CVE-2021-38387 in Contiki
Summary
by MITRE • 08/11/2021
In Contiki 3.0, a Telnet server that silently quits (before disconnection with clients) leads to connected clients entering an infinite loop and waiting forever, which may cause excessive CPU consumption.
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Analysis
by VulDB Data Team • 08/15/2021
The vulnerability identified as CVE-2021-38387 resides within Contiki 3.0, a popular operating system for embedded devices and Internet of Things applications. This issue manifests through the Telnet server component which exhibits problematic behavior during client disconnection processes. The flaw creates a scenario where the Telnet server terminates its connection handling routine prematurely without properly notifying connected clients of the disconnection event. This silent termination creates a critical condition that affects the client-side connection management and results in a denial of service scenario.
The technical root cause of this vulnerability stems from improper handling of connection lifecycle events within the Telnet server implementation. When the server process terminates before completing the disconnection sequence, connected clients remain in a state of indefinite waiting for proper connection closure signals. This condition creates a resource exhaustion scenario where client applications become stuck in continuous polling or waiting loops, consuming CPU cycles unnecessarily while attempting to maintain connections that have already been terminated server-side. The vulnerability specifically targets the communication protocol handling mechanisms that govern how Telnet connections are managed and terminated.
The operational impact of this vulnerability extends beyond simple resource consumption, creating potential system instability and service disruption in embedded environments where Contiki 3.0 is deployed. Connected clients experiencing this issue may become unresponsive to other commands or system events, effectively rendering the device or application unusable. The infinite loop condition consumes CPU resources that could otherwise be allocated to legitimate system processes, potentially leading to complete system hang conditions in resource-constrained embedded devices. This vulnerability particularly affects IoT deployments where multiple devices maintain Telnet connections for monitoring or management purposes.
From a cybersecurity perspective, this vulnerability aligns with CWE-400, which addresses unspecified resource exhaustion conditions, and represents a denial of service scenario that can be exploited to consume system resources. The ATT&CK framework categorizes this under T1499.004, which deals with network denial of service attacks, as the vulnerability enables an attacker to consume system resources through improper connection handling. The flaw can be exploited by an attacker who maintains a Telnet connection to a device running Contiki 3.0 and then triggers the server termination process, causing connected clients to enter the problematic infinite loop state. Mitigation strategies should include implementing proper connection termination protocols, adding timeout mechanisms for client waiting states, and ensuring that all disconnection events are properly communicated to connected clients. Additionally, system administrators should consider upgrading to newer versions of Contiki that have addressed this specific connection handling issue, as the vulnerability demonstrates poor resource management practices that could be exploited in broader attack scenarios.