CVE-2016-2837 in Firefox
Summary
by MITRE
Heap-based buffer overflow in the ClearKey Content Decryption Module (CDM) in the Encrypted Media Extensions (EME) API in Mozilla Firefox before 48.0 and Firefox ESR 45.x before 45.3 might allow remote attackers to execute arbitrary code by providing a malformed video and leveraging a Gecko Media Plugin (GMP) sandbox bypass.
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Analysis
by VulDB Data Team • 10/23/2024
The vulnerability identified as CVE-2016-2837 represents a critical heap-based buffer overflow within Mozilla Firefox's implementation of the ClearKey Content Decryption Module as part of the Encrypted Media Extensions API. This flaw exists in Firefox versions prior to 48.0 and Firefox ESR 45.x versions prior to 45.3, specifically affecting the handling of encrypted media content through the Gecko Media Plugin framework. The vulnerability arises from insufficient input validation when processing malformed video content, creating a condition where attacker-controlled data can overwrite adjacent memory locations in the heap allocation space. The technical implementation involves the ClearKey CDM component which is responsible for decrypting protected media content, and it fails to properly bounds-check data received from media streams during the decryption process. This particular implementation flaw demonstrates a classic buffer overflow pattern where the application writes beyond the allocated buffer boundaries, potentially corrupting adjacent memory structures and enabling arbitrary code execution.
The operational impact of this vulnerability extends beyond simple code execution to encompass a sophisticated attack vector that leverages multiple layers of Firefox's media processing architecture. Attackers can craft specially malformed video content that, when processed by the affected ClearKey CDM, triggers the heap overflow condition. The vulnerability's exploitation becomes more dangerous due to its potential to bypass the Gecko Media Plugin sandbox, which is designed to isolate media processing components from the main browser environment. This sandbox bypass capability significantly increases the attack surface as it allows malicious code to escape the restricted plugin environment and potentially gain access to the broader browser process. The attack chain typically involves delivering malicious media content through web pages or other delivery mechanisms, where the victim's browser automatically attempts to process the content using the vulnerable ClearKey CDM, leading to memory corruption and potential remote code execution. The vulnerability aligns with CWE-121 Heap-based Buffer Overflow, which specifically addresses buffer overflows occurring in heap memory regions where insufficient bounds checking allows data to overwrite adjacent memory locations.
From a threat modeling perspective, this vulnerability presents significant risk to users of affected Firefox versions as it enables remote code execution without requiring user interaction beyond visiting a malicious website. The attack requires minimal user engagement since the exploitation occurs automatically during media playback, making it particularly dangerous in phishing scenarios or compromised websites. The vulnerability's classification under ATT&CK technique T1059.007 (Command and Scripting Interpreter: PowerShell) is relevant as the executed code could potentially leverage PowerShell or similar scripting capabilities. Security researchers have noted that the sandbox bypass component of this vulnerability makes it particularly concerning for enterprise environments where users may be browsing untrusted content. The exploitation of this vulnerability typically requires a sophisticated attacker with knowledge of memory corruption techniques and the ability to craft precise payloads that can successfully exploit the heap layout and bypass modern exploit mitigation techniques such as stack canaries or address space layout randomization. Organizations using affected Firefox versions face potential compromise of user systems, data theft, and further lateral movement within network environments.
The recommended mitigations for CVE-2016-2837 primarily focus on immediate version upgrades to Firefox 48.0 or Firefox ESR 45.3 and later releases where the vulnerability has been patched. Mozilla's patch addresses the buffer overflow condition by implementing proper bounds checking and input validation within the ClearKey CDM implementation, preventing the heap corruption that previously enabled arbitrary code execution. Additionally, organizations should consider implementing network-level protections such as content filtering and web application firewalls to prevent access to known malicious domains. Browser hardening measures including disabling unnecessary media plugins, restricting media playback capabilities, and implementing strict content security policies can further reduce the attack surface. The vulnerability highlights the importance of keeping media processing components updated as these systems often contain complex code paths that can introduce subtle security flaws. Regular security assessments of browser configurations and monitoring for exploitation attempts should be implemented as part of comprehensive security operations. Organizations should also consider deploying endpoint protection solutions that can detect and block suspicious memory access patterns or exploit attempts targeting similar buffer overflow vulnerabilities. The incident underscores the necessity of maintaining up-to-date security patches and the importance of vulnerability management programs that can quickly identify and remediate such critical flaws in browser-based media processing components.