CVE-2016-7564 in MuJS
Summary
by MITRE
Heap-based buffer overflow in the Fp_toString function in jsfunction.c in Artifex Software MuJS allows attackers to cause a denial of service (crash) via crafted input.
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Analysis
by VulDB Data Team • 05/13/2026
The vulnerability identified as CVE-2016-7564 represents a critical heap-based buffer overflow within the MuJS JavaScript interpreter developed by Artifex Software. This flaw exists specifically within the Fp_toString function located in the jsfunction.c source file, making it a significant security concern for any system utilizing this JavaScript engine. The buffer overflow occurs when the function processes crafted input data, creating an exploitable condition that can be leveraged by malicious actors to disrupt system operations.
The technical nature of this vulnerability stems from improper bounds checking within the Fp_toString function implementation. When MuJS encounters malformed input during string conversion operations, the heap memory allocation fails to properly validate the input size against the allocated buffer space. This memory management flaw allows attackers to write data beyond the intended buffer boundaries, potentially corrupting adjacent heap memory structures. The vulnerability manifests as a crash condition that can be reliably triggered through carefully constructed input sequences, making it particularly dangerous in environments where MuJS is used to process untrusted data.
From an operational perspective, this vulnerability creates substantial risk for systems that rely on MuJS for embedded scripting capabilities or web application functionality. The denial of service impact means that attackers can intentionally crash applications using the JavaScript interpreter, potentially leading to service disruption for legitimate users. The heap corruption aspect of this vulnerability also opens possibilities for more sophisticated attacks, though the current exploitation is primarily focused on crash conditions. Organizations deploying MuJS in production environments face significant risk if this vulnerability remains unpatched, particularly in web-facing applications or systems processing user-generated content.
The vulnerability aligns with CWE-121, which describes heap-based buffer overflow conditions, and represents a classic example of improper input validation in memory management operations. From an attack framework perspective, this issue maps to multiple ATT&CK techniques including TA0005 (Defense Evasion) through process injection methods and TA0008 (Impact) through service disruption. The exploitability of this vulnerability is enhanced by the fact that it requires minimal complexity to trigger, making it attractive to attackers seeking reliable denial of service attacks. Organizations should prioritize patching this vulnerability as part of their vulnerability management processes, particularly in environments where MuJS is integrated into critical applications or services. The recommended mitigation approach includes immediate deployment of the vendor-provided security update and implementation of input validation measures to prevent malformed data from reaching the vulnerable function.