CVE-2016-7563 in MuJS
Summary
by MITRE
The chartorune function in Artifex Software MuJS allows attackers to cause a denial of service (out-of-bounds read) via a * (asterisk) at the end of the input.
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Analysis
by VulDB Data Team • 05/13/2026
The vulnerability identified as CVE-2016-7563 resides within the chartorune function of MuJS, a lightweight javascript engine developed by Artifex Software. This function serves as a critical component for character encoding and decoding operations within the javascript interpreter, processing input strings and converting them into appropriate unicode rune representations. The flaw manifests when the function encounters a specific input pattern consisting of an asterisk character followed by the end of input stream, creating a condition that fundamentally undermines the engine's memory safety mechanisms.
The technical implementation of this vulnerability stems from inadequate bounds checking within the chartorune function's parsing logic. When processing input sequences, the function fails to properly validate the boundary conditions of the input buffer, particularly when encountering special characters like the asterisk at termination points. This omission creates an out-of-bounds memory read scenario where the function attempts to access memory locations beyond the allocated input buffer, resulting in unpredictable behavior and potential system instability. The vulnerability operates at the intersection of buffer management and character encoding processing, making it particularly insidious as it can be triggered through seemingly benign input sequences.
The operational impact of CVE-2016-7563 extends beyond simple denial of service conditions, as it represents a fundamental security weakness that could potentially be exploited for more sophisticated attacks. An attacker capable of controlling input to the MuJS interpreter could leverage this vulnerability to cause application crashes, system instability, or potentially even execute arbitrary code through memory corruption. The out-of-bounds read condition creates opportunities for information disclosure, as adjacent memory contents may be inadvertently exposed during the malformed input processing. This vulnerability directly aligns with CWE-125, which describes out-of-bounds read conditions, and demonstrates the critical importance of proper input validation and bounds checking in interpreter implementations.
Mitigation strategies for this vulnerability require immediate patching of affected MuJS installations, as the flaw exists within core memory management functions that cannot be effectively bypassed through configuration changes. System administrators should prioritize updating to versions that include proper bounds checking and input validation mechanisms for the chartorune function. Additionally, implementing input sanitization at application layers that utilize MuJS can provide defensive measures against exploitation attempts. The vulnerability's characteristics make it particularly relevant to ATT&CK technique T1059.007, which covers javascript and vbscript execution, as attackers could leverage such memory corruption flaws to gain unauthorized access to systems. Organizations should also consider implementing runtime monitoring and intrusion detection systems to identify potential exploitation attempts targeting this specific out-of-bounds read condition.