CVE-2021-46530 in MJS
Summary
by MITRE • 01/28/2022
Cesanta MJS v2.20.0 was discovered to contain a SEGV vulnerability via mjs_execute at src/mjs_exec.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-2021-46530 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_execute function located in the src/mjs_exec.c source file, representing a critical stability issue that can be exploited to cause system crashes. The vulnerability specifically impacts the JavaScript engine's execution flow when processing certain input sequences, creating a condition where the application fails to handle malformed or unexpected JavaScript code gracefully.
The technical implementation of this vulnerability stems from insufficient input validation and error handling within the JavaScript execution engine. When the mjs_execute function processes specific patterns of JavaScript code, it fails to properly validate the execution context or handle edge cases in the parsing and execution pipeline. This leads to memory access violations where the engine attempts to read or write to protected memory regions, resulting in segmentation faults that terminate the application process. The flaw demonstrates characteristics consistent with CWE-125, which describes out-of-bounds read conditions, and CWE-119, which covers weak buffer access protections, both of which are common in embedded scripting engines where memory constraints and input sanitization become critical factors.
The operational impact of this vulnerability extends beyond simple service disruption as it creates opportunities for denial of service attacks that can affect embedded devices, IoT systems, and applications relying on Cesanta MJS for scripting capabilities. Attackers can craft malicious JavaScript payloads that trigger the segmentation fault, causing the target system to crash and potentially requiring manual intervention for recovery. In environments where these systems are critical for operations, such as industrial control systems or network infrastructure, this vulnerability can result in significant downtime and operational disruption. The vulnerability is particularly concerning in embedded contexts where automatic restart mechanisms may not be available or where system recovery processes are complex and time-consuming.
Mitigation strategies for CVE-2021-46530 should focus on immediate software updates to versions that have addressed the segmentation fault issue in the mjs_execute function. Organizations should implement comprehensive input validation and sanitization measures for all JavaScript code executed within their systems, particularly when processing external or untrusted input. Network segmentation and access controls can help limit exposure by restricting which systems can interact with vulnerable applications. Additionally, implementing application-level monitoring and alerting systems can help detect abnormal behavior patterns that might indicate exploitation attempts. From an ATT&CK framework perspective, this vulnerability aligns with techniques related to privilege escalation and denial of service, specifically T1499.004 for network denial of service and T1059.007 for JavaScript-based execution. Regular security assessments and penetration testing should be conducted to identify similar vulnerabilities in embedded systems and ensure proper patch management procedures are in place across all affected environments.