This Metasploit module exploits a vulnerability in the FreeBSD kernel, when running on 64-bit Intel processors. By design, 64-bit processors following the X86-64 specification will trigger a general protection fault (GPF) when executing a SYSRET instruction with a non-canonical address in the RCX register. However, Intel processors check for a non-canonical address prior to dropping privileges, causing a GPF in privileged mode. As a result, the current userland RSP stack pointer is restored and executed, resulting in privileged code execution.
f1711c3320d7c4e9f80661d007057fb1b0b673f47fb51ec2968a821bc6aa8991FreeBSD Security Advisory - Not all information in the struct ptrace_lwpinfo is relevant for the state of any thread, and the kernel does not fill the irrelevant bytes or short strings. Since the structure filled by the kernel is allocated on the kernel stack and copied to userspace, a leak of information of the kernel stack of the thread is possible from the debugger. Some bytes from the kernel stack of the thread using ptrace(PT_LWPINFO) call can be observed in userspace.
533301518e00c3f677f362cc8de2e076480df8e74a46065791d33281d67d52f2FreeBSD Security Advisory - The FreeBSD operating system implements a rings model of security, where privileged operations are done in the kernel, and most applications request access to these operations by making a system call, which puts the CPU into the required privilege level and passes control to the kernel. FreeBSD/amd64 runs on CPUs from different vendors. Due to varying behaviour of CPUs in 64 bit mode a sanity check of the kernel may be insufficient when returning from a system call. Successful exploitation of the problem can lead to local kernel privilege escalation, kernel data corruption and/or crash.
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