CVE-2021-46532 in MJS
Summary
by MITRE • 01/28/2022
Cesanta MJS v2.20.0 was discovered to contain a SEGV vulnerability via exec_expr 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-2021-46532 affects Cesanta MJS version 2.20.0, a lightweight JavaScript engine designed for embedded systems and IoT devices. This security flaw resides within the exec_expr function located in the src/mjs_exec.c source file, representing a critical software defect that compromises system stability and availability. The issue manifests as a segmentation fault (SEGV) condition that occurs during expression execution, fundamentally undermining the engine's ability to process JavaScript code safely.
The technical implementation of this vulnerability stems from inadequate input validation and memory management within the JavaScript expression evaluator. When the exec_expr function processes certain malformed or unexpected input sequences, it fails to properly handle memory access boundaries, leading to unauthorized memory dereferencing operations. This flaw operates at the intersection of software robustness and memory safety, creating conditions where legitimate execution paths can trigger system crashes. The vulnerability classification aligns with CWE-125, which describes out-of-bounds read conditions, and CWE-476, which covers null pointer dereference scenarios commonly found in scripting engine implementations.
From an operational perspective, this vulnerability presents significant risks to systems relying on Cesanta MJS for embedded scripting capabilities. The denial of service condition effectively renders affected devices or applications unavailable to legitimate users, potentially disrupting critical operations in IoT deployments, embedded systems, or web applications that depend on this JavaScript engine. Attackers could exploit this weakness to repeatedly crash services, leading to persistent availability issues that may require manual intervention for system recovery. The impact extends beyond simple disruption as compromised systems may become vulnerable to further exploitation attempts, particularly in environments where service availability is paramount for operational continuity.
Mitigation strategies for CVE-2021-46532 should prioritize immediate software updates to versions that address the underlying memory handling issues in the exec_expr function. System administrators must implement comprehensive patch management procedures to ensure all affected instances are updated promptly, as the vulnerability exists in a widely deployed JavaScript engine used across multiple industrial and embedded applications. Additional defensive measures include implementing input sanitization layers, deploying intrusion detection systems to monitor for exploitation attempts, and establishing robust monitoring protocols to detect service availability issues. Organizations should also consider implementing application sandboxing techniques and runtime protections to limit the impact of potential exploitation attempts, aligning with ATT&CK technique T1499.004 for resource exhaustion attacks and T1059.007 for script-based execution methods that could leverage this vulnerability.