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| -rw-r--r-- | DEVELOP | 284 |
1 files changed, 149 insertions, 135 deletions
@@ -1,6 +1,6 @@ - __ _ _ ___ _ - / _|__ _(_) |_ ) |__ __ _ _ _ - | _/ _` | | |/ /| '_ \/ _` | ' \ + __ _ _ ___ _ + / _|__ _(_) |_ ) |__ __ _ _ _ + | _/ _` | | |/ /| '_ \/ _` | ' \ |_| \__,_|_|_/___|_.__/\__,_|_||_| ================================================================================ @@ -26,7 +26,7 @@ Pull Requests When submitting pull requests on GitHub we ask you to: * Clearly describe the problem you're solving; -* Don't introduce regressions that will make it hard for systems administrators +* Don't introduce regressions that will make it hard for systems administrators to update; * If adding a major feature rebase your changes on master and get to a single commit; * Include test cases (see below); @@ -42,74 +42,79 @@ Filters are tricky. They need to: * work with the range of logging configuration options available in the software; * work with multiple operating systems; -* not make assumptions about the log format in excess of the software (don't - assume a username doesn't contain spaces and use \S+ unless you've checked - the source code); -* make assumptions as to how future versions of the software will log messages - (guess what would happen to the log message if different authentication +* not make assumptions about the log format in excess of the software + (e.g. do not assume a username doesn't contain spaces and use \S+ unless + you've checked the source code); +* account for how future versions of the software will log messages + (e.g. guess what would happen to the log message if different authentication types are added); * not be susceptible to DoS vulnerabilities (see Filter Security below); and * match intended log lines only. Please follow the steps from Filter Test Cases to Developing Filter Regular -Expressions and submit a GitHub pull request afterwards. If you get stuck, -create a GitHub issue with what you have done and we'll attempt to help. +Expressions and submit a GitHub pull request (PR) afterwards. If you get stuck, +you can push your unfinished changes and still submit a PR -- describe +what you have done, what is the hurdle, and we'll attempt to help (PR +will be automagically updated with future commits you would push to +complete it). Filter test cases ----------------- Purpose: -Start by finding the log messages that the application generates related to +Start by finding the log messages that the application generates related to some form of authentication failure. If you are adding to an existing filter think about whether the log messages are of a similar importance and purpose -to the existing filter. If you are a user of fail2ban, and did a package -update of fail2ban that started matching the new log messages, would anything -unexpected happen? Would the bantime/findtime for the jail be appropriate for -the new log messages. If it doesn't perhaps it needs to be in a separate -filter definition, for example like exim is authentication failures and -exim-spam contains log messages related to spam. +to the existing filter. If you were a user of Fail2Ban, and did a package +update of Fail2Ban that started matching new log messages, would anything +unexpected happen? Would the bantime/findtime for the jail be appropriate for +the new log messages? If it doesn't, perhaps it needs to be in a separate +filter definition, for example like exim filter aims at authentication failures +and exim-spam at log messages related to spam. Even if it is a new filter you may consider separating the log messages into different filters based on purpose. Cause: -Are some of the log lines a result of the same action? For example is a PAM +Are some of the log lines a result of the same action? For example, is a PAM failure log message, followed by an application specific failure message the -result of the same user/script action. The result is if you add regular -expressions for both you'll end up with two failures for a single action. -Select the most appropriate log message and document the other log message with -a test case not to match it and a description as to why you chose one over -another. - -With the log lines selected consider what occurred to generate those log -messages and whether they could of been generated by accidental means. Could -the log message occur always as this is the first step towards the application +result of the same user/script action? If you add regular expressions for +both you would end up with two failures for a single action. +Therefore, select the most appropriate log message and document the other log +message) with a test case not to match it and a description as to why you chose +one over another. + +With the selected log lines consider what action has caused those log +messages and whether they could have been generated by accident? Could +the log message be occurring due to the first step towards the application asking for authentication? Could the log messages occur often? If some of these are true make a note of this in the jail.conf example that you provide. Samples: -Its important to include log file samples so any future change in the regular +It is important to include log file samples so any future change in the regular expression will still work with the log lines you have identified. -The sample log messages are provided in testcases/files/logs/ with same name -as the filter. Each