SB2012061213 - SUSE Linux update for Xen
Published: June 12, 2012
Breakdown by Severity
- Low
- Medium
- High
- Critical
Description
This security bulletin contains information about 3 secuirty vulnerabilities.
1) Privilege escalation (CVE-ID: CVE-2012-0217)
The vulnerability allows a local user to escalate privileges on the system.
The vulnerability exists due to Intel processors sysret to non-canonical address behavior. This is a vulnerability following from a difference of behaviour of sysret in Intel's version of the amd64 architecture, em64t.
System calls may be implemented as using the em64t syscall/sysret instruction pair.
syscall saves the context of the calling unprivileged process before executing a system call in kernel mode; sysret restores it and resumes ordinary operations in user mode.
In the Intel implementation of sysret, if you have invalid information about the "next instruction" address in your saved context, the sysret instruction will trigger a trap in kernel space. However the sysret instruction is executed with the user stack pointer already loaded, so the kernel fault frame is written to the user stack. The kernel is unable to safely recover from this, so must ensure that the trap doesn't happen.
If your invalid "next instruction" address is in kernel space or in user space (and in the latter case, not where your program is) the program will segfault or execute attacker controlled code. If it is in the gap between user space and kernel space, the CPU will reset, except if someone managed to seed the address location with a valid instruction.
Successful exploitation of the vulnerability may allow an attacker to gain root access to the affected system.
2) Input validation error (CVE-ID: CVE-2012-0218)
The vulnerability allows a remote non-authenticated attacker to perform service disruption.
Xen 3.4, 4.0, and 4.1, when the guest OS has not registered a handler for a syscall or sysenter instruction, does not properly clear a flag for exception injection when injecting a General Protection Fault, which allows local PV guest OS users to cause a denial of service (guest crash) by later triggering an exception that would normally be handled within Xen.
3) Input validation error (CVE-ID: CVE-2012-2934)
The vulnerability allows a remote non-authenticated attacker to perform service disruption.
Xen 4.0, and 4.1, when running a 64-bit PV guest on "older" AMD CPUs, does not properly protect against a certain AMD processor bug, which allows local guest OS users to cause a denial of service (host hang) via sequential execution of instructions across a non-canonical boundary, a different vulnerability than CVE-2012-0217.
Remediation
Install update from vendor's website.