Shorewall: Security policy bypass

1. Gentoo Linux Security Advisory

Advisory Reference	GLSA 200507-20 / shorewall
Release Date	July 22, 2005
Latest Revision	September 14, 2005: 02
Impact	low
Exploitable	remote

Package	Vulnerable versions	Unaffected versions	Architecture(s)
net-firewall/shorewall	<= 2.4.1	>= 2.4.2	All supported architectures

Related bugreports: #99398

Synopsis

A vulnerability in Shorewall allows clients authenticated by MAC address filtering to bypass all other security rules.

2. Impact Information

Background

Shorewall is a high level tool for configuring Netfilter, the firewall facility included in the Linux Kernel.

Description

Shorewall fails to enforce security policies if configured with "MACLIST_DISPOSITION" set to "ACCEPT" or "MACLIST_TTL" set to a value greater or equal to 0.

Impact

A client authenticated by MAC address filtering could bypass all security policies, possibly allowing him to gain access to restricted services. The default installation has MACLIST_DISPOSITION=REJECT and MACLIST_TTL=(blank) (equivalent to 0). This can be checked by looking at the settings in /etc/shorewall/shorewall.conf

3. Resolution Information

Workaround

Set "MACLIST_TTL" to "0" and "MACLIST_DISPOSITION" to "REJECT" in the Shorewall configuration file (usually /etc/shorewall/shorewall.conf).

Resolution

All Shorewall users should upgrade to the latest available version:

Code Listing 3.1: Resolution

# emerge --sync
# emerge --ask --oneshot --verbose net-firewall/shorewall

4. References

Page updated July 22, 2005

Summary: This is a Gentoo Linux Security Advisory

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