log line should include a failJSON metadata (so the logs +The sample log messages are provided in a file under testcases/files/logs/ +named identically as the corresponding filter (but without .conf extension). +Each log line should be preceded by a line with failJSON metadata (so the logs lines are tested in the test suite) directly above the log line. If there is any specific information about the log message, such as version or an -application configuration option that is needed for the message to occur, +application configuration option that is needed for the message to occur, include this in a comment (line beginning with #) above the failJSON metadata. Log samples should include only one, definitely not more than 3, examples of log messages of the same form. If log messages are different in different -versions of the application log messages that show this is encouraged. +versions of the application log messages that show this are encouraged. -Also attempt inject an IP into the application so that fail2ban detects the IP +Also attempt to inject an IP into the application (e.g. by specifying +it as a username) so that Fail2Ban possibly detects the IP from user input rather than the true origin. See the Filter Security section and the top example in testcases/files/logs/apache-auth as to how to do this. -One you have discovered this correct the regex so it doesn't match and provide -this as a test case with match: false (see failJSON below). +One you have discovered that this is possible, correct the regex so it doesn't +match and provide this as a test case with "match": false (see failJSON below). If the mechanism to create the log message isn't obvious provide a configuration and/or sample scripts testcases/files/config/{filtername} and @@ -120,24 +125,25 @@ FailJSON metadata: A failJSON metadata is a comment immediately above the log message. It will look like: -# failJSON: { "time": "2013-06-10T10:10:59", "match": true , "host": "193.169.56.211" } +# failJSON: { "time": "2013-06-10T10:10:59", "match": true , "host": "93.184.216.119" } Time should match the time of the log message. It is in a specific format of -Year-Month-Day'T'Hour:minute:Second. If your log message does not include a -year, like the example below, the year will be 2005, if before Sun Aug 14 10am -UTC, and 2004 if afterwards. +Year-Month-Day'T'Hour:minute:Second. If your log message does not include a +year, like the example below, the year should be listed as 2005, if before Sun +Aug 14 10am UTC, and 2004 if afterwards. Here is an example failJSON +line preceding a sample log line: # failJSON: { "time": "2005-03-24T15:25:51", "match": true , "host": "198.51.100.87" } Mar 24 15:25:51 buffalo1 dropbear[4092]: bad password attempt for 'root' from 198.51.100.87:5543 -The host will contain the IP or domain that should be blocked. +The "host" in failJSON should contain the IP or domain that should be blocked. -For long lines that you don't want matched, like log injection vulnerabilities -and log lines excluded (see "Cause" section above), a "match": false in the -failJSON and the reason why in the comment above. +For long lines that you do not want to be matched (e.g. from log injection +attacks) and any log lines to be excluded (see "Cause" section above), set +"match": false in the failJSON and describe the reason in the comment above. -After developing the regexs, the following command will test all the failJSON -metadata against the log lines: +After developing regexes, the following command will test all failJSON metadata +against the log lines in all sample log files ./fail2ban-testcases testSampleRegex @@ -146,28 +152,29 @@ Developing Filter Regular Expressions Date/Time: -The first step in checking your log line can have a filter is to check that the -time format matches an existing regex. To test this copy the time component -from the log line and append an IP address. Then test it with: +At the moment, Fail2Ban depends on log lines to have time stamps. That is why +before starting to develop failregex, check if your log line format known to +Fail2Ban. Copy the time component from the log line and append an IP address to +test with following command: ./fail2ban-regex "2013-09-19 02:46:12 1.2.3.4" "<HOST>" -In the output from this should be something like: +Output of such command should contain something like: Date template hits: |- [# of hits] date format | [1] Year-Month-Day Hour:Minute:Second -Ensure that the template description matches of bits in the time format. If -there isn't a matched a format and date regex can be added to -server/datedetector.py. Ensure this is added in an order that will match make -more specific matches occur first and that their is no confusion as to which -is the date or month. +Ensure that the template description matches time/date elements in your log line +time stamp. If there is no matched format then date template needs to be added +to server/datedetector.py. Ensure that a new template is added in the order +that more specific matches occur first and that there is no confusion between a +Day and a Month. Filter file: -The filter file is in config/filter.d/{filtername}.conf. The format of the -filter file has two sections INCLUDES and Definition as follows: +The filter is specified in a config/filter.d/{filtername}.conf file. Filter file +can have sections INCLUDES (optional) and Definition as follows: [INCLUDES] @@ -181,30 +188,31 @@ failregex = .... ignoreregex = .... -This is also documented in the man pages as jail.conf (section 5). Other -definitions can be added to make failregex's more readable and maintainable. +This is also documented in the man page jail.conf (section 5). Other definitions +can be added to make failregex's more readable and maintainable to be used +through string Interpolations (see http://docs.python.org/2.7/library/configparser.html) General rules: Use "before" if you need to include a common set of rules, like syslog or if -there's a common set of regexs for multiple filters. +there is a common set of regexes for multiple filters. -Use "after" if you wish to allow the user to overwrite a set of customisation's +Use "after" if you wish to allow the user to overwrite a set of customisations of the current filter. This file doesn't need to exist. -Try to avoid using ignoreregex mainly for performance reasons. The case when -you would use it is if in trying to avoid using ignoreregex, you end up with -an unreadable failregex. +Try to avoid using ignoreregex mainly for performance reasons. The case when you +would use it is if in trying to avoid using it, you end up with an unreadable +failregex. Syslog: -If your application logs to syslog you can use the following to capture that -part. So as a base use: +If your application logs to syslog you can take advantage of log line prefix +definitions present in common.conf. So as a base use: [INCLUDES] -before = commmon.conf +before = common.conf [Definition] @@ -213,113 +221,119 @@ _daemon = app failregex = ^%(__prefix_line)s In this example common.conf defines __prefix_line which also contains the -_daemon name, (in syslog terms the service) you specified. _daemon can also be -a regex. +_daemon name (in syslog terms the service) you have just specified. _daemon +can also be a regex. -So the following uses a _daemon set to "dovecot" +For example, to capture following line _daemon should be set to "dovecot" Dec 12 11:19:11 dunnart dovecot: pop3-login: Aborted login (tried to use disabled plaintext auth): rip=190.210.136.21, lip=113.212.99.193 -So now ^%(__prefix_line)s matches "Dec 12 11:19:11 dunnart dovecot: ". Note it -matches the trailing space. Putting a space after ^%(__prefix_line)s in the -regex will probably not match. +and then ^%(__prefix_line)s would match "Dec 12 11:19:11 dunnart dovecot: +". Note it matches the trailing space(s) as well. -Substitutions: +Substitutions (AKA string interpolations): -Substation's are what the syslog uses. The regex bits of %(_name)s substitute -the _name definition into the regex. They are useful for making the regexes -more readable and also defining regex parts that occur in multiple log lines. +We have used string interpolations in above examples. They are useful for +making the regexes more readable, reuse generic patterns in multiple failregex +lines, and also to refer definition of regex parts to specific filters or even +to the user. General principle is that value of a _name variable replaces +occurrences of %(_name)s within the same section or anywhere in the config file +if defined in [DEFAULT] section. Regular Expressions: -The regular expression you will be writing will assume that the date/time has -been removed from the log line because this is how fail2ban works internally. - -If the format is like '<date...> error 1.2.3.4 is evil' then you will need to -match the < at the start so regex should be similar to '^<> <HOST> is evil$'. +Regular expressions (failregex, ignoreregex) assume that the date/time has been +removed from the log line (this is just how fail2ban works internally ATM). -Use <HOST> where the IP/domain name appears in the log line. +If the format is like '<date...> error 1.2.3.4 is evil' then you need to match +the < at the start so regex should be similar to '^<> <HOST> is evil$' using +<HOST> where the IP/domain name appears in the log line. The following general rules apply to regular expressions: -* Ensure regexs start with a ^ and are restrictive as possible. E.g. not .* if - \d+ is sufficient -* Use the functionality of regexs http://docs.python.org/2/library/re.html -* Try to make the regular expression readable (as much as possible). E.g. - (?:...) represents a non-capturing regex but (...) is more readable. - -If you only have a basic knowledge of regular repressions read -http://docs.python.org/2/library/re.html first. Really. It doesn't take long -and will remind you which bits you need to escape and which bits you don't. - -Developing/testing the regex: +* ensure regexes start with a ^ and are as restrictive as possible. E.g. do not + use .* if \d+ is sufficient; +* use functionality of Python regexes defined in the standard Python re library + http://docs.python.org/2/library/re.html; +* make regular expressions readable (as much as possible). E.g. + (?:...) represents a non-capturing regex but (...) is more readable, thus + preferred. -You can develop the regex in the file or on the command line depending on your -preference. You can also use the samples you've created in the test cases or -test them one at a time. +If you have only a basic knowledge of regular repressions we advise to read +http://docs.python.org/2/library/re.html first. It doesn't take long and would +remind you e.g. which characters you need to escape and which you don't. -The general tool is fail2ban-regex. To see how to use it run: +Developing/testing a regex: -./fail2ban-regex --help +You can develop a regex in a