CVE-2019-8771 in iOS
Summary
by MITRE • 10/28/2020
This issue was addressed with improved iframe sandbox enforcement. This issue is fixed in Safari 13.0.1, iOS 13. Maliciously crafted web content may violate iframe sandboxing policy.
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Analysis
by VulDB Data Team • 11/28/2020
The vulnerability described in CVE-2019-8771 represents a critical sandboxing bypass in Apple's Safari browser that could allow malicious web content to circumvent security restrictions imposed on iframe elements. This flaw specifically targeted the iframe sandbox enforcement mechanisms that are fundamental to web browser security architectures, creating a potential pathway for attackers to execute unauthorized actions within the context of sandboxed content. The issue was particularly concerning because iframe sandboxing serves as a crucial security boundary that prevents embedded content from accessing parent page resources, executing scripts, or navigating the top-level browsing context.
The technical implementation of this vulnerability involved sophisticated manipulation of iframe sandbox attributes and their associated security policies, allowing malicious actors to bypass the intended restrictions that should isolate potentially harmful content from the main browsing context. This type of flaw falls under the category of sandbox escape vulnerabilities where attackers can undermine the isolation mechanisms that browsers implement to protect users from malicious web content. The vulnerability specifically affected Safari versions prior to 13.0.1 and iOS versions prior to 13, indicating that the security model had been compromised at the browser engine level where iframe sandboxing policies were not being properly enforced. This weakness could potentially enable attackers to perform actions such as accessing parent window objects, executing scripts outside the sandboxed context, or redirecting the top-level browsing context.
The operational impact of this vulnerability extends beyond simple privilege escalation, as it could enable attackers to perform more sophisticated attacks such as cross-site scripting, session hijacking, or information disclosure through the bypassed security boundaries. The flaw represents a direct violation of the security principle of least privilege that should apply to embedded content, allowing malicious actors to gain unauthorized access to resources that should remain protected. This vulnerability aligns with CWE-693, which describes protection mechanism failures, specifically those related to sandboxing and access control mechanisms. The exploitation of this vulnerability could enable attackers to leverage the browser's security model in ways that would normally be prevented, potentially leading to complete browser compromise or user data theft.
Mitigation strategies for this vulnerability required immediate browser updates to versions that implemented proper iframe sandbox enforcement. Organizations should have ensured that all users were upgraded to Safari 13.0.1 or later, and iOS 13 or later, where the security fixes were implemented. The fix likely involved strengthening the browser's iframe sandboxing implementation to properly validate and enforce sandbox attributes, ensuring that malicious content cannot bypass these security controls. Security teams should have conducted thorough testing of their web applications to verify that iframe sandboxing was functioning correctly and that no legacy content was relying on potentially insecure sandbox behaviors. This vulnerability demonstrates the critical importance of maintaining up-to-date browser security implementations and highlights the potential for sophisticated attacks that exploit fundamental browser security mechanisms. The remediation process would have required not only updating browser versions but also re-evaluating web application security practices that rely on iframe sandboxing for protection against malicious content.