CVE-2011-3426 in iOS
Summary
by MITRE
Cross-site scripting (XSS) vulnerability in Safari in Apple iOS before 5 allows remote web servers to inject arbitrary web script or HTML via a file accompanied by a "Content-Disposition: attachment" HTTP header.
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Analysis
by VulDB Data Team • 11/24/2021
The vulnerability identified as CVE-2011-3426 represents a significant cross-site scripting flaw affecting Apple iOS Safari browsers prior to version 5. This security weakness stems from the browser's improper handling of HTTP headers, specifically the Content-Disposition header with attachment directive, which creates an avenue for malicious web servers to execute arbitrary code within the context of the user's browsing session. The flaw operates by exploiting the browser's interpretation of file download headers, where attackers can manipulate the Content-Disposition header to trick Safari into executing malicious scripts during file handling operations.
The technical mechanism behind this vulnerability involves the interaction between HTTP headers and browser security policies. When Safari encounters a file with Content-Disposition: attachment, it typically prompts users to download the file rather than display it inline. However, the flaw occurs in how the browser processes certain combinations of headers and file types, allowing malicious content to bypass normal security restrictions. This particular implementation error creates a path where server-side attackers can inject script code that executes when users interact with the downloaded file, effectively exploiting the browser's file handling mechanisms.
The operational impact of this vulnerability extends beyond simple script injection, as it enables attackers to perform various malicious activities including session hijacking, credential theft, and redirection to malicious websites. The vulnerability affects users of iOS versions prior to 5, which at the time represented a substantial user base given Apple's market position. Attackers could leverage this weakness through compromised websites, malicious file downloads, or by exploiting web applications that do not properly validate or sanitize user-supplied content. The attack requires minimal user interaction, typically involving a simple download or navigation to a malicious website, making it particularly dangerous in real-world scenarios.
This vulnerability aligns with CWE-79, which specifically addresses cross-site scripting flaws in web applications, and demonstrates how improper input validation can lead to security breaches. The attack pattern follows the typical methodology outlined in the ATT&CK framework under T1059.001 for command and scripting interpreter, where attackers use browser-based scripting to execute malicious code. Organizations and users affected by this vulnerability should implement immediate mitigations including updating to iOS 5 or later, implementing proper web application firewalls, and conducting security awareness training to recognize potentially malicious downloads. Additionally, administrators should review and update Content-Disposition header handling in web applications, ensuring that servers properly sanitize headers and implement appropriate security measures to prevent script injection attacks. The vulnerability underscores the importance of maintaining up-to-date browser versions and implementing comprehensive security controls that address both client-side and server-side vulnerabilities in web environments.