CVE-2021-46549 in MJS
Summary
by MITRE • 01/28/2022
Cesanta MJS v2.20.0 was discovered to contain a SEGV vulnerability via parse_cval_type at src/mjs_ffi.c. This vulnerability can lead to a Denial of Service (DoS).
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Analysis
by VulDB Data Team • 01/30/2022
The vulnerability identified as CVE-2021-46549 affects Cesanta MJS version 2.20.0, a lightweight JavaScript engine designed for embedded systems and IoT applications. This security flaw resides within the parse_cval_type function located in the src/mjs_ffi.c source file, representing a critical software defect that compromises system stability and availability. The vulnerability manifests as a segmentation fault (SEGV) condition that occurs during the parsing of certain input values within the foreign function interface implementation, which is a core component enabling interaction between JavaScript code and native C libraries.
The technical nature of this vulnerability stems from inadequate input validation and memory management within the JavaScript engine's foreign function interface subsystem. When the parse_cval_type function processes malformed or unexpected input parameters, it fails to properly handle memory access boundaries, leading to unauthorized memory access patterns that trigger system termination. This represents a classic buffer overread or improper memory dereference scenario that aligns with CWE-125 weakness classification for out-of-bounds read conditions. The vulnerability is particularly concerning because it occurs during the parsing phase of JavaScript execution, meaning that any application utilizing Cesanta MJS for embedded scripting could be susceptible to arbitrary code execution or system crashes when processing untrusted input data through the FFI interface.
The operational impact of CVE-2021-46549 extends beyond simple denial of service, as it can potentially enable more sophisticated attacks within embedded environments where Cesanta MJS is deployed. Systems utilizing this JavaScript engine for IoT devices, embedded controllers, or microcontroller applications may experience complete service disruption when malicious input triggers the segmentation fault. The vulnerability's exploitation requires minimal conditions since it can be triggered through normal JavaScript execution flows when FFI functions are invoked with specific parameter combinations. This makes it particularly dangerous in production environments where embedded systems may be exposed to untrusted input sources or remote attackers attempting to disrupt service availability. The DoS condition can affect critical infrastructure components including industrial control systems, network devices, and smart home appliances that rely on embedded JavaScript engines for automation and control functions.
Organizations utilizing Cesanta MJS v2.20.0 should implement immediate mitigation strategies including patching to the latest available version that addresses this vulnerability, as well as implementing input validation controls at application boundaries to prevent malformed data from reaching the vulnerable parsing functions. Network segmentation and monitoring should be enhanced to detect potential exploitation attempts targeting this specific vulnerability. The ATT&CK framework categorizes this issue under T1499.004 for network denial of service, while the underlying memory corruption represents a T1059.007 technique for command and control through script-based execution. Additionally, implementing runtime application self-protection mechanisms and using memory safety features such as stack canaries or address space layout randomization can provide defense-in-depth measures against exploitation attempts. Regular security assessments and vulnerability scanning should include checks for this specific CVE to ensure complete remediation across all embedded systems and IoT devices utilizing the affected JavaScript engine version.