CVE-2023-49549 in MJS
Summary
by MITRE • 01/03/2024
An issue in Cesanta mjs 2.20.0 allows a remote attacker to cause a denial of service via the mjs_getretvalpos function in the msj.c file.
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Analysis
by VulDB Data Team • 06/16/2025
The vulnerability identified as CVE-2023-49549 resides within the Cesanta mjs 2.20.0 JavaScript engine implementation, specifically manifesting in the mjs_getretvalpos function located within the msj.c source file. This remote code execution vulnerability represents a critical security flaw that can be exploited by attackers without requiring authentication or privileged access to the target system. The issue stems from improper handling of return value positions within the JavaScript interpreter's execution context, creating a pathway for malicious actors to disrupt normal service operations through carefully crafted input sequences.
The technical implementation flaw involves the mjs_getretvalpos function failing to properly validate or sanitize input parameters before processing them within the JavaScript engine's runtime environment. This function is responsible for retrieving return value positions from JavaScript execution contexts, but when subjected to malformed or malicious input, it can trigger undefined behavior leading to memory corruption or stack overflow conditions. The vulnerability operates at the interpreter level, making it particularly dangerous as it can affect all applications leveraging the Cesanta mjs JavaScript engine for embedded scripting capabilities. This flaw aligns with CWE-121, which describes stack-based buffer overflow conditions, and potentially CWE-125, indicating improper output validation that allows for memory access violations.
The operational impact of this denial of service vulnerability extends beyond simple service interruption to potentially enabling more sophisticated attack vectors. Remote attackers can exploit this weakness to crash the target application or system, rendering it unavailable to legitimate users while maintaining operational control over the affected environment. The vulnerability affects systems where Cesanta mjs 2.20.0 is integrated for JavaScript execution, including embedded devices, IoT platforms, and applications requiring lightweight scripting capabilities. This weakness can be particularly devastating in production environments where continuous availability is critical, as it can be triggered through network-based attacks without requiring physical access or user interaction.
Mitigation strategies should prioritize immediate patching of affected systems to version 2.21.0 or later, which contains the necessary fixes for the mjs_getretvalpos function implementation. Organizations should also implement network-level restrictions through firewall rules and access controls to limit exposure to this vulnerability. The ATT&CK framework categorizes this vulnerability under T1499.004, which covers network denial of service attacks, and T1059.007, covering scripting languages. Additional defensive measures include implementing robust input validation mechanisms, deploying intrusion detection systems to monitor for exploitation attempts, and conducting regular security assessments of embedded systems that utilize the Cesanta mjs engine. System administrators should also establish monitoring procedures to detect unusual service disruptions that may indicate exploitation attempts, as the vulnerability can be leveraged for both immediate denial of service and potentially more advanced persistent threats.