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Source: https://bugs.chromium.org/p/project-zero/issues/detail?id=1091 This bug report describes two separate issues that, when combined, allow any user on a Linux host system on which VirtualBox is installed to gain code execution in the kernel. Since I'm not sure which one of these issues crosses something you consider to be a privilege boundary, I'm reporting them together. To reproduce, download the attached file virtualbox-host-r3-to-host-r0-crasher.tar, ensure that at least one VM is running, then: /tmp$ tar xf virtualbox-host-r3-to-host-r0-crasher.tar /tmp$ cd virtualbox-host-r3-to-host-r0-crasher/ /tmp/virtualbox-host-r3-to-host-r0-crasher$ ./attack.sh ./attack.sh: line 7: 82634 KilledQT_QPA_PLATFORM_PLUGIN_PATH=fake_qt_platform_plugins /usr/lib/virtualbox/VirtualBox --startvm /tmp/virtualbox-host-r3-to-host-r0-crasher$ dmesg [...] [279468.028025] BUG: unable to handle kernel paging request at 0000000013370028 [...] The first step of the attack is to get access to the device /dev/vboxdrv, which can normally only be opened by root: ~$ ls -l /dev/vboxdrv crw------- 1 root root 10, 54 Jan 17 16:23 /dev/vboxdrv In order to be able to open this device, the main VirtualBox binary is setuid root: $ ls -l /usr/lib/virtualbox/VirtualBox -r-s--x--x 1 root root 35240 Jan 16 19:55 /usr/lib/virtualbox/VirtualBox VirtualBox uses its root privileges to open /dev/vboxdrv, then quickly drops its privileges. However, it retains the open file descriptor to /dev/vboxdrv. Therefore, an attacker can gain access to the device /dev/vboxdrv by injecting code into a VirtualBox userspace process. After dropping privileges, VirtualBox loads various libraries, including QT, that are not designed to run in a setuid context. See https://doc.qt.io/qt-5/qcoreapplication.html#setSetuidAllowed : "Qt is not an appropriate solution for setuid programs due to its large attack surface." Using the environment variable QT_QPA_PLATFORM_PLUGIN_PATH, an attacker can let QT load a library from an arbitrary directory. The second step is to use the device /dev/vboxdrv to corrupt the kernel. The SUP_IOCTL_CALL_VMMR0 ioctl takes a pointer to a structure in ring 0 as an argument (pVMR0) and ends up calling the function VMMR0EntryEx(). With the attached PoC, this function crashes when attempting to read pVM->pVMR0. However, an attacker who supplies a pointer to attacker-controlled kernel memory could reach any point in the function. For some operations, e.g. VMMR0_DO_VMMR0_INIT, the attacker-controlled pointer pVM is then used in vmmR0CallRing3SetJmpEx() to save and restore various kernel registers, including RSP. By supplying a pointer to which the attacker can concurrently write data, an attacker can therefore control the kernel stack and thereby perform arbitrary operations in the kernel. (As far as I can tell, a comment in VMMR0EntryEx points out this issue: "/** @todo validate this EMT claim... GVM knows. */") Proof of Concept: https://gitlab.com/exploit-database/exploitdb-bin-sploits/-/raw/main/bin-sploits/41905.zip |
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