CVE-2009-2072 in Safari
Summary
by MITRE
Apple Safari does not require a cached certificate before displaying a lock icon for an https web site, which allows man-in-the-middle attackers to spoof an arbitrary https site by sending the browser a crafted (1) 4xx or (2) 5xx CONNECT response page for an https request sent through a proxy server.
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Analysis
by VulDB Data Team • 08/11/2021
The vulnerability described in CVE-2009-2072 represents a critical security flaw in Apple Safari's handling of SSL/TLS certificate validation during HTTPS connections. This issue specifically affects how Safari displays visual security indicators to users, creating a deceptive environment where attackers can manipulate the browser's certificate validation process. The flaw enables man-in-the-middle attacks by exploiting Safari's failure to properly verify certificate caching before presenting security indicators to users.
The technical implementation of this vulnerability stems from Safari's improper certificate validation mechanism when processing HTTPS requests through proxy servers. When a user attempts to access an HTTPS site, Safari should verify that the certificate presented by the server is valid and properly cached before displaying the security lock icon. However, the browser's implementation allows attackers to craft specific 4xx or 5xx CONNECT response pages that can trick Safari into displaying the lock icon even when the connection is not properly secured. This occurs because the browser's certificate validation process does not adequately check whether a cached certificate exists before making security visual indicators available to users.
The operational impact of this vulnerability is significant as it fundamentally undermines the trust model that users place in visual security indicators within web browsers. Attackers can exploit this flaw by positioning themselves between the user and the target website through proxy servers, then crafting malicious responses that appear to be legitimate HTTPS connections. This allows them to intercept, modify, or redirect user traffic while maintaining the illusion of secure communication. The vulnerability particularly affects users who rely on Safari's visual security indicators to determine the legitimacy of their connections, potentially leading to credential theft, data interception, and other malicious activities.
This vulnerability aligns with CWE-295, which addresses improper certificate validation, and relates to ATT&CK technique T1573.002, which covers protocol tunneling through proxy servers. The flaw demonstrates how browser security mechanisms can be circumvented through manipulation of HTTP response codes and proxy handling, creating a dangerous trust relationship between users and potentially compromised connections. The vulnerability also connects to broader security concerns around certificate pinning and the reliability of browser-based security indicators, highlighting the importance of proper certificate validation before displaying security visual cues to users.
Mitigation strategies for this vulnerability involve ensuring that Safari properly validates certificate caching before displaying security indicators, implementing more robust certificate verification mechanisms, and updating proxy handling code to prevent manipulation of connection status indicators. Organizations should also consider implementing additional security measures such as certificate pinning, monitoring for suspicious proxy behavior, and educating users about the limitations of visual security indicators. Regular browser updates and security patches are essential to address this type of vulnerability, as the flaw represents a fundamental issue in how Safari processes certificate validation during HTTPS connections. The vulnerability serves as a reminder of the critical importance of proper certificate validation in maintaining secure communications and the potential consequences when browsers fail to adequately verify security credentials before presenting trust indicators to users.