CVE-2017-5627 in MuJS
Summary
by MITRE
An issue was discovered in Artifex Software, Inc. MuJS before 4006739a28367c708dea19aeb19b8a1a9326ce08. The jsR_setproperty function in jsrun.c lacks a check for a negative array length. This leads to an integer overflow in the js_pushstring function in jsrun.c when parsing a specially crafted JS file.
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Analysis
by VulDB Data Team • 05/17/2026
The vulnerability identified as CVE-2017-5627 resides within the MuJS JavaScript engine developed by Artifex Software, Inc., specifically affecting versions prior to commit 4006739a28367c708dea19aeb19b8a1a9326ce08. This flaw manifests in the jsR_setproperty function located within the jsrun.c source file, where the absence of validation for negative array length parameters creates a critical security gap. The issue stems from inadequate input sanitization during JavaScript parsing operations, particularly when handling malformed array declarations that could be embedded within maliciously crafted JavaScript files. The vulnerability operates at the intersection of memory management and integer arithmetic within the JavaScript engine's runtime environment, creating conditions where normal operational parameters can be manipulated to trigger unexpected behavior.
The technical exploitation of this vulnerability occurs through a specific code path involving the js_pushstring function in jsrun.c, which processes string operations during JavaScript parsing. When a maliciously constructed JavaScript file contains an array with a negative length value, the engine fails to validate this parameter before proceeding with memory allocation calculations. This oversight results in an integer overflow condition that can corrupt memory structures and potentially allow arbitrary code execution. The vulnerability demonstrates characteristics consistent with CWE-190, Integer Overflow or Wraparound, where the improper handling of integer values leads to memory corruption. The flaw represents a classic buffer overflow scenario where the engine's failure to validate array dimensions creates a predictable overflow condition that can be leveraged by attackers to manipulate memory layout.
The operational impact of this vulnerability extends beyond simple code execution, as it can enable attackers to perform arbitrary code injection within applications that utilize the MuJS engine for JavaScript processing. Systems relying on MuJS for embedded scripting capabilities, including web applications, mobile platforms, and server-side environments, become susceptible to remote code execution attacks. The vulnerability's exploitation potential aligns with ATT&CK technique T1059.007 for JavaScript and T1566.001 for Phishing with Malicious Attachments, as attackers can craft malicious JavaScript files that trigger the overflow condition when processed by vulnerable applications. This creates a significant risk for enterprise environments where JavaScript engines are used for dynamic content processing, particularly in contexts where user-supplied JavaScript content is accepted without proper sanitization.
Mitigation strategies for CVE-2017-5627 require immediate patching of affected MuJS versions to the fixed commit referenced in the vulnerability description. Organizations should implement comprehensive input validation measures to prevent malformed JavaScript content from reaching the parsing engine, particularly when processing untrusted user inputs or external content. Network segmentation and application whitelisting can help reduce the attack surface by limiting which systems can access vulnerable applications. Security monitoring should focus on detecting unusual JavaScript parsing patterns and memory allocation behaviors that could indicate exploitation attempts. Additionally, implementing robust sandboxing mechanisms around JavaScript execution environments can provide defense-in-depth protection against potential exploitation attempts. The vulnerability underscores the importance of proper integer validation in memory management operations and highlights the critical need for thorough security testing of scripting engine components, particularly in environments where JavaScript execution is a core functionality.