CVE-2017-5400 in Firefox
Summary
by MITRE
JIT-spray targeting asm.js combined with a heap spray allows for a bypass of ASLR and DEP protections leading to potential memory corruption attacks. This vulnerability affects Firefox < 52, Firefox ESR < 45.8, Thunderbird < 52, and Thunderbird < 45.8.
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Analysis
by VulDB Data Team • 11/26/2025
The vulnerability identified as CVE-2017-5400 represents a sophisticated exploitation technique that leverages JavaScript Just-In-Time compilation mechanisms to circumvent modern memory protection schemes. This flaw specifically targets the interaction between asm.js execution and heap memory management within Mozilla Firefox and Thunderbird browsers, creating a pathway for attackers to bypass critical security mitigations. The vulnerability operates through a dual-pronged approach that combines JIT-spray and heap spray techniques to achieve memory layout manipulation.
The technical implementation of this vulnerability exploits the JavaScript engine's Just-In-Time compilation process, particularly focusing on how asm.js code is handled within the Firefox browser environment. When the browser processes asm.js code, it generates machine code that gets placed in memory locations that can be manipulated through the heap spray technique. The JIT-spray component creates numerous JavaScript objects with specific memory layouts, while the heap spray technique fills memory with predictable data patterns. This combination allows attackers to predict memory addresses and overcome Address Space Layout Randomization protections that typically prevent memory corruption attacks.
The operational impact of CVE-2017-5400 extends beyond simple privilege escalation, as it enables attackers to execute arbitrary code within the browser context with elevated privileges. This vulnerability directly targets the memory management subsystems of affected browsers, allowing exploitation of memory corruption vulnerabilities that would otherwise be protected by DEP (Data Execution Prevention) mechanisms. The attack vector specifically targets the Firefox JavaScript engine's handling of asm.js code, which creates a unique opportunity for attackers to manipulate memory layout and bypass security protections. This vulnerability affects not only the main Firefox browser but also Thunderbird email client, indicating a widespread impact across Mozilla's browser ecosystem.
This exploitation technique aligns with several ATT&CK framework concepts including T1059.007 for JavaScript execution and T1068 for local privilege escalation through memory corruption. The vulnerability demonstrates characteristics consistent with CWE-119 which addresses memory corruption issues, and CWE-121 which deals with stack buffer overflow conditions. The specific implementation targets the Firefox browser's JavaScript engine and memory management subsystems, making it particularly dangerous as it operates within the trusted execution environment of the web browser. The combination of JIT-spray and heap spray techniques creates a sophisticated attack pattern that can be used to bypass multiple layers of modern exploit mitigations.
Organizations affected by this vulnerability should immediately implement security updates to Firefox and Thunderbird versions that contain patches for this specific memory management flaw. The recommended mitigation strategy includes deploying the latest browser versions that contain fixes for the JavaScript engine's handling of asm.js code and memory allocation patterns. System administrators should also consider implementing additional browser hardening measures such as disabling asm.js functionality in environments where it is not required, and monitoring for unusual JavaScript execution patterns that might indicate exploitation attempts. The vulnerability's impact extends to any system running affected versions of Firefox or Thunderbird, making comprehensive patch management essential for maintaining security posture against this sophisticated attack vector.