CVE-2020-15652 in Firefox
Summary
by MITRE
By observing the stack trace for JavaScript errors in web workers, it was possible to leak the result of a cross-origin redirect. This applied only to content that can be parsed as script. This vulnerability affects Firefox < 79, Firefox ESR < 68.11, Firefox ESR < 78.1, Thunderbird < 68.11, and Thunderbird < 78.1.
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Analysis
by VulDB Data Team • 08/11/2020
This vulnerability represents a cross-origin information disclosure flaw that exploits the handling of JavaScript error stack traces within web worker contexts. The security issue arises from the fact that when JavaScript errors occur in web workers, the stack trace information can inadvertently reveal details about cross-origin redirects that should normally be restricted by browser security policies. The flaw specifically impacts content that can be parsed as script, meaning that only resources that are interpreted as executable JavaScript code are susceptible to this information leakage. The vulnerability demonstrates a breakdown in the browser's security model where the error reporting mechanism becomes a vector for cross-origin data exposure, effectively bypassing the same-origin policy that normally prevents such information leakage between different origins.
The technical implementation of this vulnerability stems from how Firefox handles error reporting in web worker environments. When a web worker encounters a JavaScript error during execution, the browser generates a stack trace that includes information about the execution context. Under normal circumstances, this stack trace should not contain sensitive cross-origin redirect information, but due to the implementation flaw, the error context can reveal details about redirect operations that occurred across origin boundaries. This particular weakness affects the browser's security boundary enforcement, where the stack trace generation process fails to properly sanitize cross-origin information that might be embedded within the error context. The vulnerability is classified as a type of information disclosure that falls under the broader category of cross-origin resource access violations, which is a fundamental security concern in web browser architecture.
The operational impact of this vulnerability extends beyond simple information leakage, as it provides attackers with a method to gather cross-origin redirect information that could be used for further exploitation. An attacker could potentially construct a malicious web page that triggers specific error conditions in web workers, then analyze the resulting stack traces to reconstruct information about cross-origin redirects that occurred during the execution of legitimate web content. This type of information leakage could be particularly dangerous in environments where cross-origin redirects might reveal internal network structures, server configurations, or other sensitive information that should remain hidden from external parties. The vulnerability affects multiple browser products including Firefox, Firefox ESR, and Thunderbird, indicating a widespread implementation issue that impacts both desktop and email clients. The specific versions affected demonstrate that this was a long-standing issue that required patching across multiple product lines and release channels.
Mitigation strategies for this vulnerability involve implementing proper stack trace sanitization within web worker error handling mechanisms and ensuring that cross-origin information is properly filtered from error reporting contexts. Browser vendors should implement stricter controls over how error context information is exposed, particularly in environments where web workers execute code that might interact with cross-origin resources. The fix typically involves modifying the error reporting system to prevent cross-origin redirect information from being embedded in stack traces, which aligns with the principle of least privilege in security design. This vulnerability also highlights the importance of proper error handling and context management in web applications, particularly those that rely on web worker environments for processing. Security practitioners should monitor for updates to affected browser versions and ensure that systems are running patched versions that address this information disclosure vector. The remediation process should include verification that error reporting mechanisms properly sanitize cross-origin context information and that web applications are not inadvertently exposing sensitive information through error handling pathways. This vulnerability is categorized under CWE-200 (Information Exposure) and relates to ATT&CK techniques involving information gathering and reconnaissance activities that could be used to map network environments and identify potential attack vectors.