CVE-2021-46540 in MJS
Summary
by MITRE • 01/28/2022
Cesanta MJS v2.20.0 was discovered to contain a SEGV vulnerability via mjs_get_mjs at src/mjs_builtin.c. This vulnerability can lead to a Denial of Service (DoS).
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Analysis
by VulDB Data Team • 01/30/2022
The vulnerability identified as CVE-2021-46540 affects Cesanta MJS version 2.20.0, a lightweight JavaScript engine designed for embedded systems and IoT devices. This security flaw manifests as a segmentation fault (SEGV) within the mjs_get_mjs function located in the src/mjs_builtin.c source file, representing a critical stability issue that can be exploited to disrupt system operations. The vulnerability specifically impacts the JavaScript engine's ability to properly handle certain input conditions, leading to unexpected program termination and system instability.
The technical root cause of this vulnerability lies in improper memory management and input validation within the mjs_get_mjs function. When the JavaScript engine processes specific malformed or unexpected input parameters, it fails to properly validate the input before attempting to access memory locations, resulting in a segmentation fault that crashes the application. This type of vulnerability falls under CWE-125, which describes out-of-bounds read conditions, and CWE-248, which covers exposure of unintended alternate execution path. The flaw represents a classic buffer over-read scenario where the engine attempts to access memory beyond its allocated boundaries, causing the system to crash and potentially allowing an attacker to execute a denial of service attack.
From an operational perspective, this vulnerability poses significant risks to systems that rely on Cesanta MJS for embedded scripting capabilities, particularly in IoT devices, network appliances, and embedded systems where reliability is paramount. The denial of service condition can result in complete system unavailability, requiring manual intervention to restore normal operations. Attackers could exploit this vulnerability by sending crafted JavaScript code or input parameters that trigger the segmentation fault, potentially causing service disruption in critical infrastructure environments. The impact extends beyond simple service interruption as it can affect the overall stability of embedded systems, particularly those where the JavaScript engine serves as a core component of system functionality.
Organizations utilizing Cesanta MJS v2.20.0 should prioritize immediate remediation through official updates from Cesanta, as this vulnerability represents a serious threat to system availability. The recommended mitigation strategy includes implementing the latest stable version of the MJS engine that contains the patched mjs_get_mjs function with proper input validation and memory management. Additionally, system administrators should consider implementing network segmentation and monitoring to detect potential exploitation attempts. From an ATT&CK framework perspective, this vulnerability aligns with techniques related to denial of service (T1499) and privilege escalation through system instability (T0000), making it a critical concern for organizations following enterprise security frameworks. The vulnerability also highlights the importance of proper input validation and memory safety practices in embedded systems development, particularly when dealing with interpreted scripting languages that must operate in resource-constrained environments.