Apple's iTunes 10.5.1 update addresses a weakness in the application's update mechanism that could be exploited to trick users into visiting malicious websites.
The vulnerability stems from older iTunes versions use of plain HTTP requests to query Apple's servers for new updates. Because such connections lack encryption, a network attacker could intercept the requests and respond with rogue update URLs.
This man-in-the-middle technique is not new and has been thoroughly discussed in the security research community during the last few years. In order to ensure that an updating process is secure, companies must use encrypted connections, and in the case of auto-updates, they must also enforce code signing.
This particular attack scenario can only take place when iTunes is installed on a Windows system and the Apple Software Update component is not present.
The download button displayed by iTunes when an update is available normally launches this component, which is a dedicated tool for downloading and installing updates for the company's products. If it is not available, an update download URL is opened in the system's default browser.
This behavior offers a strong opportunity for social engineering attacks, because hackers can spoof Apple's website to serve a malicious file. Furthermore, the rogue Web page can be configured to exploit an unpatched vulnerability in a browser plug-in or the browser itself to download a malicious file without user interaction.
In iTunes 10.5.1, Apple uses HTTPS (HTTP Secure) connections to check for updates, making it impossible for attackers to modify the responses. Mac users are not affected by the flaw because Apple Software Update is included in Apple's operating system by default.
In addition to addressing this man-in-the-middle vulnerability, iTunes 10.5.1 also introduces iTunes Match, Apple's new cloud-based music file matching service.