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Manual Reference Pages  -  ABCK (1)


abck - Process intrusion attempts found in the system log.


Record Processing
Bugs And Misfeatures
Copyright And Licensing


abck [-dehilmsv]


'abck' is an interactive tool to examine intrusion attempts and decide what, if anything, to do about them. It reads through /var/log/messages looking for evidence of an intrusion attempt. Upon finding such a record, 'abck' qualifies it against information supplied by the user on the command line to determine if the record is to be processed. As packaged, 'abck' handles several common types of intrusion attempt records, but it can easily be expanded to handle others.

'abck' determines whether the record contains the name or IP address of the source of the attack. If it finds an IP address, it will attempt to reverse the address into a name. If it cannot find a legitimate reverse, it will try to find the authority responsible for that address.

Each matching record is presented to the user. The user can do a 'whois ' lookup on the record, pick or edit the domain name that will be notified about the attack attempt, permanently forget the record without processing it, skip the record, or quit the program.

Once the user has selected the domain to be notified (i.e., they did not skip or forget a given record), 'abck' formats and sends an email to the 'abuse' and 'root' accounts at that domain, notifying them of the intrusion attempt. This email is also sent to the 'root' user on the machine that was invaded. The email contains all the relevant information about the machine which was attacked and appends a copy of the log record containing evidence of the attempt.

Very often, an intruder will try several different means of entry, thereby generating multiple log events. This is common, for example, if an attacker is running a port scanning program. As 'abck' runs , it keeps track of the attackers for which the user sends a notification email. (The user may not necessarily send an email for each and every intrusion attempt.) If 'abck' sees this intruder’s host name/address again later in the log, it will automatically send the notification to the same place as the user originally selected without any user interaction.

'abck' keeps track of the records that the user has either processed (by sending an email notification) or 'forgotten' (see below). These records will not appear again in subsequent invocations of 'abck' (except with the -s option; all matching records are displayed, even if they’ve previously been processed). This information is kept in $HOME/.abck_history.

You may also specify a list of IPs or hostnames which 'abck' is to ignore by default. This is useful when you do not wish to process "attacks" from friendly locations or you wish to ignore intrusion attempts from particular hosts for some other reason. You can override this default behavior using the -i and -l command line switches.

For details on how to specify what you want ignored, see the "FILES" section below.


-d # Only go back # days in the log.

-e string
  Only process attack records which do not contain 'string'.

-h Display help information.

-i Do not ignore the IPs/Hostnames found specified in ~/.abck_ignored Mutually exclusive with -l option. Last one on command line is obeyed.

-l List ignored records as they are encountered. List all ignored IPs/Hostnames at the end of the program run. Mutually exclusive with -i option. Last one on command line is obeyed.

-m string
  Only process attack records if they contain 'string'.

-s Don’t actually process the matching records, just display them.

-v Display detailed version information.


Each time the record of an intrusion attempt is found which matches the command line-selected constraints, it is presented to the user for disposition. A typical prompt looks like this:

Log Record:
 Matching log entry found in /var/log/messages

Who Gets Message For: <>? []

Pressing 'Enter' accepts the default notification destination of ''. Email is thus sent to '', '', and 'root@local.machine...'. 'abck' then moves on to the next log entry.

Notice that this is the only way to actually send a notification email. The commands below allow the user to modify the notification domain, but only when the user responds with a blank line, will email actually be sent.

The user can also issue a number of commands at the prompt to do further lookups on the attacker or modify the domain to be notified.


Forget this record entirely without processing it. This means it will not show up again in subsequent runs of 'abck'.

l Move left one subdomain in the default destination.

q Quit the program. This causes an immediate exit. No history information is written to disk, even if some records have been processed and notification sent.

r Move right one subdomain in the default destination. 'abck' will prevent the user from doing this beyond the point there are less than two domains showing. (A user can enter a destination with only one level of domain manually. This is useful for testing because it allows 'localhost' to be entered as the point of notification.)

s Skip this record for now. The next time 'abck' is run, this record will be presented the user again for disposition.

w Run a 'whois' lookup on the address/name found in the original log entry. This is helpful when reverse lookups fail and may provide further information about the origin of the attack.

Any other string
  Replace the current default domain to notify with this string.


As 'abck' scans the system log, it looks for two keywords: 'refused' and 'unauthorized'. If it finds any of these keywords anywhere in a given log record, it presents that record to the user for disposition.

You can trivially add other 'trigger words' to the list of things 'abck' looks for as signs of intrusion. Suppose you have an intrusion detection program which writes log records like this:

Jul 27 00:27:35 eskimo inetd[56691]: Intruder foiled

To get 'abck' to present records like this to the user for disposition, you only need two things. First, you need a unique trigger word that only appears in records of this type, say, 'foiled'. Then, you need to know which field within that record contains either the host name or IP address of the attacker. The first field is 0, so in this example, it would be field 7.

To get 'abck' to recognize this type of record, merely add this information to the AttackKeys data structure in the program. This is a Python dictionary, so all entries are of the form:

"keyword" : Fieldnum,


~/.abck_history - History of all records user has either processed or forgotten.

~/.abck_ignored - List of all IPs or Hostnames you want to ignore by default. Must have only one entry per line with no whitespace or comment characters. You may enter partial entries so that they match multiple attacking hosts. The rule is that partial entries for IPs should be truncated on the right and partial entries for Hostnames should be truncated on the left. For example, 192.168.3 will ignore everything from - Similarly, the entry: will ignore any host in that domain regardless of the less signficant subdomains.


You must have a reasonably current copy of ’python’ installed for 'abck' to operate. Also, the 'dig' and 'whois' programs must be on the system in a directory somewhere in $PATH.


None known as of this release, but the code is getting kind of ugly from constant hacking. Maintenance is starting to be painful.


abck is Copyright(c) 2001, 2002 TundraWare Inc. For terms of use, see the abck-License.txt file in the program distribution. If you install abck on a FreeBSD system using the ’ports’ mechanism, you will also find this file in /usr/local/share/doc/abck.


Tim Daneliuk

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