Privilege escalation in xen (Alpine package)

1) Privilege escalation

EUVDB-ID: #VU8202

Risk: Low

CVSSv3.1: 8.2 [CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H/E:F/RL:O/RC:C]

CVE-ID: CVE-2012-0217

CWE-ID: CWE-264 - Permissions, Privileges, and Access Controls

Exploit availability: Yes

Description

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.

Mitigation

Install update from vendor's website.

Vulnerable software versions

xen (Alpine package): 4.1.1-r2

CPE2.3

• cpe:2.3:o:alpine:xen_alpine_package:4.1.1-r2:*:*:*:*:alpine_linux:*:

External links

http://git.alpinelinux.org/aports/commit/?id=be9fdf040952f1d584775c20c39632a62de34c48
http://git.alpinelinux.org/aports/commit/?id=416d069cb4bfd802fe7566814f4c9870650d6c31

Q & A

Can this vulnerability be exploited remotely?

No. This vulnerability can be exploited locally. The attacker should have authentication credentials and successfully authenticate on the system.

Is there known malware, which exploits this vulnerability?

No. We are not aware of malware exploiting this vulnerability. However, a fully functional exploit for this vulnerability is available.