CVE-2021-46534 in MJS
Summary
by MITRE • 01/28/2022
Cesanta MJS v2.20.0 was discovered to contain a SEGV vulnerability via getprop_builtin_foreign 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-2021-46534 affects Cesanta MJS version 2.20.0, a lightweight JavaScript engine designed for embedded systems and IoT devices. This flaw manifests as a segmentation fault (SEGV) within the getprop_builtin_foreign function located in the src/mjs_exec.c source file, representing a critical stability issue that can be exploited to disrupt system operations. The vulnerability specifically targets the JavaScript engine's property access mechanism when handling foreign objects, creating a scenario where improper memory access can occur during script execution. This type of vulnerability falls under the category of memory corruption issues that can severely impact the reliability of embedded systems relying on MJS for scripting capabilities.
The technical implementation of this vulnerability stems from inadequate input validation and memory management within the getprop_builtin_foreign function. When the JavaScript engine processes property access operations on foreign objects, the function fails to properly validate the object references or handle edge cases in the object structure. This leads to a situation where the engine attempts to access memory locations that are either unmapped or unauthorized, resulting in a segmentation fault that terminates the application process. The flaw demonstrates characteristics consistent with CWE-125, which describes out-of-bounds read vulnerabilities, and CWE-787, which covers out-of-bounds write conditions. The vulnerability can be triggered through malicious JavaScript code that manipulates object properties in ways that exploit the improper validation logic within the engine's execution context.
From an operational standpoint, this vulnerability poses significant risks to embedded systems and IoT devices that utilize Cesanta MJS for scripting functionality. The denial of service condition can render devices inoperable, potentially affecting critical infrastructure applications where system availability is paramount. Attackers could exploit this vulnerability by injecting malicious JavaScript payloads that specifically target the property access mechanisms, causing the affected applications to crash and restart repeatedly. This can lead to extended downtime, service disruption, and potential data loss in mission-critical systems. The vulnerability aligns with ATT&CK technique T1499.004, which covers network denial of service attacks, and represents a common vector for disrupting embedded device operations through software-level exploitation. The impact extends beyond simple service interruption as it can compromise the overall reliability and security posture of IoT deployments that depend on this JavaScript engine for dynamic functionality.
Mitigation strategies for CVE-2021-46534 should prioritize immediate patching of affected systems with the vendor-provided security updates. Organizations must conduct comprehensive inventory assessments to identify all devices running Cesanta MJS version 2.20.0 or earlier, particularly in critical infrastructure environments where the vulnerability could have severe consequences. Network segmentation and access controls should be implemented to limit exposure of vulnerable systems to untrusted network traffic. Additionally, input validation should be strengthened at application boundaries to prevent malicious JavaScript from reaching the vulnerable engine components. System monitoring and intrusion detection systems should be configured to alert on abnormal process termination patterns that may indicate exploitation attempts. The remediation process should include thorough testing of patched systems to ensure that the vulnerability has been properly addressed without introducing regressions in application functionality. Regular security assessments and vulnerability scanning should be conducted to identify similar issues in other embedded systems and scripting engines within the organization's infrastructure.