[arch-security] [ASA-201709-21] openvpn: arbitrary code execution

[Levente Polyak]

Arch Linux Security Advisory ASA-201709-21
==========================================

Severity: Medium
Date    : 2017-09-28
CVE-ID  : CVE-2017-12166
Package : openvpn
Type    : arbitrary code execution
Remote  : Yes
Link    : https://security.archlinux.org/AVG-420

Summary
=======

The package openvpn before version 2.4.4-1 is vulnerable to arbitrary
code execution.

Resolution
==========

Upgrade to 2.4.4-1.

# pacman -Syu "openvpn>=2.4.4-1"

The problem has been fixed upstream in version 2.4.4.

Workaround
==========

Ensure 'key-method 2' is used (default value).

Description
===========

The bounds check in the read_key() function in OpenVPN before 2.4.4 and
2.3.18 was performed after using the value, instead of before.  If
'key-method 1' is used, this allowed an attacker to send a malformed
packet to trigger a stack buffer overflow.
Note that 'key-method 1' has been replaced by 'key method 2' as the
default in OpenVPN 2.0 (released on 2005-04-17), and explicitly
deprecated in 2.4 and marked for removal in 2.5. This should limit the
amount of users impacted by this issue.

Impact
======

A remote attacker is able to execute arbitrary code on the affected
host when an old key-method is configured.

References
==========

https://community.openvpn.net/openvpn/wiki/CVE-2017-12166
https://github.com/OpenVPN/openvpn/commit/3b1a61e9fb27213c46f76312f4065816bee8ed01
https://security.archlinux.org/CVE-2017-12166

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