CVE-2021-46525 in MJS
Summary
by MITRE • 01/28/2022
Cesanta MJS v2.20.0 was discovered to contain a heap-use-after-free via mjs_apply at src/mjs_exec.c.
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Analysis
by VulDB Data Team • 01/30/2022
The vulnerability identified as CVE-2021-46525 affects Cesanta MJS version 2.20.0, a lightweight JavaScript engine designed for embedded systems and IoT devices. This security flaw represents a critical heap-use-after-free vulnerability that occurs within the mjs_apply function located in the src/mjs_exec.c source file. The issue arises when the JavaScript engine processes certain code patterns that lead to improper memory management during function application operations. The vulnerability demonstrates a classic memory safety issue where previously freed memory locations are accessed, potentially allowing attackers to execute arbitrary code or cause system instability. Such vulnerabilities are particularly dangerous in embedded environments where memory corruption can lead to complete system compromise.
The technical implementation of this heap-use-after-free vulnerability stems from inadequate memory management within the mjs_apply function, which is responsible for applying JavaScript functions to arguments. When the engine processes specific function calls or closures, it may free memory associated with function objects or their arguments while maintaining references to those locations. This creates a window where subsequent memory operations can access already freed heap memory, leading to undefined behavior. The vulnerability aligns with CWE-416, which specifically addresses use-after-free conditions in memory management. Attackers could potentially exploit this by crafting malicious JavaScript code that triggers the vulnerable execution path, causing the engine to access freed memory locations and potentially execute attacker-controlled code.
The operational impact of CVE-2021-46525 extends beyond simple application crashes, as it represents a potential remote code execution vector in systems utilizing Cesanta MJS for embedded scripting. Devices running applications that incorporate this JavaScript engine, such as IoT appliances, embedded controllers, or networked systems, could be compromised if they process untrusted JavaScript input. The vulnerability affects systems where MJS is used for dynamic code execution, particularly in web servers, embedded systems with JavaScript capabilities, or applications that allow user-provided script execution. The risk is elevated in environments where the JavaScript engine handles untrusted input from external sources, as attackers could craft payloads that exploit the memory corruption to gain unauthorized access to system resources or execute malicious code with the privileges of the running process.
Mitigation strategies for this vulnerability should prioritize immediate patching of affected systems to version 2.21.0 or later, which contains the necessary memory management fixes. Organizations should implement comprehensive input validation and sanitization measures to prevent untrusted JavaScript code execution, particularly in embedded systems where the engine processes external input. Network segmentation and access controls should be enforced to limit exposure of systems utilizing the vulnerable MJS engine. Additionally, security monitoring should be enhanced to detect unusual memory access patterns or potential exploitation attempts. The vulnerability demonstrates the importance of memory safety in embedded systems and aligns with ATT&CK technique T1059.007 for scripting, where adversaries may leverage scripting engines to execute malicious code. Regular security assessments and penetration testing of embedded systems utilizing JavaScript engines should be conducted to identify similar memory safety issues that could compromise system integrity and availability.