CVE-2026-110715 in MuJS
Summary
by MITRE • 10/14/2026
MuJS 1.3.6 before 1.3.9 contains a heap out-of-bounds read and write vulnerability in Array.prototype.sort that allows attackers to corrupt memory by inflating a simple array's length. Attackers can supply JavaScript that enlarges a dense array's length and calls sort, causing Ap_sort_cmp and Ap_sort_swap to access slots past the buffer and crash the process.
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Analysis
by VulDB Data Team • 10/15/2026
The vulnerability identified in MuJS versions prior to 1.3.9 represents a critical memory safety failure within the core JavaScript engine implementation, specifically affecting the Array.prototype.sort method. This flaw is categorized as a heap-based out-of-bounds read and write condition, which falls under CWE-787 (Out-of-Bounds Write) and CWE-125 (Out-of-Bounds Read). The root cause lies in the internal handling of array length properties during sorting operations. When an attacker supplies JavaScript code that artificially inflates the length property of a dense array without correspondingly allocating memory for the new indices, the engine fails to validate bounds before proceeding with the sort algorithm. This discrepancy between the logical size of the array and its actual allocated buffer size creates a dangerous state where subsequent access patterns exceed the boundaries of the allocated heap memory.
During execution, the vulnerability is triggered when the Ap_sort_cmp comparison function or the Ap_sort_swap swapping function attempts to access elements at indices that fall within the inflated but unallocated range. Because these functions do not perform adequate boundary checks against the actual buffer size rather than just the declared length property, they read from and write to arbitrary locations in the heap memory adjacent to the array object. This behavior allows for both information disclosure through out-of-bounds reads and potential code execution or denial of service via out-of-bounds writes. The ability to corrupt memory structures can lead to crashes, as observed when accessing invalid slots causes immediate process termination, but more sophisticated exploitation could allow an attacker to overwrite function pointers or object headers within the JavaScript engine's heap space.
From a threat intelligence perspective, this vulnerability aligns with ATT&CK technique T1203 (Exploitation for Client Execution) if leveraged in a client-side context such as embedded web views, and potentially T1499 (Endpoint Denial of Service) due to the potential for application crashes. The impact extends beyond simple stability issues; memory corruption vulnerabilities are frequently chained with other flaws to achieve arbitrary code execution. In environments where MuJS is used within IoT devices, mobile applications, or server-side JavaScript runtimes, this flaw could be exploited to bypass security controls, inject malicious payloads, or destabilize critical services that rely on the integrity of the underlying runtime environment.
Mitigation strategies primarily involve upgrading to MuJS version 1.3.9 or later, where these bounds checking mechanisms have been corrected to ensure that array operations respect actual memory allocations rather than just declared lengths. For systems unable to immediately upgrade, developers should implement strict input validation on any JavaScript code executed by the engine, particularly regarding dynamic manipulation of array properties. Additionally, enabling heap protection features such as Address Sanitizer during development and deployment can help detect these out-of-bounds accesses early in the software lifecycle. Security teams should also monitor for unusual memory usage patterns or crashes associated with sorting operations within applications utilizing this library to identify potential exploitation attempts in real-time.