CVE-2011-3432 in iOS
Summary
by MITRE
The UIKit Alerts component in Apple iOS before 5 allows remote attackers to cause a denial of service (device hang) via a long tel: URL that triggers a large size for the acceptance dialog.
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Analysis
by VulDB Data Team • 11/24/2021
The vulnerability identified as CVE-2011-3432 represents a classic denial of service flaw within Apple iOS operating systems prior to version 5. This issue specifically affects the UIKit Alerts component which is responsible for displaying user interface elements including alert dialogs and confirmation prompts. The vulnerability manifests when the system processes a malformed tel: URL that contains an excessively long phone number string, causing the device to hang during the display of the acceptance dialog. This type of vulnerability falls under the category of improper input validation and demonstrates how seemingly benign URL schemes can be exploited to disrupt system operations. The flaw represents a significant security concern as it can be triggered remotely through web content or malicious applications, potentially affecting millions of iOS devices in the wild.
The technical implementation of this vulnerability stems from inadequate bounds checking within the iOS URL handling mechanism. When a tel: URL is processed by the system, the UIKit framework attempts to display a confirmation dialog to the user before initiating a phone call. However, the framework fails to properly validate the length of the phone number portion of the URL, allowing attackers to craft URLs with excessively long numeric strings. This causes the system to allocate memory and process the dialog display with an impossibly large data set, leading to resource exhaustion and ultimately device hang. The vulnerability is particularly concerning because it operates at the user interface level, meaning that even simple web browsing could trigger the condition without requiring any special privileges or complex attack vectors. This behavior aligns with CWE-129, which describes improper validation of length of input buffers, and demonstrates how UI components can become attack surfaces when proper input sanitization is omitted.
The operational impact of this vulnerability extends beyond simple device inconvenience, as it represents a potential vector for more sophisticated attacks within the broader context of mobile security. An attacker could potentially use this vulnerability as a stepping stone for other exploits or as part of a larger campaign targeting iOS devices. The device hang condition could be exploited to create a reliable denial of service condition that affects user productivity and could be leveraged in targeted attacks against specific individuals or organizations. From an attacker perspective, this vulnerability aligns with ATT&CK technique T1499.004 which covers network denial of service attacks, and T1566.002 which involves phishing attacks through web content. The vulnerability's remote exploitability means that users could be affected simply by visiting compromised websites or receiving malicious links through various communication channels. The impact on enterprise environments is particularly significant as it could be used to disrupt business operations or as part of social engineering campaigns targeting mobile workforce users.
Mitigation strategies for this vulnerability primarily involve updating to iOS version 5 or later, where Apple implemented proper bounds checking and input validation for tel: URL processing. System administrators should ensure that all iOS devices within their environment are updated to the latest available versions to prevent exploitation. Additionally, network administrators can implement URL filtering and content inspection mechanisms to block or sanitize tel: URLs before they reach end-user devices. Security monitoring should include detection of unusual network traffic patterns that might indicate attempts to exploit this vulnerability. Organizations should also consider implementing mobile device management solutions that can enforce security policies and ensure timely patch deployment. The vulnerability serves as a reminder of the importance of input validation across all system components, including user interface elements, and demonstrates how seemingly simple functions can become security risks when proper validation is not implemented. Organizations should also review their incident response procedures to ensure they can quickly identify and respond to similar vulnerabilities that may affect their mobile device populations.