The vulnerabilities could allow attackers with access to limited user accounts to gain administrator privileges.
For the third time in less than six months security issues have forced Lenovo to update one of the tools preloaded on its PCs.
Last week, the company released version 5.07.0019 of Lenovo System Update, a tool that helps users keep their computers' drivers and BIOS up to date and which was previously called ThinkVantage System Update. The new version fixes two local privilege escalation vulnerabilities discovered by researchers from security firm IOActive.
One of the vulnerabilities is located in the tool's help system and allows users with limited Windows accounts to start an instance of Internet Explorer with administrator privileges by clicking on URLs in help pages. That's because Lenovo System Update itself runs under a temporary administrator account that the application creates when installed, so any process it spawns will run under the same account.
"From there, an unprivileged attacker has many ways to exploit the web browser instance running under Administrator privileges to elevate his or her own privileges to Administrator or SYSTEM," IOActive security researcher Sofiane Talmat said in a blog post Wednesday.
The second vulnerability is also related to the temporary administrator account and particularly to the way in which its name and password are generated.
The username follows the pattern tvsu_tmp_xxxxxXXXXX, where each lowercase x is a randomly generated lower case letter and each uppercase X is a randomly generated uppercase letter. However, the function that's supposed to randomly choose the letters is tied to the current time, making its output predictable.
"It is possible for an attacker to regenerate the same username based on the time the account was created," Talmat said.
The password generation function uses two methods, a secure one and a fallback one that's also predictable. This means that in certain situations an attacker could guess both the username and password and gain administrative privileges.
Lenovo System Update received two other security patches this year: one in July and one in October. Those updates fixed vulnerabilities that could have allowed attackers to execute commands through the application or to replace legitimate updates with malware.