CVE-2017-5455 in Firefox
Summary
by MITRE
The internal feed reader APIs that crossed the sandbox barrier allowed for a sandbox escape and escalation of privilege if combined with another vulnerability that resulted in remote code execution inside the sandboxed process. This vulnerability affects Firefox ESR < 52.1 and Firefox < 53.
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Analysis
by VulDB Data Team • 11/26/2025
The vulnerability identified as CVE-2017-5455 represents a critical sandbox escape flaw in Mozilla Firefox browsers that fundamentally undermines the security model designed to protect users from malicious content. This issue specifically targets the internal feed reader APIs within Firefox's architecture, which were inadvertently exposed to cross-sandbox communication channels. The vulnerability stems from improper isolation mechanisms that allowed unauthorized access to privileged system resources from within the restricted sandbox environment where web content typically executes. When combined with other vulnerabilities that enable remote code execution within the sandboxed process, attackers could leverage this flaw to achieve complete system compromise and privilege escalation. The affected versions include Firefox Extended Support Release versions prior to 52.1 and standard Firefox versions prior to 53.0, representing a significant portion of the browser user base that was potentially exposed to this attack vector.
The technical implementation of this vulnerability exploits the fundamental principle of sandboxing by creating a pathway for unauthorized data flow between the restricted execution environment and the underlying operating system. The feed reader APIs, which are designed to process RSS and Atom feeds, contained logic that failed to properly enforce sandbox boundaries, allowing malicious code to access system resources that should have remained isolated. This flaw directly relates to CWE-276, which addresses improper privileges and access control issues, and more specifically to CWE-250, which deals with execution with unnecessary privileges. The vulnerability demonstrates how seemingly benign features can become attack vectors when proper security boundaries are not maintained. From an operational perspective, this issue represents a sophisticated attack surface that requires attackers to chain multiple vulnerabilities together, but the combination creates a highly effective exploitation pathway that bypasses traditional browser security mechanisms.
The operational impact of CVE-2017-5455 extends far beyond simple privilege escalation, as it provides attackers with the capability to execute arbitrary code with elevated system privileges. This vulnerability enables attackers to bypass the standard security model that protects users from malicious websites and content, potentially allowing for complete system compromise, data exfiltration, and persistent access to target machines. The attack requires a specific combination of conditions, including an initial foothold within the sandboxed environment through another vulnerability, but once achieved, the sandbox escape provides attackers with unprecedented access to system resources. This vulnerability aligns with ATT&CK technique T1059, which covers command and scripting interpreter, and T1068, which addresses exploit for privilege escalation. Organizations using affected versions of Firefox faced significant risk, as this vulnerability could be exploited through malicious web content without user interaction, making it particularly dangerous in enterprise environments where users frequently access untrusted web content. The exploitation of this vulnerability would typically occur through a multi-stage attack process where the initial compromise occurs through a different vulnerability, followed by the sandbox escape to gain elevated privileges.
Mitigation strategies for CVE-2017-5455 focus primarily on immediate version updates to patched Firefox releases, which address the underlying sandbox boundary violations in the feed reader APIs. System administrators should prioritize updating all affected Firefox installations to versions 52.1 or 53.0 and later, as these releases contain the necessary security fixes that properly enforce sandbox boundaries. Additional defensive measures include implementing network-based protections such as web application firewalls that can detect and block malicious feed content, as well as regular security assessments to identify potential exploitation attempts. The vulnerability highlights the importance of maintaining up-to-date browser security patches and demonstrates how even minor security flaws in specialized APIs can create significant attack vectors. Organizations should also consider implementing browser hardening measures, including disabling unnecessary features like feed readers in environments where they are not required, and monitoring for suspicious network activity that might indicate exploitation attempts. This vulnerability serves as a reminder of the critical importance of maintaining robust sandboxing mechanisms and proper access control enforcement in browser security architectures.