Subject: [ASA-201705-16] openvpn: denial of service

Arch Linux Security Advisory ASA-201705-16
==========================================

Severity: High
Date    : 2017-05-13
CVE-ID  : CVE-2017-7478 CVE-2017-7479
Package : openvpn
Type    : denial of service
Remote  : Yes
Link    : https://security.archlinux.org/AVG-271

Summary
=======

The package openvpn before version 2.4.2-1 is vulnerable to denial of
service.

Resolution
==========

Upgrade to 2.4.2-1.

# pacman -Syu "openvpn>=2.4.2-1"

The problems have been fixed upstream in version 2.4.2.

Workaround
==========

The most severe vulnerability, CVE-2017-7478, which allows a remote
unauthenticated attacker to cause a denial of service, can be mitigated
by setting up tls-auth or tls-crypt. Note that this requires changing
both server and clients configurations.

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

- CVE-2017-7478 (denial of service)

A security issue has been found in OpenVPN <= 2.4.1 where an
unauthenticated attacker can send a packet with an unexpected payload
size during SSL handshake, causing a server shutdown. Servers using
tls-auth are protected against this attack as packets with an invalid
HMAC are discarded before being processed by the vulnerable code.

- CVE-2017-7479 (denial of service)

A security issue has been found in OpenVPN <= 2.4.1 where an
authenticated attacker can crash a server using an AEAD mode cipher by
sending crafted data to exhaust the packet counter.

Impact
======

A remote, unauthenticated attacker can crash a server not using tls-
auth or tls-crypt by sending a packet with an unexpected payload size.
A remote, authenticated attacker can crash a server using an AEAD mode
cipher by sending crafted data to exhaust the packet counter.

References
==========

https://community.openvpn.net/openvpn/wiki/QuarkslabAndCryptographyEngineerAudits
https://ostif.org/the-openvpn-2-4-0-audit-by-ostif-and-quarkslab-results/
http://blog.quarkslab.com/security-assessment-of-openvpn.html
https://security.archlinux.org/CVE-2017-7478
https://security.archlinux.org/CVE-2017-7479