CVE-2019-11725 in Firefox
Summary
by MITRE
When a user navigates to site marked as unsafe by the Safebrowsing API, warning messages are displayed and navigation is interrupted but resources from the same site loaded through websockets are not blocked, leading to the loading of unsafe resources and bypassing safebrowsing protections. This vulnerability affects Firefox < 68.
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Analysis
by VulDB Data Team • 07/10/2020
This vulnerability represents a critical bypass in Firefox's Safebrowsing protection mechanism that undermines the intended security posture when users encounter malicious websites. The flaw exists in the browser's handling of websockets connections during Safebrowsing warnings, creating a window of opportunity for attackers to load malicious resources despite the browser's protective measures. When Firefox encounters a site flagged as unsafe by the Safebrowsing API, it properly displays warning messages and interrupts navigation to the malicious site, yet fails to block websocket connections that may be established from the same domain. This inconsistency in protection allows attackers to maintain persistent communication channels with their servers while users are warned about the site's danger, effectively circumventing the intended security controls.
The technical implementation of this vulnerability stems from Firefox's inconsistent handling of different types of network connections during Safebrowsing enforcement. While the browser properly blocks traditional HTTP/HTTPS navigation requests to malicious sites, websocket connections are not subject to the same restrictions. This creates a scenario where the user interface properly warns about the unsafe site, but the underlying network infrastructure continues to allow connections that can be used to load additional malicious content, download payloads, or establish command and control channels. The flaw specifically affects Firefox versions prior to 68, indicating that this was a known issue in the browser's security architecture that was subsequently addressed in the update cycle.
From an operational perspective, this vulnerability enables sophisticated attack vectors that can bypass traditional browser security controls and maintain persistence on compromised systems. Attackers can leverage this bypass to establish covert communication channels with their command and control servers, download additional malware components, or exfiltrate data while users believe they are protected by Safebrowsing warnings. The vulnerability essentially creates a false sense of security where users are warned about dangerous sites but remain vulnerable to continued exploitation through websocket connections that are not properly filtered or blocked. This represents a significant concern for enterprise security as it demonstrates how incomplete security implementations can provide attackers with multiple pathways to compromise systems.
The vulnerability aligns with CWE-693, which addresses protection mechanism failures, specifically in the context of incomplete protection where security controls are bypassed through implementation gaps. From an ATT&CK framework perspective, this vulnerability maps to techniques involving defense evasion and persistence mechanisms, as attackers can maintain access through websocket connections while appearing to respect user warnings. The flaw also relates to TTPs involving initial access and execution, as the bypass allows for continued exploitation of compromised sessions. Organizations should implement immediate mitigations including Firefox updates to version 68 or later, network monitoring for suspicious websocket activity, and enhanced endpoint detection capabilities to identify unusual connections to known malicious domains. Additionally, security teams should conduct comprehensive assessments of their browser security policies and consider implementing additional network controls to block websocket connections to suspicious domains as a defensive measure against similar implementation gaps in security controls.