CVE-2006-6238 in Safari
Summary
by MITRE
The AutoFill feature in Apple Safari 2.0.4 does not properly verify that all automatically populated form fields are visible to the user, which allows remote attackers to obtain sensitive information, such as usernames and passwords, via input fields of zero width, a variant of CVE-2006-6077.
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Analysis
by VulDB Data Team • 08/09/2018
The vulnerability described in CVE-2006-6238 represents a critical security flaw in Apple Safari 2.0.4's AutoFill functionality that directly violates fundamental principles of user interface security and information disclosure prevention. This issue stems from the browser's failure to properly validate the visibility state of form fields before automatically populating them with saved credentials, creating a significant attack vector that enables remote threat actors to harvest sensitive authentication data.
The technical implementation flaw occurs within Safari's AutoFill mechanism where the browser automatically fills form fields with previously stored user credentials without verifying whether these fields are actually visible to the user. Attackers can exploit this by crafting malicious web pages containing form fields with zero width or hidden visibility properties, which allows the AutoFill system to populate these invisible fields with usernames and passwords. The vulnerability specifically targets the browser's rendering and input validation logic, where the AutoFill feature operates under the assumption that all populated fields are accessible to the user, ignoring the fundamental security principle that sensitive information should only be exposed to legitimate users.
This vulnerability operates as a form of credential harvesting attack that leverages the browser's trust model and AutoFill automation features. The attack vector is particularly insidious because it exploits the user's expectation that AutoFill will only populate visible fields, while the browser's implementation fails to enforce proper visibility checks. The impact extends beyond simple information disclosure, as attackers can potentially capture complete authentication credentials including usernames, passwords, and other sensitive form data that would normally be protected by the browser's user interface constraints.
The operational implications of CVE-2006-6238 are severe for users of Safari 2.0.4, as it effectively undermines the security boundary between the browser's credential management system and malicious web content. This vulnerability creates a persistent threat vector that can be exploited across multiple websites and sessions, making it particularly dangerous for users who regularly save credentials in their browser's AutoFill system. The attack requires minimal technical skill from threat actors, as it only requires crafting a simple web page with invisible form fields, making it a widely exploitable security flaw.
From a cybersecurity perspective, this vulnerability aligns with CWE-200 (Information Disclosure) and represents a classic case of improper input validation where the system fails to verify the context and accessibility of input fields before processing automated data population. The issue also maps to ATT&CK technique T1555.003 (Credentials from Password Stores) and T1555.004 (Credentials from Web Browsers) as it enables attackers to extract credentials through browser-based mechanisms. The vulnerability demonstrates a critical failure in the browser's security architecture where the trust boundary between legitimate user interaction and automated credential filling is improperly enforced.
Mitigation strategies for CVE-2006-6238 require immediate browser updates to the latest Safari versions that address the AutoFill visibility validation flaw. Users should disable AutoFill functionality entirely for sensitive websites or enable additional security layers such as two-factor authentication to reduce the impact of credential theft. Browser vendors should implement more robust visibility checking mechanisms that ensure all AutoFill operations occur only within visible and accessible form fields. The vulnerability also highlights the importance of proper input validation and security boundary enforcement in browser security implementations, suggesting that similar checks should be implemented for all automated form population features to prevent similar issues in other browser implementations.