CVE-2015-3751 in Safari
Summary
by MITRE
WebKit in Apple Safari before 6.2.8, 7.x before 7.1.8, and 8.x before 8.0.8, as used in iOS before 8.4.1 and other products, allows remote attackers to bypass a Content Security Policy protection mechanism by using a video control in conjunction with an IMG element within an OBJECT element.
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Analysis
by VulDB Data Team • 06/09/2022
The vulnerability identified as CVE-2015-3751 represents a critical bypass of Content Security Policy (CSP) protections within Apple Safari web browser implementations. This flaw affects multiple versions of Safari including those prior to 6.2.8, 7.1.8, and 8.0.8 across various iOS releases, specifically impacting iOS versions before 8.4.1. The vulnerability resides in the WebKit rendering engine component that powers Safari's web content processing capabilities, creating a significant security gap that undermines the intended protection mechanisms.
The technical exploitation mechanism involves a sophisticated manipulation of HTML element nesting and control structures. Attackers can circumvent CSP restrictions by strategically placing a video control element in conjunction with an IMG element nested within an OBJECT element. This specific combination exploits a parsing or rendering inconsistency in WebKit's handling of nested HTML elements, allowing malicious content to bypass the security policies that should normally prevent unauthorized resource loading. The vulnerability demonstrates a fundamental flaw in how the browser engine processes and validates nested element structures, particularly when dealing with multimedia content controls and embedded objects.
The operational impact of this vulnerability extends beyond simple content bypass, potentially enabling attackers to execute cross-site scripting attacks, load malicious resources, or harvest sensitive user data. When CSP is properly implemented, it should prevent unauthorized script execution and resource loading from untrusted domains. However, this bypass allows attackers to circumvent these protections by leveraging the specific HTML structure that triggers the rendering engine's inconsistent behavior. The vulnerability affects web applications that rely on CSP as a primary defense mechanism, potentially exposing users to various attack vectors including data exfiltration, credential theft, and session hijacking.
Security professionals should note this vulnerability's alignment with CWE-1021, which addresses improper restriction of XML external entity reference, and its relationship to ATT&CK technique T1211 for exploitation of web applications through browser-based attacks. The flaw represents a classic case of improper input validation within the browser's rendering engine, where the expected behavior of nested HTML elements does not properly enforce security boundaries. Organizations should implement immediate mitigation strategies including browser updates, enhanced monitoring for suspicious HTML content patterns, and additional security layers beyond CSP implementation. The vulnerability underscores the importance of comprehensive security testing for web rendering engines and highlights the critical need for continuous security assessments of browser components that handle complex HTML structures and multimedia content integration.