CVE-2015-0817 in Firefox
Summary
by MITRE
The asm.js implementation in Mozilla Firefox before 36.0.3, Firefox ESR 31.x before 31.5.2, and SeaMonkey before 2.33.1 does not properly determine the cases in which bounds checking may be safely skipped during JIT compilation and heap access, which allows remote attackers to read or write to unintended memory locations, and consequently execute arbitrary code, via crafted JavaScript.
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Analysis
by VulDB Data Team • 10/22/2024
The vulnerability identified as CVE-2015-0817 represents a critical security flaw in the asm.js implementation within Mozilla Firefox and SeaMonkey browsers. This issue affects versions prior to Firefox 36.0.3, Firefox ESR 31.x before 31.5.2, and SeaMonkey before 2.33.1, highlighting a fundamental weakness in the Just-In-Time compilation process that governs how JavaScript code is executed. The flaw specifically targets the optimization mechanisms that attempt to skip bounds checking during JIT compilation, a performance enhancement technique that should only be applied under strict conditions where memory safety can be guaranteed. When these conditions are improperly evaluated, the browser's security model becomes compromised, creating a pathway for attackers to exploit memory access patterns.
The technical root cause of this vulnerability lies in the improper determination of when bounds checking can be safely omitted during the JIT compilation phase of asm.js code execution. Asm.js is a low-level bytecode format designed to enable high-performance web applications by providing a subset of JavaScript that can be compiled to native machine code with minimal overhead. The vulnerability occurs because the JIT compiler fails to correctly assess the safety of skipping bounds checks in certain code paths, particularly when dealing with complex memory access patterns that involve dynamic indexing or indirect memory operations. This flaw creates a scenario where the compiler incorrectly assumes that memory operations are safe when they are not, leading to potential memory corruption. The vulnerability maps to CWE-129, which describes improper validation of array indices, and specifically relates to the improper handling of memory access boundaries during code optimization. According to ATT&CK framework, this vulnerability corresponds to T1059.007 for JavaScript and T1555.001 for credentials from password storage modules, as it enables arbitrary code execution through memory manipulation.
The operational impact of this vulnerability is severe and far-reaching, as it allows remote attackers to achieve arbitrary code execution on vulnerable systems through carefully crafted JavaScript payloads. Attackers can leverage this flaw to read or write to unintended memory locations, effectively bypassing the browser's memory protection mechanisms and executing malicious code with the privileges of the browser process. This capability enables a wide range of attack scenarios including but not limited to privilege escalation, data exfiltration, and system compromise. The vulnerability is particularly dangerous because it operates at the JIT compilation layer, meaning that even seemingly benign JavaScript code could contain malicious patterns that trigger the flaw during optimization. The memory corruption that results from this vulnerability can lead to unpredictable behavior, application crashes, or complete system compromise, depending on the specific memory locations that are accessed. Organizations using affected browser versions face significant risk as attackers can exploit this vulnerability through web-based attacks without requiring user interaction beyond visiting a malicious website, making it particularly insidious in modern web environments where users frequently encounter untrusted content. The vulnerability demonstrates the critical importance of proper bounds checking in JIT compilation systems and highlights the risks associated with aggressive optimization techniques that may compromise security guarantees.