file or using command line depending on your +preference. You can also use samples you have already created in the test cases +or test them one at a time. -Take note of -l heavydebug / -l debug and -v as they will be most useful. +The general tool for testing Fail2Ban regexes is fail2ban-regex. To see how to +use it run: -TIP: Take a look at the source code of the application. You may see optional or - extra log messages, or parts there of, that need to form part of your regex. - It may also show how some parts are con trained and different formats - depending on configuration or less common usages. +./fail2ban-regex --help -TIP: Some applications log spaces at the end. If you're not sure add \s*$ as the - end part of the regex. +Take note of -l heavydebug / -l debug and -v as they might be very useful. -If your regex isn't matching take a look at http://www.debuggex.com/?flavor=python +TIP: Take a look at the source code of the application you are developing + failregex for. You may see optional or extra log messages, or parts there + of, that need to form part of your regex. It may also reveal how some + parts are constrained and different formats depending on configuration or + less common usages. -Using the regex from the ./fail2ban-regex output (to ensure all substitutions -are done) and with <HOST> replaced with (?&.ipv4). Set the regex type to -Python. +TIP: Some applications log spaces at the end. If you are not sure add \s*$ as + the end part of the regex. -For the test data put your log output with the time removed. +If your regex is not matching, http://www.debuggex.com/?flavor=python can help +to tune it: -When you've fixed the regex put it back into your filter file. +* use regex from the ./fail2ban-regex output (to ensure all substitutions are +done) and replace <HOST> with (?&.ipv4). Make sure that regex type set to +Python; +* for the test data put your log output with the time removed; +- when you have fixed the regex put it back into your filter file. Please spread the good word about debuggex - Serge Toarca is kindly continuing its free availability to Open Source developers. Finishing up: -If you've created a new filter, add an entry in config/jail.conf. The theory -here is that a user will create a jail.conf with [filtername]\nenable=true. +If you've added a new filter, add a new entry in config/jail.conf. The theory +here is that a user will create a jail.local with [filtername]\nenable=true to +enable your jail. So more specifically in the [filter] section in jail.conf: -* Ensure that you have "enabled = false", we want people to enable as needed -* use "filter =" set to your filter name. -* use a action to disable ports associated with the application -* set "logpath" to a usual location for the log file for the application. -* If the default findtime or bantime isn't appropriate to the filter set a value - that is more appropriate. +* ensure that you have "enabled = false" (users will enable as needed); +* use "filter =" set to your filter name; +* use a typical action to disable ports associated with the application; +* set "logpath" to the usual location of application log file; +* if the default findtime or bantime isn't appropriate to the filter, specify + more appropriate choices (possibly with a brief comment line). -Send the fail2ban a git pull request (See "Pull Requests" above) containing -your great work. +Submit github pull request (See "Pull Requests" above) for +github.com/fail2ban/fail2ban containing your great work. Filter Security --------------- Poor filter regular expressions are susceptible to DoS attacks. -When a remote user has the ability to introduce text that will match the -filter regex, such that the inserted text matches the <HOST> part, they have the +When a remote user has the ability to introduce text that would match filter's +failregex, while matching inserted text to the <HOST> part, they have the ability to deny any host they choose. -So the <HOST> part must be anchored on text generated by the application, and not -the user, to a sufficient extent that the user cannot insert the entire text. +So the <HOST> part must be anchored on text generated by the application, and +not the user, to a extent sufficient to prevent user inserting the entire text +matching this or any other failregex. -Ideally filter regex should anchor to the beginning and end of the log line -however as more applications log at the beginning than the end, anchoring the +Ideally filter regex should anchor at the beginning and at the end of log line. +However as more applications log at the beginning than the end, anchoring the beginning is more important. If the log file used by the application is shared -with other applications, like system logs, ensure the other application that -use that log file do not log user generated text at the beginning of the line, -or, if they do, ensure the regexs of the filter are sufficient to mitigate the -risk of insertion. +with other applications, like system logs, ensure the other application that use +that log file do not log user generated text at the beginning of the line, or, +if they do, ensure the regexes of the filter are sufficient to mitigate the risk +of insertion. Examples of poor filters @@ -714,11 +728,11 @@ ver. 0.8.12 (2013/XX/XXX) - wanna-be-released ----------- - Fixes: - + - New Features: - + - Enhancements: - + and adjust common/version.py to carry .dev suffix to signal a version under development. |