AUDIT Target Support

AUDIT Target Support Tom Eastep 2011 Thomas M. Eastep Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation; with no Invariant Sections, with no Front-Cover, and with no Back-Cover Texts. A copy of the license is included in the section entitled GNU Free Documentation License.

Background In early 2011, Thomas Graf submitted a set of patches to the Netfilter development list that implemented an AUDIT rule target. This is from the initial submittal:

This patch adds a new netfilter target which creates audit records for packets traversing a certain chain. It can be used to record packets which are rejected administraively as follows: -N AUDIT_DROP -A AUDIT_DROP -j AUDIT --type DROP -A AUDIT_DROP -j DROP A rule which would typically drop or reject a packet would then invoke the new chain to record packets before dropping them. -j AUDIT_DROP The module is protocol independant and works for iptables, ip6tables and ebtables. netfilter hook packet length incoming/outgoing interface MAC src/dst/proto for ethernet packets src/dst/protocol address for IPv4/IPv6 src/dst port for TCP/UDP/UDPLITE icmp type/code

The audited packets are sent to a daemon (auditd) that write the audit information to a log file. In a related post by Eric Paris, the following additional information was posted:

AUDIT exists because a very large number of gov't customers (Not just USA) have special requirements about how 'relevant' information is gathered and stored. They require centralization and standardization and require pretty formal documentation describing it's operation. The gov't certification authority has recently added a requirement that they be able to log 'illegal attempted network connections' via the approved audit facility. Thus, this patch.

The AUDIT target was included in Linux kernel 2.6.39.

Shorewall Support Shorewall support for the AUDIT target was added in 4.4.20. The support involves the following: A new "AUDIT Target" capability is added and is required for auditing support. To use AUDIT support with a capabilities file, that file must be generated using this or a later release. Use 'shorewall show capabilities' after installing this release to see if your kernel/iptables support the AUDIT target. In /etc/shorewall/policy's POLICY column, the policy (and default action, if any) may be followed by ':audit' to cause application of the policy to be audited. Only ACCEPT, DROP and REJECT policies may be audited. Example: #SOURCE DEST POLICY LOG # LEVEL net fw DROP:audit It is allowed to also specify a log level on audited policies resulting in both auditing and logging. Three new builtin targets that may be used in the rules file, in macros and in other actions. A_ACCEPT - Audits and accepts the connection request A_DROP - Audits and drops the connection request A_REJECT - Audits and rejects A log level may be supplied with these actions to provide both auditing and logging. Example: #ACTION SOURCE DEST PROTO A_ACCEPT:info loc net ... The BLACKLIST_DISPOSITION, MACLIST_DISPOSITION, SMURF_DISPOSITION and TCP_FLAGS_DISPOSITION options may be set as follows: BLACKLIST_DISPOSITION A_DROP or A_REJECT MACLIST_DISPOSITION A_DROP, A_REJECT unless MACLIST_TABLE=mangle SMURF_DISPOSITION This option was added in Shorewall 4.4.20 A_DROP TCP_FLAGS_DISPOSITION A_DROP or A_REJECT An 'audit' option has been added to the /etc/shorewall/blacklist file which causes the packets matching the entryto be audited. 'audit' may not be specified together with 'accept'. The builtin actions (dropBroadcast, rejNonSyn, etc.) now support an 'audit' parameter which causes all ACCEPT, DROP and REJECTs performed by the action to be audited. This allows creation of audited versions of the Shorewall-provided default actions (action.Drop and action.Reject). The builtin actions are those actions listed in the output of shorewall show actions whose names begin with a lower-case letter. Here's a version of action.Drop that does auditing: #TARGET SOURCE DEST PROTO DPORT SPORT # # Count packets that come through here # COUNT # # Reject 'auth' # A_REJECT - - tcp # # Don't log broadcasts # dropBcast(audit) # # ACCEPT critical ICMP types # AudAllowICMPs - - icmp # # Drop packets that are in the INVALID state -- these are usually ICMP packets # and just confuse people when they appear in the log. # dropInvalid(audit) # # Drop Microsoft noise so that it doesn't clutter up the log. # AudSMB(DROP) AudDropUPnP # # Drop 'newnotsyn' traffic so that it doesn't get logged. # dropNotSyn(audit) - - tcp # # Drop late-arriving DNS replies. These are just a nuisance and clutter up # the log. # A_DROP - - udp - 53 The 'Aud...' macros would be auditing versions of their standard macro counterparts (if you are interested in auditing those connection types).