CVE-2017-5448 in Firefox
Summary
by MITRE
An out-of-bounds write in "ClearKeyDecryptor" while decrypting some Clearkey-encrypted media content. The "ClearKeyDecryptor" code runs within the Gecko Media Plugin (GMP) sandbox. If a second mechanism is found to escape the sandbox, this vulnerability allows for the writing of arbitrary data within memory, resulting in a potentially exploitable crash. This vulnerability affects Firefox ESR < 45.9, Firefox ESR < 52.1, and Firefox < 53.
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Analysis
by VulDB Data Team • 11/26/2025
The CVE-2017-5448 vulnerability represents a critical out-of-bounds write flaw within the ClearKeyDecryptor component of Firefox's Gecko Media Plugin architecture. This vulnerability specifically targets the handling of Clearkey-encrypted media content, which is a widely used DRM (Digital Rights Management) format for protecting multimedia content. The ClearKeyDecryptor operates within the Gecko Media Plugin sandbox environment, which is designed to isolate media processing functions from the main browser engine to prevent privilege escalation attacks. However, this particular vulnerability demonstrates how memory corruption flaws within sandboxed components can still pose significant security risks when combined with other exploitation vectors.
The technical nature of this vulnerability stems from improper bounds checking within the ClearKeyDecryptor's memory management routines during decryption operations. When processing certain Clearkey-encrypted media streams, the decryption routine fails to validate array indices or buffer boundaries, allowing an attacker to write data beyond the allocated memory space. This out-of-bounds write condition occurs in the GMP sandbox context, where the decryption process executes with restricted privileges but still maintains access to memory regions that could be manipulated. The vulnerability is particularly concerning because it operates within a trusted code path that handles sensitive media content, making it an attractive target for attackers seeking to exploit the browser's media processing capabilities.
The operational impact of CVE-2017-5448 extends beyond simple memory corruption, as it creates a potential pathway for privilege escalation when combined with a second exploitation mechanism. The vulnerability affects multiple Firefox versions including Firefox ESR 45.9 and earlier, Firefox ESR 52.1 and earlier, and Firefox 53 and earlier releases. This widespread impact across different browser versions indicates that the flaw was present in the media processing pipeline for an extended period. The sandbox escape scenario mentioned in the vulnerability description aligns with ATT&CK framework techniques such as T1068 (Local Privilege Escalation) and T1190 (Exploit Public-Facing Application), where an attacker could potentially leverage the memory corruption to execute arbitrary code with elevated privileges. The vulnerability's exploitation potential is further enhanced by the fact that media content delivery is a common attack surface, as demonstrated by various real-world exploitation techniques targeting browser media plugins.
Mitigation strategies for CVE-2017-5448 primarily focus on immediate version updates and browser hardening measures. Organizations should prioritize upgrading to Firefox versions that contain the patched ClearKeyDecryptor implementation, specifically Firefox 52.1 or later for ESR releases, and Firefox 53 or later for regular releases. The vulnerability's classification under CWE-787 (Out-of-bounds Write) indicates that proper input validation and bounds checking should be implemented throughout the media processing pipeline. Security researchers have noted that this vulnerability highlights the importance of robust sandboxing mechanisms and proper memory management in browser media plugins. Additional mitigations include implementing Content Security Policy directives to restrict media content sources, disabling unnecessary media features, and deploying network-level protections such as web application firewalls to monitor for exploitation attempts. The vulnerability also emphasizes the need for comprehensive security testing of media processing components, particularly those handling encrypted content, as outlined in industry standards for secure software development practices.