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Rufus, the open source software developed by Akeo Consulting, is an application used on Microsoft Windows platforms to create and format bootable USB flash drives. Due to a vulnerability disclosed in August 2017, Rufus failed to update itself when creating a bootable USB flash drive. What are the risks of this Rufus vulnerability? How can security teams fix the problem?
Because of this Rufus software vulnerability, an authenticated attacker could subvert the update process while creating a bootable flash drive. This made it possible for an attacker to execute arbitrary code on a vulnerable system.
Windows XP or later can be used to download bootable ISO images to boot up different operating systems -- including Windows, Linux, FreeDOS, Kubuntu and Unified Extensible Firmware Interface, which is an alternative to basic input/output systems (BIOS). If an operating system (OS) is already installed on a laptop or desktop, the bootable flash drive can be treated as a device in the BIOS system.
The order of the bootable devices -- including the CD drive -- may need to be changed in the system BIOS to ensure the OS on the flash drive boots when it is selected from a menu of multiple OSes. The bootable flash drive should have a higher priority than the CD drive.
Rufus software version 2.16 has built-in update capabilities that enable automatic retrieval of updates over HTTP. This version attempts to perform some basic signature checking of downloaded updates. One drawback, however, is the software isn't able to securely install updates over HTTP.
Because Rufus uses HTTP instead of HTTPS, there's no way to ensure the update has been signed by a trusted certificate authority that certifies the ownership of a public key by the named subject of the certificate. This could enable an attacker to self-sign his own certificate to perform arbitrary code execution on an untrusted network, such as public Wi-Fi.
The attacker needs to be on the same network as other Rufus software users to be in a position to affect network traffic. This increases the chance of a man-in-the-middle attack.
To stay ahead of attackers, organizations should use web browsers to obtain updates directly from the Rufus website and should avoid untrusted networks. The Rufus website uses HTTPS rather than HTTP, which secures communication over the internet. However, more work is necessary to fully secure Rufus software.
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