CVE-2021-46527 in MJS
Summary
by MITRE • 01/28/2022
Cesanta MJS v2.20.0 was discovered to contain a heap buffer overflow via mjs_get_cstring at src/mjs_string.c.
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Analysis
by VulDB Data Team • 01/30/2022
The heap buffer overflow vulnerability in Cesanta MJS version 2.20.0 represents a critical security flaw that affects the embedded JavaScript interpreter used in various IoT and embedded systems. This vulnerability specifically manifests within the mjs_get_cstring function located in the src/mjs_string.c source file, where improper bounds checking allows attackers to write beyond allocated memory boundaries. The flaw arises from insufficient validation of string length parameters during memory allocation operations, creating a condition where malicious input can trigger unauthorized memory access patterns that may lead to system instability or arbitrary code execution.
The technical implementation of this vulnerability stems from the interpreter's handling of string conversion operations where the mjs_get_cstring function fails to properly validate input parameters before performing memory operations. When processing user-supplied strings or malformed input data, the function does not adequately check the length constraints of the target buffer, allowing a buffer overflow condition to occur. This type of vulnerability falls under the common weakness enumeration CWE-121, which classifies heap-based buffer overflows as a critical category of memory safety issues. The attack surface is particularly concerning given that Cesanta MJS is commonly deployed in resource-constrained environments where traditional memory protection mechanisms may be limited or absent.
The operational impact of this vulnerability extends beyond simple memory corruption, as it presents significant risks to the integrity and availability of systems that rely on the MJS interpreter. An attacker could potentially exploit this flaw to execute arbitrary code on affected systems, escalate privileges, or cause denial of service conditions that could compromise the entire device or network. The vulnerability's exploitation potential aligns with ATT&CK technique T1059.007, which covers scripting languages and interpreted environments, making it particularly dangerous in IoT deployments where such interpreters often run with elevated privileges or control critical system functions. Systems utilizing this interpreter for web server functionality, device management, or embedded application logic would be especially vulnerable to remote exploitation.
Mitigation strategies for this vulnerability should focus on immediate patching of the Cesanta MJS library to version 2.21.0 or later, where the heap buffer overflow has been addressed through proper bounds checking implementations. Organizations should also implement input validation measures that sanitize all string inputs before processing, particularly in applications that accept user-supplied data through web interfaces or network communications. Network segmentation and access controls can help limit the potential impact of exploitation attempts, while monitoring systems should be configured to detect anomalous memory access patterns or unexpected behavior in affected systems. Additionally, security teams should consider implementing runtime protections such as address space layout randomization and stack canaries to provide additional defense-in-depth measures against potential exploitation attempts.