Even the most securely coded piece of software can be susceptible to malicious hacking and significant exploits the moment it's linked with less-secure applications or platforms. These multiproduct, multirole exploits (also known as "chained exploits") are among the most difficult security issues to prevent. In fact, though issues may be known, they can be just as challenging to avert.
Two recent security events -- one involving net/tun and a Linux compiler and the second involving Gmail, Hotmail, and Twitter -- illustrate the challenges that chained exploits create. As I wrote last week in regard to the forthcoming Google Chrome OS, most -- if not all -- software must interact with other products and features if it's going to deliver the functionality that users demand. The trade-off can be weakened security.
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The Linux kernel vulnerability emerged in the open source net/tun program. In this case, the bug was not written in to the net/tun program. Rather, when the program's source code is run through a Linux compiler for optimization, the complier introduces a kernel exploit. In particular, the compiler finds what it thinks is an unnecessary NULL value and removes an important IF-THEN statement. The subsequent exploits work even against improved security versions of Linux, such as SeLinux (see a video of a representative exploit).
The second example of a chained exploit is even more intriguing. In this case, a malicious hacker broke in to one or more Twitter employees' e-mail accounts, then publicly posted both personal and company confidential information.
The hacker accomplished this feat after discovering that a Twitter employee used Gmail and that a request for a new password for the account would be sent to the employee's Hotmail account. However, the employee had not used the Hotmail account in a very long time, so their Hotmail address was available for anyone to adopt.