CVE-2017-5376 in Firefox
Summary
by MITRE
Use-after-free while manipulating XSL in XSLT documents. This vulnerability affects Thunderbird < 45.7, Firefox ESR < 45.7, and Firefox < 51.
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Analysis
by VulDB Data Team • 11/26/2025
The vulnerability identified as CVE-2017-5376 represents a critical use-after-free flaw that occurs during the processing of XSLT documents within Mozilla's browser and email client applications. This issue manifests when the software handles XSL (Extensible Stylesheet Language) transformations, specifically during the manipulation of XSLT documents that contain maliciously crafted content. The vulnerability affects multiple Mozilla products including Thunderbird versions prior to 45.7, Firefox Extended Support Release versions before 45.7, and Firefox versions before 51. The flaw stems from improper memory management during XSLT processing operations, creating opportunities for attackers to exploit the software's handling of freed memory locations.
The technical implementation of this vulnerability involves a classic use-after-free condition that occurs when the application attempts to access memory that has already been deallocated during XSLT document processing. When parsing and executing XSLT transformations, the software allocates memory for temporary objects and structures used in the transformation process. However, under certain conditions involving malformed or malicious XSLT content, the application fails to properly manage the lifecycle of these memory allocations. This improper memory management allows an attacker to manipulate the XSLT document in such a way that when the software attempts to access previously freed memory locations, it can execute arbitrary code or cause unexpected behavior. The vulnerability is particularly dangerous because it can be triggered through web content or email attachments that contain crafted XSLT elements, making it exploitable through common attack vectors.
The operational impact of CVE-2017-5376 extends beyond simple memory corruption, as it provides attackers with potential pathways for remote code execution and system compromise. This vulnerability aligns with CWE-416, which specifically addresses use-after-free conditions in software implementations, and represents a significant risk to users who encounter malicious XSLT content in web browsers or email clients. The attack surface is broad given that the affected applications process XSLT content from various sources including web pages, email attachments, and potentially embedded content within documents. Successful exploitation could enable attackers to execute arbitrary code with the privileges of the affected application, potentially leading to complete system compromise, data exfiltration, or further lateral movement within a network environment. The vulnerability's impact is particularly severe in enterprise environments where email security and web browsing are common activities, as these are typical attack vectors for such exploits.
Mitigation strategies for CVE-2017-5376 primarily focus on immediate patching of affected software versions, with organizations urged to upgrade to Mozilla Firefox 51 or later, Firefox ESR 45.7 or later, and Thunderbird 45.7 or later. Security administrators should implement network-based protections including web filtering solutions that can block or sanitize XSLT content, particularly when it originates from untrusted sources. The implementation of Content Security Policy headers can help prevent the execution of malicious XSLT content within web applications, while email security solutions should include XSLT content scanning capabilities. Additionally, users should be educated about the risks of opening email attachments from unknown senders and visiting untrusted websites. The vulnerability demonstrates the importance of memory safety in modern software development practices, particularly for applications that process complex document formats and transformations. Organizations should also consider implementing sandboxing mechanisms and privilege separation techniques to limit the potential impact of successful exploits, aligning with defense-in-depth strategies recommended by cybersecurity frameworks such as those outlined in the MITRE ATT&CK framework for browser-based attacks.