CVE-2015-2712 in Firefox
Summary
by MITRE
The asm.js implementation in Mozilla Firefox before 38.0 does not properly determine heap lengths during identification of cases in which bounds checking may be safely skipped, which allows remote attackers to trigger out-of-bounds write operations and possibly execute arbitrary code, or trigger out-of-bounds read operations and possibly obtain sensitive information from process memory, via crafted JavaScript.
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Analysis
by VulDB Data Team • 05/17/2022
The vulnerability identified as CVE-2015-2712 represents a critical flaw in Mozilla Firefox's asm.js implementation that directly impacts the browser's security model and memory management capabilities. This issue affects versions prior to Firefox 38.0 and stems from improper heap length determination during the analysis phase of asm.js code execution. The asm.js specification is designed to provide high-performance JavaScript execution by enabling compilers to generate optimized machine code, but this particular implementation flaw creates a dangerous condition where the browser's bounds checking mechanisms can be bypassed under specific circumstances. The vulnerability operates at the intersection of JavaScript interpretation and low-level memory management, creating a pathway for attackers to manipulate memory access patterns that should normally be protected by the browser's security boundaries.
The technical nature of this vulnerability lies in the flawed algorithm used by Firefox to identify cases where bounds checking can be safely skipped during asm.js execution. When the browser's JIT compiler analyzes asm.js code, it attempts to optimize performance by eliminating redundant bounds checks that would normally occur during array access operations. However, the implementation contains a logic error that causes incorrect determination of heap boundaries, leading to situations where the compiler incorrectly concludes that bounds checking is unnecessary when it should remain active. This misidentification creates a condition where out-of-bounds memory operations can occur without proper protection, potentially allowing attackers to write data beyond allocated memory regions or read from memory locations that should be inaccessible. The flaw specifically affects the heap management system that handles memory allocation for asm.js arrays and other data structures, making it particularly dangerous in the context of web-based attacks.
The operational impact of CVE-2015-2712 extends beyond simple memory corruption to potentially enable full remote code execution capabilities. Attackers can leverage this vulnerability to perform out-of-bounds write operations that may overwrite critical memory structures, potentially leading to arbitrary code execution with the privileges of the browser process. Additionally, the vulnerability can be exploited for out-of-bounds read operations that allow information disclosure, enabling attackers to extract sensitive data from process memory including cookies, passwords, or other confidential information. This dual nature of the vulnerability makes it particularly dangerous as it can be used for both offensive and reconnaissance purposes. The attack vector requires the victim to visit a malicious website containing crafted JavaScript code, making it a typical web-based exploit that can be delivered through various means including phishing campaigns, malicious advertisements, or compromised websites. The vulnerability's exploitation is particularly concerning because asm.js is designed for high-performance applications and is increasingly used in modern web applications, making the attack surface larger than initially apparent.
This vulnerability aligns with CWE-129, which addresses improper validation of array indices, and represents a specific instance of improper bounds checking in a performance-optimized execution environment. From an ATT&CK perspective, this flaw maps to techniques involving code injection and memory corruption, specifically targeting the execution environment through JavaScript-based attacks. The vulnerability demonstrates the complexity that arises when implementing high-performance features in security-sensitive environments, where optimization efforts can inadvertently create security weaknesses. The fix implemented by Mozilla in Firefox 38.0 involved correcting the heap length determination logic and strengthening the bounds checking algorithms to prevent the incorrect optimization decisions that led to the vulnerability. Organizations should prioritize updating to patched versions of Firefox and other affected browsers, as the vulnerability can be exploited remotely without user interaction and provides attackers with significant capabilities for system compromise. The incident underscores the importance of thorough security testing for performance optimization features and the need for careful consideration of security implications in high-performance computing environments.