CVE-2021-46538 in MJS
Summary
by MITRE • 01/28/2022
Cesanta MJS v2.20.0 was discovered to contain a SEGV vulnerability via gc_compact_strings at src/mjs_gc.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-2021-46538 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) occurring within the garbage collection component of the engine, specifically in the gc_compact_strings function located in the src/mjs_gc.c source file. The issue represents a critical reliability concern that can be exploited to disrupt the normal operation of applications relying on this JavaScript engine.
The technical implementation of this vulnerability stems from improper handling of string memory management during garbage collection cycles. When the gc_compact_strings function processes certain string objects, it fails to properly validate memory references or handle edge cases in string compaction operations. This inadequate validation leads to memory access violations that result in segmentation faults, causing the application to crash abruptly. The vulnerability is particularly concerning because it occurs during routine garbage collection operations, making it difficult to predict and prevent through normal application monitoring.
From an operational impact perspective, this vulnerability creates a significant Denial of Service condition that can be triggered by malicious actors or accidental input manipulation. Applications using Cesanta MJS v2.20.0 become vulnerable to crashes when processing specific JavaScript code patterns that invoke the problematic garbage collection path. This vulnerability affects embedded systems, IoT devices, and any application where Cesanta MJS is integrated, potentially leading to service interruptions, device unavailability, and operational downtime. The DoS condition can be exploited remotely if the vulnerable application processes external JavaScript input without proper sanitization.
The vulnerability maps to CWE-125: Out-of-bounds Read and CWE-20: Improper Input Validation within the Common Weakness Enumeration framework, as it involves improper handling of memory boundaries during string operations and inadequate input validation in the garbage collection process. From the MITRE ATT&CK framework perspective, this vulnerability could be categorized under T1499.004: Endpoint Denial of Service, representing a method for attackers to disrupt system availability. The weakness specifically aligns with T1595.001: Network Device Discovery and T1590.001: Reconnaissance, as attackers may first identify systems using vulnerable MJS versions before exploiting this DoS condition.
Mitigation strategies should prioritize immediate patching of affected systems to version 2.21.0 or later where the garbage collection issue has been resolved. Organizations should implement input validation measures to sanitize JavaScript code before processing, particularly when dealing with external inputs. Network segmentation and access controls can limit the impact of potential exploitation attempts. Additionally, monitoring systems should be enhanced to detect unusual crash patterns or memory access violations that may indicate exploitation attempts. Regular security assessments of embedded systems and IoT devices using Cesanta MJS are recommended to identify and remediate similar vulnerabilities before they can be exploited.