CVE-2021-41862 in AviatorScript
Summary
by MITRE • 10/02/2021
AviatorScript through 5.2.7 allows code execution via an expression that is encoded with Byte Code Engineering Library (BCEL).
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Analysis
by VulDB Data Team • 10/08/2021
CVE-2021-41862 represents a critical code execution vulnerability in AviatorScript versions 5.2.7 and earlier, where the interpreter fails to properly validate or sanitize expressions that are encoded using the Byte Code Engineering Library BCEL. This vulnerability stems from insufficient input validation mechanisms within the AviatorScript runtime environment, which processes expressions that are serialized using BCEL bytecode format. The flaw allows attackers to craft malicious expressions that, when processed by the interpreter, can execute arbitrary code on the target system. The vulnerability is particularly dangerous because BCEL is commonly used for bytecode manipulation and analysis, making it a legitimate component that bypasses typical security controls. This issue maps to CWE-94, which describes "Improper Control of Generation of Code" and aligns with ATT&CK technique T1059.007 for "Command and Scripting Interpreter: JavaScript", as the vulnerability enables arbitrary code execution through script processing. The technical implementation involves the AviatorScript engine's failure to properly isolate or validate bytecode constructs that are passed through BCEL-encoded expressions, allowing attackers to inject malicious bytecode sequences that get executed within the interpreter's context. This creates a path for remote code execution where an attacker can leverage the legitimate BCEL functionality to bypass security restrictions and execute arbitrary commands on the affected system. The operational impact is severe as this vulnerability can be exploited remotely without authentication, potentially allowing attackers to gain full system control, escalate privileges, or establish persistence mechanisms. The vulnerability affects environments where AviatorScript is used to process user-supplied expressions or data that may contain BCEL-encoded content, particularly in web applications, scripting environments, or any system that accepts and processes external expressions. Organizations using affected versions should immediately upgrade to patched releases and implement input validation controls to prevent the processing of untrusted bytecode content. Additionally, network segmentation and monitoring for suspicious expression processing activities can help detect potential exploitation attempts, while regular security assessments should verify that no legacy systems remain vulnerable to this class of attack. The vulnerability demonstrates the importance of proper sandboxing and input validation in interpreted environments where external libraries with bytecode manipulation capabilities are integrated into the processing pipeline.