CVE-2017-5375 in Firefox
Summary
by MITRE
JIT code allocation can allow for a bypass of ASLR and DEP protections leading to potential memory corruption attacks. This vulnerability affects Thunderbird < 45.7, Firefox ESR < 45.7, and Firefox < 51.
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Analysis
by VulDB Data Team • 11/25/2025
The vulnerability described in CVE-2017-5375 represents a critical flaw in JavaScript Just-In-Time compilation mechanisms within Mozilla Firefox and Thunderbird browsers. This issue specifically targets the memory management systems that handle dynamic code generation during runtime execution. The vulnerability exploits weaknesses in how the JavaScript engine allocates memory for generated code, creating opportunities for attackers to circumvent fundamental security protections that are designed to prevent exploitation. The flaw exists in the interaction between the JIT compiler and memory allocation routines, where improper memory layout handling allows for predictable memory addresses that should otherwise be randomized by ASLR.
The technical implementation of this vulnerability stems from insufficient memory randomization during JIT code generation processes. When the JavaScript engine compiles code on-the-fly, it allocates memory regions for the generated machine code. In affected versions, these allocations do not properly randomize memory addresses, allowing attackers to predict or control where executable code will be placed in memory. This bypass of ASLR protection means that attackers can reliably target specific memory locations regardless of the operating system's address space layout randomization defenses. The vulnerability also impacts DEP (Data Execution Prevention) mechanisms, which typically prevent execution of code in data segments, by enabling attackers to place executable code in memory regions that would normally be protected.
The operational impact of this vulnerability extends beyond simple memory corruption, creating a pathway for sophisticated attack vectors that can bypass multiple layers of modern security defenses. Attackers can leverage this weakness to execute arbitrary code with the privileges of the browser process, potentially leading to complete system compromise. The vulnerability affects both Firefox ESR and regular Firefox releases, as well as Thunderbird email clients, indicating it's a fundamental issue within the underlying JavaScript engine rather than a product-specific flaw. This widespread impact means that organizations using any of these browsers or email clients are vulnerable to attacks that can bypass security controls designed to prevent such exploitation. The vulnerability's exploitation requires careful crafting of JavaScript code that can trigger the specific memory allocation patterns, making it a sophisticated attack vector that requires advanced knowledge of the browser's internal workings.
Mitigation strategies for CVE-2017-5375 primarily focus on immediate software updates and patches provided by Mozilla. Organizations should prioritize updating all affected browsers and email clients to versions that include fixes for the JIT memory allocation issues. The vulnerability aligns with attack patterns described in the ATT&CK framework under code injection and privilege escalation techniques, where adversaries exploit memory management flaws to bypass security controls. Security teams should implement network monitoring to detect potential exploitation attempts targeting this vulnerability, particularly in environments where these browsers are in use. The fix typically involves implementing proper memory randomization during JIT code allocation and ensuring that generated code is placed in memory regions that maintain the expected security properties. Additionally, organizations should consider implementing additional security measures such as sandboxing, content security policies, and regular security assessments to reduce the overall attack surface and limit the potential impact of similar vulnerabilities in the future. This vulnerability demonstrates the ongoing challenges in securing modern web browsers where dynamic code generation creates complex security implications that can undermine fundamental protection mechanisms.