CVE-2021-29329 in OpenSource
Summary
by MITRE • 11/19/2021
OpenSource Moddable v10.5.0 was discovered to contain a stack overflow in the fxBinaryExpressionNodeDistribute function at /moddable/xs/sources/xsTree.c.
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Analysis
by VulDB Data Team • 11/22/2021
The vulnerability identified as CVE-2021-29329 represents a critical stack overflow condition within the OpenSource Moddable v10.5.0 runtime environment. This issue manifests in the fxBinaryExpressionNodeDistribute function located within the xsTree.c source file, which forms part of the Moddable XS scripting engine used for embedded application development. The Moddable platform is widely utilized for creating IoT applications and embedded systems where memory constraints and security considerations are paramount. The stack overflow vulnerability arises from insufficient input validation and recursive processing within the expression distribution logic, creating a potential pathway for arbitrary code execution or system instability.
The technical flaw stems from the function's handling of binary expression nodes during code compilation and execution phases. When processing complex nested expressions, the fxBinaryExpressionNodeDistribute function fails to properly limit recursive calls or validate stack depth, leading to excessive stack consumption. This condition typically occurs when developers create deeply nested mathematical or logical expressions that trigger the recursive processing path. The vulnerability is classified as a CWE-129 Improper Validation of Array Index, specifically manifesting as a stack-based buffer overflow through recursive function calls. The flaw demonstrates characteristics consistent with CWE-770 Allocation of Resources Without Limits or Throttling, where the system fails to enforce resource consumption limits during expression parsing operations.
The operational impact of this vulnerability extends beyond simple system crashes, potentially enabling remote code execution in environments where untrusted input is processed through the Moddable runtime. Attackers could exploit this weakness by crafting malicious scripts containing deeply nested expressions that trigger the vulnerable code path, leading to stack exhaustion and subsequent system compromise. This vulnerability particularly affects embedded systems and IoT devices running Moddable applications, where recovery mechanisms may be limited and system availability is critical. The attack surface includes any application that utilizes the Moddable XS engine for dynamic script execution, including smart home devices, industrial control systems, and mobile applications. According to ATT&CK framework category T1203 Exploitation for Client Execution, this vulnerability could enable adversaries to execute malicious code within the target environment, while T1499.004 Endpoint Denial of Service represents the potential for system instability and denial of service conditions.
Mitigation strategies for CVE-2021-29329 should prioritize immediate patching of the Moddable runtime to version 10.5.1 or later, which includes proper bounds checking and stack depth limitations. Organizations should implement input sanitization measures to prevent deeply nested expressions from reaching the vulnerable function, particularly in environments processing untrusted scripts. Memory protection mechanisms such as stack canaries and address space layout randomization should be enabled where possible. Additionally, monitoring systems should be deployed to detect unusual stack consumption patterns that might indicate exploitation attempts. The vulnerability highlights the importance of secure coding practices in embedded environments and underscores the need for comprehensive input validation in interpreted languages. Security teams should conduct thorough code reviews of any custom Moddable applications to identify similar patterns that might create additional attack vectors. Regular vulnerability assessments and penetration testing should be performed on systems utilizing the Moddable platform to identify and remediate similar issues before they can be exploited in production environments.