CVE-2017-7808 in Firefox
Summary
by MITRE
A content security policy (CSP) "frame-ancestors" directive containing origins with paths allows for comparisons against those paths instead of the origin. This results in a cross-origin information leak of this path information. This vulnerability affects Firefox < 55.
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Analysis
by VulDB Data Team • 01/09/2021
The vulnerability described in CVE-2017-7808 represents a critical flaw in Firefox's implementation of Content Security Policy (CSP) frame-ancestors directive handling. This security weakness stems from improper parsing and comparison logic within the browser's CSP enforcement mechanism, specifically when dealing with origins that contain path components. The vulnerability affects Firefox versions prior to 55, indicating a long-standing issue that required significant development effort to resolve properly.
The technical flaw manifests when a web application implements a CSP policy with a frame-ancestors directive that includes origins containing paths, such as "https://example.com/path". Under normal circumstances, the frame-ancestors directive should enforce that a page can only be embedded within frames from specified origins. However, Firefox's implementation incorrectly compares the entire origin-path string against the actual origin of the embedding page, rather than just the origin component. This misimplementation allows attackers to infer path information from the embedding context, creating an information disclosure channel that violates fundamental security principles.
This cross-origin information leak occurs because the browser's CSP enforcement mechanism fails to properly normalize the origin components when performing comparisons. When an attacker crafts a malicious page with a CSP policy that includes path-based origins, they can potentially determine the path structure of the embedding page through the CSP violation reporting mechanism. The vulnerability essentially allows for a form of side-channel information disclosure where path information that should remain confidential becomes accessible to unauthorized parties.
The operational impact of this vulnerability extends beyond simple information disclosure, as it enables sophisticated attack scenarios that can be combined with other techniques to compromise user privacy and application security. Attackers could potentially map out application structures, identify sensitive endpoints, or gather intelligence about internal directory layouts through repeated CSP violation attempts. This vulnerability aligns with CWE-200, which describes improper handling of information exposure, and represents a clear violation of the principle of least privilege in web security.
The mitigation strategy for CVE-2017-7808 required Firefox developers to implement proper origin normalization within the CSP frame-ancestors directive processing. This involved ensuring that when comparing origins, the browser correctly isolates the origin component from any path information and performs comparisons only against the actual origin rather than the full origin-path string. The fix likely involved modifying the CSP enforcement engine to properly parse and normalize URLs before performing comparison operations, aligning with best practices for secure web application development and the ATT&CK framework's approach to mitigating information disclosure vulnerabilities. Organizations should ensure their Firefox installations are updated to version 55 or later to prevent exploitation of this vulnerability and maintain proper CSP enforcement behavior.