CVE-2021-38386 in Contiki
Summary
by MITRE • 08/11/2021
In Contiki 3.0, a buffer overflow in the Telnet service allows remote attackers to cause a denial of service because the ls command is mishandled when a directory has many files with long names.
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Analysis
by VulDB Data Team • 08/15/2021
The vulnerability identified as CVE-2021-38386 resides within the Contiki 3.0 operating system's Telnet service implementation, representing a critical buffer overflow flaw that can be exploited remotely to execute denial of service attacks. This issue specifically manifests when the ls command processes directories containing numerous files with exceptionally long filenames, creating a scenario where memory boundaries are exceeded during command execution. The vulnerability demonstrates characteristics consistent with CWE-121, which describes stack-based buffer overflow conditions, and aligns with ATT&CK technique T1499.004 for network denial of service attacks. Contiki, a lightweight operating system designed for embedded devices and the internet of things, is particularly susceptible to such flaws due to its constrained memory environment and the limited security considerations inherent in resource-constrained systems. The Telnet service, while providing essential remote access capabilities for device management, becomes a vector for exploitation when handling directory listings with excessive file name lengths.
The technical mechanism behind this vulnerability involves improper input validation and memory management within the ls command implementation of Contiki's Telnet service. When processing directories containing many files with long names, the system fails to adequately check buffer boundaries before copying or formatting directory entry information into allocated memory segments. This oversight allows attackers to craft malicious directory structures or file names that exceed the allocated buffer space, causing memory corruption that results in service termination or system instability. The flaw is particularly dangerous in embedded environments where automatic restart mechanisms may not be present, potentially leading to complete system unavailability. The vulnerability can be exploited remotely without authentication requirements, making it especially concerning for networked devices that rely on Telnet for administrative access. Attackers can trigger the overflow by connecting to the Telnet service and executing the ls command against specifically crafted directories, thereby leveraging the system's failure to properly handle extended input lengths.
The operational impact of CVE-2021-38386 extends beyond simple service disruption to potentially compromise entire embedded networks and IoT ecosystems. In environments where Contiki-based devices serve as critical infrastructure components, such as smart meters, industrial sensors, or networked security devices, this vulnerability can result in widespread service outages and operational failures. The vulnerability affects devices that may be deployed in remote locations where physical access is limited, making remote exploitation particularly dangerous as it can render devices permanently inaccessible until manual intervention occurs. Organizations utilizing Contiki 3.0 systems must consider the broader implications for their network security posture, as compromised devices can serve as entry points for more sophisticated attacks or be used to disrupt network communications. The vulnerability also highlights the importance of proper input validation and memory management in embedded systems, where traditional security measures may be insufficient due to resource constraints.
Mitigation strategies for CVE-2021-38386 should prioritize immediate system updates to versions that address the buffer overflow vulnerability, as Contiki 3.0 has been superseded by newer releases with improved memory management and input validation. Organizations should implement network segmentation to limit access to Telnet services and consider disabling the Telnet service entirely in favor of more secure alternatives such as SSH protocols. Additionally, implementing proper input validation mechanisms and buffer size checks within the Telnet service implementation can prevent similar vulnerabilities from occurring in custom or legacy systems. Security monitoring should include detection of unusual directory listing activities that might indicate exploitation attempts, and system administrators should regularly audit file system structures to identify potentially malicious directory configurations. The vulnerability underscores the necessity of following secure coding practices and conducting thorough security testing for embedded systems, particularly those handling user input in networked environments. Organizations should also consider implementing intrusion detection systems to monitor for exploitation attempts and establish incident response procedures specifically addressing denial of service vulnerabilities in embedded systems.