CVE-2017-5405 in Firefox
Summary
by MITRE
Certain response codes in FTP connections can result in the use of uninitialized values for ports in FTP operations. 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
This vulnerability resides in the File Transfer Protocol implementation within Mozilla Firefox and Thunderbird email clients, specifically impacting versions prior to 52 and 45.8 respectively. The issue manifests when processing certain FTP response codes that trigger the use of uninitialized memory values for port assignments during FTP operations. The flaw stems from improper handling of FTP server responses where the client fails to properly initialize port variables before utilizing them in subsequent network operations. This represents a classic uninitialized memory access vulnerability that can lead to unpredictable behavior and potential exploitation.
The technical implementation of this vulnerability involves the FTP protocol handler within the browser's network stack where response codes from FTP servers are parsed and processed. When specific response codes are received, the application attempts to extract port information from the server response but fails to properly initialize the memory locations that will store this port data. This uninitialized memory may contain arbitrary values from previous operations, leading to incorrect port assignments during FTP connection establishment. The vulnerability is particularly concerning because FTP operations are often used for downloading content, and malicious FTP servers could potentially craft responses that exploit this uninitialized value usage to redirect connections or execute arbitrary code.
The operational impact of this vulnerability extends beyond simple functionality issues to potential security breaches. Attackers could exploit this weakness by hosting malicious FTP servers that respond with crafted codes designed to trigger the uninitialized memory usage. This could lead to various attack vectors including man-in-the-middle scenarios where connections are redirected to attacker-controlled systems, or more severe exploitation techniques that leverage the uninitialized memory values to achieve code execution. The vulnerability affects not only web browsing but also email functionality since Thunderbird is impacted, making it a comprehensive issue across Mozilla's product suite. This aligns with CWE-457 which specifically addresses the use of uninitialized variables in software development practices.
Mitigation strategies for this vulnerability require immediate patching of affected software versions to ensure proper initialization of memory variables before FTP port operations. Organizations should prioritize updating Firefox and Thunderbird installations to versions 52 and 45.8 respectively, as these releases contain the necessary fixes for the uninitialized memory handling in FTP response processing. Network administrators should also implement monitoring for suspicious FTP traffic patterns that might indicate exploitation attempts, while security teams should consider implementing network segmentation to limit exposure of vulnerable systems. The ATT&CK framework categorizes this vulnerability under the T1071.004 technique for application layer protocol usage, specifically targeting FTP communications where the uninitialized memory vulnerability could be leveraged for lateral movement or data exfiltration. System administrators should also consider implementing web application firewalls that can detect and block suspicious FTP response patterns that might exploit this vulnerability.