Arch Linux Security Advisory ASA-201811-11
=========================================
Severity: Critical
Date    : 2018-11-07
CVE-ID  : CVE-2018-15686 CVE-2018-15687 CVE-2018-15688
Package : systemd
Type    : multiple issues
Remote  : Yes
Link    : https://security.archlinux.org/AVG-789

Summary
======
The package systemd before version 239.300-1 is vulnerable to multiple
issues including arbitrary code execution and privilege escalation.

Resolution
=========
Upgrade to 239.300-1.

# pacman -Syu "systemd>=239.300-1"

The problems have been fixed upstream in version 239.300.

Workaround
=========
- CVE-2018-15688

Disable IPv6 by setting either LinkLocalAddressing=ipv4 or
LinkLocalAddressing=no in the corresponding network configuration file.

Description
==========
- CVE-2018-15686 (privilege escalation)

A security issue has been found in systemd up to and including 239,
where the use of fgets() allows an attacker to escalate privilege via a
crafted service with NotifyAccess.

- CVE-2018-15687 (privilege escalation)

A security issue has been found in systemd up to and including 239,
where a race condition in the chown_one() function can be used to
escalate privileges via a crafted symlink.

- CVE-2018-15688 (arbitrary code execution)

An out-of-bounds write has been found in the dhcpv6 option handing code
of systemd-networkd up to and including v239.

It was discovered that systemd-network does not correctly keep track of
a buffer size  in the dhcp6_option_append_ia() function, when
constructing DHCPv6 packets. This flaw may lead to an integer underflow
that can be used to produce an heap-based buffer overflow. A malicious
host on the same network segment as the victim's one may advertise
itself as a DHCPv6 server and exploit this flaw to cause a Denial of
Service or potentially gain code execution on the victim's machine. The
overflow can be triggered relatively easy by advertising a DHCPv6
server with a server-id >= 493 characters long.

Impact
=====
A remote attacker is able to cause arbitrary code execution by
advertising itself as a DHCPv6 server with a specially crafted server-
id. A local attacker can escalate privileges with a specially crafted
service or a crafted symlink.

References
=========
https://bugs.archlinux.org/task/60609
https://bugs.chromium.org/p/project-zero/issues/detail?id=1687
https://bugs.launchpad.net/ubuntu/+source/systemd/+bug/1796402
https://github.com/systemd/systemd/pull/10447
https://github.com/systemd/systemd/pull/10450
https://bugs.chromium.org/p/project-zero/issues/detail?id=1689
https://bugs.launchpad.net/ubuntu/+source/systemd/+bug/1796692
https://github.com/systemd/systemd/pull/10517
https://bugs.launchpad.net/ubuntu/%2Bsource/systemd/%2Bbug/1795921
https://github.com/systemd/systemd/pull/10518
https://github.com/poettering/systemd/commit/49653743f69658aeeebdb14faf1ab158f1f2cb20
https://security.archlinux.org/CVE-2018-15686
https://security.archlinux.org/CVE-2018-15687
https://security.archlinux.org/CVE-2018-15688