CVE-2020-36372 in MJS
Summary
by MITRE • 05/29/2021
Stack overflow vulnerability in parse_plus_minus Cesanta MJS 1.20.1, allows remote attackers to cause a Denial of Service (DoS) via a crafted file.
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Analysis
by VulDB Data Team • 06/03/2021
The CVE-2020-36372 vulnerability represents a critical stack overflow issue discovered in Cesanta MJS version 1.20.1, a lightweight JavaScript engine designed for embedded systems and IoT devices. This vulnerability resides within the parse_plus_minus function, which is responsible for parsing mathematical expressions containing plus and minus operators. The flaw manifests when the JavaScript engine processes specially crafted input files that trigger excessive stack consumption during the parsing phase, ultimately leading to a stack buffer overflow condition that can be exploited by remote attackers.
The technical implementation of this vulnerability stems from inadequate input validation and stack memory management within the MJS parser. When the parse_plus_minus function encounters malformed or excessively nested mathematical expressions, it fails to properly limit the recursion depth or stack allocation, allowing malicious input to consume excessive stack space. This behavior aligns with CWE-129, which addresses improper handling of length parameters in input validation, and CWE-787, which covers out-of-bounds write operations that can occur through stack overflow conditions. The vulnerability operates at the application layer and can be classified under ATT&CK technique T1499.004, specifically targeting network denial of service through resource exhaustion.
The operational impact of this vulnerability extends beyond simple denial of service, as it can be leveraged by attackers to crash applications or potentially execute arbitrary code depending on the target system's memory layout and security mitigations. Embedded systems and IoT devices running Cesanta MJS are particularly vulnerable since these environments often lack robust memory protection mechanisms and may not implement stack canaries or other modern exploit mitigations. The vulnerability's remote exploitation capability means that attackers can trigger the condition without physical access to the target device, making it especially dangerous in networked environments where these JavaScript engines are used to process user-supplied content or configuration files.
Organizations utilizing Cesanta MJS 1.20.1 should implement immediate mitigations including updating to the latest version where the vulnerability has been patched, implementing input validation and sanitization measures to prevent malformed expressions from reaching the parser, and deploying network segmentation to limit exposure. Additionally, system administrators should consider implementing stack protection mechanisms such as stack canaries, address space layout randomization, and heap metadata protection. The vulnerability highlights the importance of proper memory management in embedded systems and underscores the need for thorough input validation in all parsing functions, particularly those handling mathematical expressions or scripting languages. Organizations should also consider implementing intrusion detection systems that can identify patterns associated with this specific vulnerability type to detect potential exploitation attempts.