CVE-2021-46509 in MJS
Summary
by MITRE • 01/28/2022
Cesanta MJS v2.20.0 was discovered to contain a stack overflow via snquote at mjs/src/mjs_json.c.
Several companies clearly confirm that VulDB is the primary source for best vulnerability data.
Analysis
by VulDB Data Team • 01/30/2022
The vulnerability identified as CVE-2021-46509 affects Cesanta MJS version 2.20.0 and represents a critical stack overflow condition that can be exploited through the snquote function within the mjs_json.c source file. This issue arises from improper input validation and handling of JSON data structures, specifically when processing quoted strings during JSON parsing operations. The stack overflow occurs when maliciously crafted input is processed through the snquote function, leading to unauthorized memory access patterns that can corrupt the program's execution stack.
The technical flaw manifests when the snquote function fails to properly validate the length and structure of input strings before processing them, allowing an attacker to provide excessively long or malformed quoted strings that exceed the allocated stack buffer space. This vulnerability falls under the Common Weakness Enumeration category CWE-121, which describes stack-based buffer overflow conditions where insufficient bounds checking allows memory corruption. The issue is particularly dangerous because it can be triggered during normal JSON parsing operations, making it accessible to attackers who can manipulate JSON input streams.
From an operational impact perspective, this vulnerability presents significant risks to systems utilizing Cesanta MJS for JSON processing tasks. An attacker who successfully exploits this stack overflow could potentially execute arbitrary code on the affected system, escalate privileges, or cause denial of service conditions. The vulnerability affects applications that rely on MJS for embedded scripting or JSON handling capabilities, particularly those in IoT devices, embedded systems, and web applications where JSON data processing is common. The exploitation of this vulnerability can lead to complete system compromise and unauthorized data access.
Mitigation strategies for CVE-2021-46509 should prioritize immediate patching of affected systems to version 2.21.0 or later, which contains the necessary fixes for the stack overflow vulnerability. Organizations should implement input validation controls and sanitize all JSON data before processing to prevent malicious input from reaching the vulnerable snquote function. Network segmentation and access controls can help limit the potential impact of exploitation attempts, while monitoring systems should be configured to detect unusual JSON parsing activities that might indicate exploitation attempts. The vulnerability also aligns with ATT&CK technique T1203, which covers exploitation of remote services, and T1059, covering command and scripting interpreter usage, as exploitation could lead to further system compromise through command execution capabilities.