CVE-2018-5106 in Firefox
Summary
by MITRE
Style editor traffic in the Developer Tools can be routed through a service worker hosted on a third party website if a user selects error links when these tools are open. This can allow style editor information used within Developer Tools to leak cross-origin. This vulnerability affects Firefox < 58.
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Analysis
by VulDB Data Team • 02/01/2021
This vulnerability in Firefox versions prior to 58 represents a cross-origin information leakage issue that exploits the interaction between developer tools and service workers. The flaw occurs when users interact with error links while Developer Tools are open, allowing traffic from the style editor to be redirected through a service worker hosted on a third-party domain. This creates an unexpected pathway for sensitive styling information to be exposed beyond its intended origin boundaries, fundamentally compromising the browser's security model that relies on strict origin policies to isolate web content.
The technical implementation of this vulnerability stems from Firefox's handling of service worker routing within developer tool contexts. When a user clicks on error links in Developer Tools, the browser's internal mechanisms for managing style editor traffic become susceptible to manipulation through third-party service workers. This occurs because the developer tools interface does not properly enforce origin isolation when service workers are active, allowing cross-origin requests to be processed through the style editor subsystem. The vulnerability is particularly concerning because it operates at the intersection of browser debugging capabilities and web security boundaries, where the normal protective mechanisms fail to prevent unauthorized data flow.
The operational impact of this vulnerability extends beyond simple information disclosure to potentially enable more sophisticated attacks. An attacker who can inject a service worker on a third-party site could potentially harvest styling information from multiple origins that the user has visited while developer tools were open. This could reveal detailed information about web applications including CSS selectors, layout structures, and potentially even sensitive styling patterns that might be used in subsequent attacks. The vulnerability is particularly dangerous in environments where users frequently debug web applications or visit multiple sites with developer tools active, as it creates a persistent attack surface that can be exploited over time.
This issue aligns with CWE-200, which addresses "Information Exposure," and demonstrates how improper handling of cross-origin communication can lead to security vulnerabilities. The ATT&CK framework categorizes this under T1557, "Adversarial Infrastructure," as it leverages legitimate browser features to create unauthorized communication channels. The vulnerability also relates to T1071.004, "Application Layer Protocol: DNS," since it involves the manipulation of network traffic through service worker interception. Organizations should implement mitigations including keeping Firefox updated to version 58 or later, where the vulnerability has been patched, and establishing policies that discourage keeping developer tools open when visiting untrusted websites. Additionally, browser security configurations should be reviewed to ensure proper service worker isolation and origin enforcement mechanisms are active to prevent similar cross-origin leakage scenarios.