CVE-2017-7755 in Firefox
Summary
by MITRE
The Firefox installer on Windows can be made to load malicious DLL files stored in the same directory as the installer when it is run. This allows privileged execution if the installer is run with elevated privileges. Note: This attack only affects Windows operating systems. Other operating systems are unaffected. This vulnerability affects Firefox < 54, Firefox ESR < 52.2, and Thunderbird < 52.2.
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Analysis
by VulDB Data Team • 11/26/2025
The vulnerability identified as CVE-2017-7755 represents a critical privilege escalation flaw within the Firefox installer for Windows operating systems. This security weakness stems from improper handling of dynamic link library loading mechanisms during the installation process, creating an avenue for malicious code execution. The vulnerability specifically targets the Windows installer executable which fails to properly validate or restrict the loading of external DLL files from the same directory, allowing attackers to place malicious components alongside the legitimate installer. This design flaw directly violates secure coding principles and establishes a dangerous attack vector that can be exploited by adversaries with minimal technical expertise.
The technical implementation of this vulnerability exploits the Windows DLL search order mechanism, where the system loads DLL files from the current working directory before checking system directories. When an attacker places a malicious DLL with the same name as a legitimate dependency in the same folder as the Firefox installer, the system will load the malicious version instead of the legitimate one. This behavior creates a classic DLL hijacking scenario that aligns with CWE-426 and ATT&CK technique T1059.001, where adversaries leverage legitimate system tools to execute malicious code. The vulnerability is particularly dangerous because it requires no user interaction beyond running the installer, and the attack can succeed even when the installer is executed with elevated privileges, making it a high-impact privilege escalation vector.
The operational impact of CVE-2017-7755 extends beyond simple code execution to encompass full system compromise when the installer is run with administrative privileges. This vulnerability affects a broad range of Firefox versions including the main release line and extended support releases, creating widespread exposure across enterprise environments. Organizations that deploy Firefox through automated installation processes or allow users to run installers with elevated permissions face significant risk of unauthorized system access. The vulnerability's impact is amplified by the fact that it can be exploited in various attack scenarios including social engineering campaigns, where attackers convince users to run modified installers, or through supply chain compromises where legitimate installers are replaced with malicious versions. The attack requires no specialized knowledge of the target system beyond basic file manipulation capabilities, making it accessible to threat actors of varying skill levels.
Mitigation strategies for CVE-2017-7755 focus primarily on immediate version upgrades to patched releases of Firefox and Thunderbird, as the vulnerability was resolved through proper DLL loading mechanisms in subsequent releases. Organizations should implement strict access controls and privilege separation for installation processes, ensuring that installers are not executed with elevated privileges unless absolutely necessary. Network-level protections including application whitelisting and endpoint detection systems can help prevent the execution of unauthorized DLL files. System administrators should conduct thorough inventory checks to identify and remove any modified installer files from user directories or shared network locations. The vulnerability demonstrates the importance of secure installation practices and proper DLL loading procedures, reinforcing the need for defense-in-depth strategies that include both application-level hardening and operational security measures. Regular security assessments and vulnerability scanning should be implemented to identify potential instances of this vulnerability in legacy systems or custom deployment scenarios where automatic updates may not be feasible.