CVE-2016-4651 in iOS
Summary
by MITRE
Cross-site scripting (XSS) vulnerability in the WebKit JavaScript bindings in Apple iOS before 9.3.3 and Safari before 9.1.2 allows remote attackers to inject arbitrary web script or HTML via a crafted HTTP/0.9 response, related to a "cross-protocol cross-site scripting (XPXSS)" vulnerability.
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Analysis
by VulDB Data Team • 09/05/2022
The CVE-2016-4651 vulnerability represents a critical cross-site scripting flaw that existed in Apple's WebKit JavaScript bindings across iOS versions prior to 9.3.3 and Safari versions before 9.1.2. This vulnerability falls under the broader category of cross-protocol cross-site scripting attacks, which exploit the interaction between different protocols to bypass traditional security measures. The flaw specifically leverages HTTP/0.9 responses to inject malicious scripts into web applications, making it particularly dangerous as it can be triggered through seemingly benign protocol interactions. The vulnerability demonstrates how protocol-level inconsistencies can create unexpected attack vectors that bypass conventional web security controls.
The technical implementation of this vulnerability stems from how WebKit handles HTTP/0.9 responses within its JavaScript binding mechanisms. HTTP/0.9 is the original version of the HTTP protocol that lacks headers and only supports GET requests with simple responses. When WebKit processes these responses, it fails to properly sanitize or validate the content, allowing attackers to craft malicious HTTP/0.9 responses that contain embedded JavaScript or HTML code. This occurs because the JavaScript bindings do not adequately distinguish between legitimate protocol responses and potentially malicious content, particularly when cross-protocol interactions occur between different HTTP versions or protocols. The flaw essentially creates a pathway where content intended for one protocol context can be interpreted as executable code in another protocol context.
The operational impact of this vulnerability is significant for users of affected Apple platforms, as it enables remote attackers to execute arbitrary web scripts or HTML code on vulnerable systems. Attackers can leverage this vulnerability to perform session hijacking, steal user credentials, deface websites, or redirect users to malicious sites. The cross-protocol nature of the attack means that traditional security measures such as content security policies or input validation may not effectively protect against this specific threat vector. Users of iOS 9.2.x and earlier versions, as well as Safari 9.1.1 and earlier, were particularly at risk since these versions did not include the necessary protections against malformed HTTP/0.9 responses. The vulnerability could be exploited through various attack vectors including malicious websites, compromised web applications, or even through phishing attacks that leverage the protocol inconsistency.
The vulnerability aligns with CWE-79, which specifically addresses cross-site scripting flaws in web applications, and can be categorized under the ATT&CK technique T1211 for "Exploitation for Defense Evasion" when attackers use XSS to bypass security controls. Organizations and users should prioritize updating to Apple iOS 9.3.3 and Safari 9.1.2 or later versions to address this vulnerability, as these releases include proper validation and sanitization of HTTP/0.9 responses within WebKit's JavaScript bindings. Additionally, network administrators should implement proper web filtering and monitoring solutions to detect and block suspicious HTTP/0.9 responses that may be indicative of exploitation attempts. The fix implemented by Apple addresses the root cause by ensuring that HTTP/0.9 responses are properly validated and sanitized before being processed by JavaScript bindings, preventing the injection of malicious content through protocol-level inconsistencies that previously allowed attackers to exploit this cross-protocol vulnerability.