 3.1 is 7.0 with network attack vector, no privileges, no user interaction, high attack complexity, and high availability impact.
Likely exposure
Exposure is likely limited to IoT firmware or products using Contiki-NG versions earlier than 4.6 and the tcp-socket library. Risk increases when those TCP services are reachable from untrusted networks or peers.
Exploitation context
The provided sources do not show active exploitation, and the CVE is not marked KEV. Exploitation is described as remote but high complexity, requiring an established TCP socket and a malformed packet with an unvalidated data offset.
Researcher notes
The strongest evidence is the vendor advisory and pull request. The sources identify affected versions and patch availability, but do not provide proof of exploitation, affected downstream products, or compensating controls beyond upgrading or applying the patch.
Mitigation direction
- Upgrade Contiki-NG to version 4.6 or later.
- Apply the vendor patch out-of-band if full upgrade is not immediately possible.
- Limit exposure of Contiki-NG TCP services to trusted networks and peers.
- Review affected firmware release plans for devices still shipping Contiki-NG before 4.6.
Validation and detection
- Inventory products, firmware, and SBOMs for Contiki-NG versions earlier than 4.6.
- Confirm whether the tcp-socket library is compiled in and reachable over TCP.
- Verify the Contiki-NG 4.6 fix or related patch is present in source or firmware.
- Check device crash telemetry for suspicious TCP-adjacent failures, without assuming exploitation.
Public sources used
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
Conservative CVE-to-ATT&CK context
These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.
ATT&CK lookup starting points
Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.
CWE-120: Exact CWE lookup
Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.
Open ATT&CK lookupCVE-2021-21281 mapping review
Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.
Open ATT&CK lookup- Severity
- High
- CVSS
- 7 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H
CNA and ADP enrichment extracted from CVE v5
These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.
CVSS vector scores
1 official scoreWe collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H2.24.7Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
7HighVector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H
Source materials
- CVE List V5 sourceCVE List V5
- https://github.com/contiki-ng/contiki-ng/security/advisories/GHSA-mc42-fqfr-h9fpCVE reference · x_refsource_CONFIRM
- https://github.com/contiki-ng/contiki-ng/pull/1366CVE reference · x_refsource_MISC
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.
Buffer Copy without Checking Size of Input ('Classic Buffer Overflow')
Buffer Copy without Checking Size of Input ('Classic Buffer Overflow') represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.