CVE-2021-46524 in MJS
Summary
by MITRE • 01/28/2022
Cesanta MJS v2.20.0 was discovered to contain a heap buffer overflow via snquote at mjs/src/mjs_json.c.
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Analysis
by VulDB Data Team • 01/30/2022
The vulnerability identified as CVE-2021-46524 affects Cesanta MJS version 2.20.0, a lightweight JavaScript engine designed for embedded systems and IoT applications. This heap buffer overflow represents a critical security flaw that could potentially allow attackers to execute arbitrary code or cause denial of service conditions within applications that utilize this JavaScript engine. The vulnerability specifically manifests in the snquote function located within the mjs_json.c source file, which handles JSON string quoting operations. The issue arises when processing malformed JSON input that triggers improper memory allocation during string handling operations.
The technical root cause of this vulnerability stems from inadequate bounds checking within the snquote function implementation. When processing JSON strings, the function fails to properly validate the length of input data against allocated buffer boundaries, creating a condition where heap memory can be overwritten beyond its intended limits. This type of vulnerability falls under CWE-121, which categorizes heap-based buffer overflow conditions, and represents a classic example of improper input validation leading to memory corruption. The flaw occurs during JSON parsing operations when the JavaScript engine attempts to quote strings, particularly when handling special characters or malformed input sequences that exceed expected buffer sizes.
The operational impact of this vulnerability extends beyond simple denial of service scenarios to potentially enable remote code execution in vulnerable applications. Attackers could craft malicious JSON payloads that, when processed by applications using Cesanta MJS v2.20.0, would trigger the buffer overflow condition. This could result in arbitrary code execution on the target system, allowing threat actors to gain unauthorized access, escalate privileges, or completely compromise the affected device. The vulnerability is particularly concerning in IoT and embedded device contexts where these JavaScript engines are commonly deployed, as such devices often lack robust security measures and may be permanently exposed to network threats. The ATT&CK framework categorizes this type of vulnerability under T1203, which covers legitimate programs that can be used for execution, and T1059, which covers command and scripting interpreter techniques.
Mitigation strategies for CVE-2021-46524 should prioritize immediate patching of affected systems to version 2.21.0 or later, which contains the necessary fixes for the heap buffer overflow condition. Organizations should conduct comprehensive inventory assessments to identify all systems utilizing Cesanta MJS v2.20.0 and ensure timely updates are deployed across their infrastructure. Additionally, implementing input validation measures and sanitization protocols can provide defense-in-depth protection against exploitation attempts. Network segmentation and access controls should be reinforced to limit potential attack surfaces, while monitoring systems should be configured to detect anomalous JSON parsing activities that might indicate exploitation attempts. Security teams should also consider implementing runtime protections such as address space layout randomization and stack canaries to make exploitation more difficult, though these measures do not fully address the underlying buffer overflow condition. The vulnerability highlights the importance of proper memory management practices in embedded systems development and underscores the necessity of thorough security testing for all components used in production environments.