CVE-2021-46523 in MJS
Summary
by MITRE • 01/28/2022
Cesanta MJS v2.20.0 was discovered to contain a heap buffer overflow via to_json_or_debug at mjs/src/mjs_json.c.
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Analysis
by VulDB Data Team • 01/30/2022
The heap buffer overflow vulnerability identified in Cesanta MJS version 2.20.0 represents a critical security flaw that can lead to arbitrary code execution and system compromise. This vulnerability specifically manifests within the to_json_or_debug function located in the mjs/src/mjs_json.c source file, where improper memory handling allows attackers to manipulate heap memory through crafted input data. The flaw stems from insufficient bounds checking during JSON serialization operations, creating a pathway for memory corruption that can be exploited by malicious actors.
The technical implementation of this vulnerability involves the manipulation of input data that flows through the JSON processing pipeline, where the to_json_or_debug function fails to validate the size of buffer allocations before writing data to heap memory. This type of flaw falls under the Common Weakness Enumeration category of CWE-121, which describes stack-based buffer overflow conditions, though in this case the vulnerability specifically affects heap memory allocation. The vulnerability can be triggered when the MJS interpreter processes malformed JSON data that causes the function to write beyond allocated memory boundaries, potentially leading to memory corruption that affects program execution flow.
Operational impact assessment reveals that this vulnerability poses significant risks to systems utilizing Cesanta MJS for embedded scripting applications, web servers, or IoT devices that rely on the interpreter for dynamic content processing. Attackers can exploit this flaw to execute arbitrary code with the privileges of the affected process, potentially leading to complete system compromise. The vulnerability's exploitation requires minimal prerequisites, making it particularly dangerous in environments where the interpreter handles untrusted input data from external sources. Systems running vulnerable versions may experience denial of service conditions, data corruption, or unauthorized access to sensitive information, with potential for privilege escalation depending on the execution context.
Mitigation strategies for this vulnerability include immediate deployment of the patched version of Cesanta MJS, which addresses the buffer overflow through proper bounds checking and memory allocation validation. Organizations should implement input validation mechanisms to sanitize all JSON data before processing, particularly when dealing with external or user-provided inputs. Network segmentation and access controls can help limit the potential impact of exploitation attempts, while regular security audits and penetration testing should be conducted to identify similar vulnerabilities in the broader software ecosystem. The ATT&CK framework categorizes this type of vulnerability under T1059.007 for application layer execution and T1203 for exploitation for privilege escalation, highlighting the multi-faceted nature of potential attack vectors that leverage such memory corruption flaws.