CVE-2015-5906 in iOS
Summary
by MITRE
The HTML form implementation in WebKit in Apple iOS before 9 does not prevent QuickType access to the final character of a password, which might make it easier for remote attackers to discover a password by leveraging a later prediction containing that character.
Be aware that VulDB is the high quality source for vulnerability data.
Analysis
by VulDB Data Team • 06/16/2022
The vulnerability described in CVE-2015-5906 represents a significant security flaw in Apple iOS versions prior to 9.0, specifically within the WebKit rendering engine's handling of HTML forms. This issue stems from the improper implementation of password field protection mechanisms that are designed to prevent unauthorized access to sensitive user input. The vulnerability exists in the QuickType predictive text functionality that operates across iOS devices, creating an exploitable condition where attackers can potentially reconstruct passwords through predictive text analysis.
The technical flaw manifests in how WebKit processes password fields within HTML forms, failing to adequately protect the final character of password inputs from QuickType prediction services. This occurs because the system does not properly isolate the last character of password fields from the predictive text engine's memory and suggestion algorithms. When users type passwords into web forms, the predictive text system retains information about the completed password in its memory, including the final character that might otherwise be protected. This creates a scenario where the predictive text system can suggest the final character as part of its prediction engine, making it easier for attackers to deduce complete passwords through pattern analysis and repeated predictions.
The operational impact of this vulnerability extends beyond simple password exposure, creating a persistent risk for users of affected iOS versions. Attackers can exploit this weakness by monitoring predictive text suggestions that appear after users enter passwords into web forms, particularly in scenarios where the predictive engine has cached information from previous password entries. This vulnerability specifically affects the security model of iOS's password handling, where the expectation is that password fields should be completely isolated from predictive text services to prevent any form of character leakage. The issue is particularly concerning in mobile environments where predictive text services are constantly learning from user input patterns, creating a long-term exposure window.
This vulnerability aligns with CWE-200, which addresses information exposure through improper information hiding, and represents a failure in proper input sanitization and field isolation. The attack vector follows patterns consistent with the ATT&CK framework's credential access techniques, particularly those involving predictive text exploitation and input analysis. The flaw demonstrates poor separation between user input handling and predictive services, creating an information leakage channel that violates fundamental security principles for password protection. Organizations and users affected by this vulnerability should prioritize immediate iOS updates to version 9.0 or later, where Apple implemented proper isolation of password fields from predictive text services. Additional mitigations include disabling predictive text features for password fields when available, using password managers that provide enhanced field protection, and implementing additional authentication layers such as multi-factor authentication to reduce the risk exposure from this specific vulnerability.
The broader implications of this vulnerability highlight the challenges in mobile security where predictive text services, designed for user convenience, can inadvertently create security weaknesses. This case demonstrates how seemingly benign features can become attack vectors when not properly integrated with security models. The vulnerability also underscores the importance of proper field type handling in web applications, as the issue stems from how WebKit interprets HTML form attributes and their corresponding security implications. Security professionals should consider this vulnerability as an example of how mobile operating system security models must account for predictive services and their potential interactions with sensitive input fields.