CVE-2020-12424 in Firefox
Summary
by MITRE
When constructing a permission prompt for WebRTC, a URI was supplied from the content process. This URI was untrusted, and could have been the URI of an origin that was previously granted permission; bypassing the prompt. This vulnerability affects Firefox < 78.
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Analysis
by VulDB Data Team • 07/10/2020
The vulnerability identified as CVE-2020-12424 represents a critical permission bypass flaw in the Firefox web browser's implementation of WebRTC functionality. This issue stems from improper handling of URI validation during the construction of permission prompts, creating a scenario where malicious actors could exploit the browser's trust model to circumvent security mechanisms designed to protect users from unauthorized access to device resources. The vulnerability specifically affects Firefox versions prior to 78, indicating a window of exposure where users were susceptible to attacks targeting the browser's WebRTC permission system.
The technical root cause of this vulnerability lies in the improper validation of URIs within the content process when generating WebRTC permission prompts. During the WebRTC permission flow, Firefox constructs a prompt to notify users when web applications request access to device resources such as cameras, microphones, or other media devices. However, the browser failed to properly sanitize or validate the URI supplied from the content process, which could contain untrusted data from previously granted permissions. This flaw allowed attackers to manipulate the URI to reference origins that had already been granted permissions, effectively bypassing the permission prompt mechanism and enabling unauthorized access to device resources without user consent.
The operational impact of this vulnerability extends beyond simple permission bypass, as it fundamentally undermines the security model that protects users from unauthorized access to their device hardware. When an attacker successfully exploits this vulnerability, they can gain access to sensitive device resources without user awareness or consent, potentially leading to surveillance, data exfiltration, or other malicious activities. The attack vector typically involves constructing a malicious WebRTC request that leverages the URI manipulation to reference trusted origins, thereby circumventing the normal permission flow that should require explicit user interaction. This vulnerability directly impacts the principle of least privilege and user consent that forms the foundation of modern browser security architectures.
This vulnerability maps to CWE-20: Improper Input Validation, specifically relating to insufficient validation of input data from untrusted sources. The flaw demonstrates a classic case of trust boundary violation where the browser's permission system fails to properly validate data integrity between different security contexts. From an ATT&CK perspective, this vulnerability aligns with techniques such as T1059.001 (Command and Scripting Interpreter: PowerShell) and T1071.004 (Application Layer Protocol: DNS) when attackers leverage the bypassed permissions to establish persistent access or exfiltrate data. The vulnerability also relates to T1566 (Phishing) as attackers could craft convincing WebRTC prompts that appear legitimate while exploiting this bypass mechanism to gain unauthorized access.
Mitigation strategies for this vulnerability involve immediate deployment of Firefox version 78 or later, which contains the necessary patches to address the URI validation flaw in the WebRTC permission system. Organizations should also implement browser hardening measures including disabling unnecessary WebRTC functionality where possible, monitoring for suspicious permission requests, and maintaining up-to-date security policies. Security teams should conduct regular audits of browser configurations and ensure that users are educated about the importance of permission prompts and the risks associated with granting access to device resources. Additionally, network-level monitoring can help detect anomalous WebRTC traffic patterns that might indicate exploitation attempts, while endpoint detection and response solutions can provide visibility into potential abuse of the bypassed permission mechanism.