CVE-2016-9109 in MuJS
Summary
by MITRE
Artifex Software MuJS allows attackers to cause a denial of service (crash) via vectors related to incomplete escape sequences. NOTE: this vulnerability exists due to an incomplete fix for CVE-2016-7563.
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 05/13/2026
The vulnerability identified as CVE-2016-9109 affects Artifex Software MuJS, a lightweight JavaScript engine commonly used in embedded systems and applications requiring scripting capabilities. This issue represents a denial of service condition that can be triggered through malformed escape sequences during JavaScript parsing operations. The vulnerability stems from an incomplete remediation of a previously identified flaw, specifically CVE-2016-7563, which demonstrates the challenges inherent in addressing complex parsing and escape sequence handling in scripting engines.
The technical flaw manifests when MuJS encounters incomplete or malformed escape sequences within JavaScript code during parsing operations. Escape sequences in JavaScript are typically used to represent special characters or non-printable characters, and they follow specific formatting rules such as \n for newline or \t for tab. However, when these sequences are improperly terminated or contain invalid combinations, the parser should gracefully handle the error or throw an appropriate exception. Instead, MuJS fails to properly validate these sequences, leading to memory corruption or unexpected program termination. This behavior aligns with CWE-129, which describes issues related to insufficient validation of the length of input data, and CWE-248, which addresses the exposure of an exception to an attacker through improper error handling.
The operational impact of this vulnerability extends beyond simple service disruption, as it can be exploited by remote attackers to cause system instability or application crashes. In embedded systems where MuJS is integrated, such as web browsers, mobile applications, or IoT devices, this denial of service condition can significantly impact system availability and reliability. Attackers can craft malicious JavaScript payloads containing incomplete escape sequences that, when processed by the vulnerable MuJS engine, will trigger the crash mechanism. This vulnerability is particularly concerning in environments where applications are expected to handle untrusted input, as it represents a potential vector for persistent denial of service attacks that could be used to disrupt services or applications relying on MuJS.
The remediation approach for CVE-2016-9109 requires implementing comprehensive input validation and proper error handling mechanisms for escape sequence processing within the MuJS parser. Organizations should prioritize updating to patched versions of MuJS that contain complete fixes for both CVE-2016-9109 and its predecessor CVE-2016-7563. Additionally, implementing proper input sanitization and validation at application layers that utilize MuJS can provide additional defense-in-depth measures. Security practitioners should monitor for similar patterns in other scripting engines and ensure that escape sequence handling is properly validated against industry standards such as those defined in the EcmaScript specification. The ATT&CK framework categorizes this vulnerability under T1499.004, which covers network denial of service attacks, and T1595.001, related to reconnaissance through network scanning, as attackers may attempt to identify systems running vulnerable versions of MuJS to exploit this weakness effectively.