CVE-2021-42147 is a critical buffer over-read vulnerability identified in the dtls_sha256_update function within the tinyDTLS implementation used by Contiki-NG, an open-source operating system for Internet of Things (IoT) devices. The vulnerability arises due to improper bounds checking in the dtls_sha256_update function, which processes incoming DTLS (Datagram Transport Layer Security) packets. Specifically, crafted data packets can trigger a buffer over-read condition, where the function reads beyond the allocated memory buffer. This flaw can be exploited remotely by an unauthenticated attacker sending maliciously crafted DTLS packets to vulnerable devices. The consequence of this vulnerability is a denial of service (DoS) condition, where the affected device may crash or become unresponsive, disrupting normal operations. The CVSS v3.1 base score of 9.1 reflects the critical severity, with an attack vector of network (AV:N), no privileges required (PR:N), no user interaction (UI:N), and high impact on confidentiality and availability (C:H/A:H) but no impact on integrity (I:N). The vulnerability is classified under CWE-125 (Out-of-bounds Read), indicating a memory safety issue. No known public exploits have been reported in the wild, and no official patches or vendor advisories are listed, which may suggest limited awareness or deployment of fixes. Given that tinyDTLS is commonly used in constrained IoT environments, this vulnerability poses a significant risk to embedded systems relying on Contiki-NG for secure communication, especially in scenarios where DTLS is used to protect data confidentiality and device authentication over UDP transport.

For European organizations, the impact of CVE-2021-42147 can be substantial, particularly for industries and sectors that deploy IoT devices running Contiki-NG or tinyDTLS for secure communications. These include smart city infrastructure, industrial control systems, healthcare devices, and critical infrastructure monitoring. A successful exploitation could lead to denial of service on IoT endpoints, causing operational disruptions, loss of telemetry data, and potential cascading failures in automated systems. The high confidentiality impact indicates that sensitive information processed by the DTLS session could be exposed or inferred, raising privacy and compliance concerns under regulations such as GDPR. Availability impacts could affect service continuity, especially in environments where IoT devices perform real-time monitoring or control functions. Although no known exploits are currently active in the wild, the critical severity and network attack vector imply that attackers could develop exploits with relative ease, increasing the urgency for European organizations to assess their exposure. The lack of patches or vendor guidance complicates mitigation efforts, potentially prolonging the window of vulnerability.

European organizations should take a proactive approach to mitigate this vulnerability. First, conduct an inventory of IoT devices and embedded systems using Contiki-NG and tinyDTLS to identify potentially affected assets. Engage with device manufacturers or open-source project maintainers to obtain patches or updated versions that address the vulnerability; if none are available, consider applying custom code reviews or patches to the dtls_sha256_update function to enforce strict bounds checking. Network-level mitigations include deploying intrusion detection/prevention systems (IDS/IPS) with signatures or anomaly detection rules targeting malformed DTLS packets to block or alert on suspicious traffic. Segment IoT networks to limit exposure and restrict access to critical devices from untrusted networks. Implement rate limiting and filtering on UDP ports used by DTLS to reduce the risk of exploitation attempts. Regularly monitor device logs and network traffic for signs of exploitation attempts or abnormal behavior. Finally, develop incident response plans specific to IoT device failures to minimize operational impact in case of successful attacks.