CVE-2018-5175 in Firefox
Summary
by MITRE
A mechanism to bypass Content Security Policy (CSP) protections on sites that have a "script-src" policy of "'strict-dynamic'". If a target website contains an HTML injection flaw an attacker could inject a reference to a copy of the "require.js" library that is part of Firefox's Developer Tools, and then use a known technique using that library to bypass the CSP restrictions on executing injected scripts. This vulnerability affects Firefox < 60.
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Analysis
by VulDB Data Team • 07/20/2024
The vulnerability described in CVE-2018-5175 represents a sophisticated bypass of Content Security Policy protections that specifically targets Firefox browsers version 60 and earlier. This weakness exploits a fundamental flaw in how Firefox handled certain script execution contexts when combined with the strict-dynamic directive of CSP policies. The vulnerability operates through a multi-stage attack vector that leverages HTML injection flaws present in target websites to manipulate the browser's security mechanisms. The attack specifically targets sites that implement CSP with script-src 'strict-dynamic' which should theoretically prevent unauthorized script execution by allowing only scripts that can be validated through a strict dynamic policy. However, this bypass demonstrates that certain conditions can be manipulated to circumvent these protections through the use of legitimate libraries that are part of Firefox's developer tools ecosystem.
The technical exploitation mechanism relies on the attacker's ability to inject HTML content into vulnerable web applications, specifically targeting the inclusion of a copy of the require.js library that is bundled with Firefox's Developer Tools. This particular library serves as a stepping stone because it contains functionality that can be leveraged to manipulate script execution contexts within the browser. The bypass technique utilizes known patterns of how require.js can be manipulated to execute scripts in ways that circumvent the CSP restrictions, effectively allowing attackers to inject and execute malicious JavaScript code that would normally be blocked by the security policy. The vulnerability essentially creates a trusted execution context that can be used to bypass the intended security boundaries established by the CSP implementation. This represents a significant weakness in Firefox's security model as it demonstrates how legitimate development tools can be weaponized to undermine security policies that are designed to protect users from cross-site scripting attacks.
The operational impact of this vulnerability is substantial as it affects the core security mechanism that web applications rely upon to protect against script injection attacks. When successful, this bypass allows attackers to execute arbitrary JavaScript code in the context of the target website, potentially leading to session hijacking, data exfiltration, or further exploitation of the user's browsing session. The vulnerability is particularly concerning because it affects a widely used browser and can be exploited through common injection flaws that exist in many web applications. The attack requires only that the target website contains an HTML injection vulnerability, which is relatively common in web applications, making this bypass a significant threat to web security. The fact that this vulnerability affects Firefox versions prior to 60 means that a substantial portion of users who had not updated their browsers remained vulnerable to this specific attack vector that could be used to circumvent security controls that were specifically designed to prevent such attacks.
The exploitation of this vulnerability aligns with several ATT&CK framework techniques including T1059.007 for scripting and T1211 for exploitation for defense evasion, demonstrating how attackers can leverage legitimate browser components to bypass security controls. From a CWE perspective, this vulnerability relates to CWE-15 (External Control of System or Configuration Setting) and CWE-94 (Improper Control of Generation of Code) as it involves manipulation of script execution contexts through external components. The vulnerability also highlights issues with CWE-352 (Cross-Site Request Forgery) and CWE-79 (Cross-Site Scripting) as it combines injection flaws with bypass techniques to undermine security policies. Organizations should implement comprehensive browser security policies and ensure timely updates to address this vulnerability, as well as conduct regular security assessments to identify and remediate HTML injection flaws that could be exploited in similar ways. The fix for this vulnerability required modifications to Firefox's CSP implementation to properly handle script execution contexts when legitimate libraries are present, demonstrating the complexity of modern browser security mechanisms and the need for continuous security improvements in web applications and browsers alike.