Log messages of banking and e-commerce applications might include credit card numbers (Primary Account Number or PAN). According to privacy best practices and the requirements of the Payment Card Industry Data Security Standards (PCI-DSS), PAN must be rendered unreadable. The syslog-ng PE application uses a regular expression to detect credit card numbers, and provides two ways to accomplish this: you can either mask the credit card numbers, or replace them with a hash. To mask the credit card numbers, use the credit-card-mask() or the credit-card-hash() rewrite rules in a log path.
Usage
@include "scl/rewrite/cc-mask.conf"
rewrite { credit-card-mask(value("<message-field-to-process>")); };
By default, these rewrite rules process the MESSAGE part of the log message.
credit-card-hash()
| Synopsis: |
credit-card-hash(value("<message-field-to-process>")) |
Description: Process the specified message field (by default, ${MESSAGE}), and replace any credit card numbers (Primary Account Number or PAN) with its 16-character-long SHA-1 hash.
credit-card-mask()
| Synopsis: |
credit-card-mask(value("<message-field-to-process>")) |
Description: Process the specified message field (by default, ${MESSAGE}), and replace the 7-12th character of any credit card numbers (Primary Account Number or PAN) with asterisks (*). For example, syslog-ng PE replaces the number 5542043004559005 with 554204******9005.
Filters and substitution rewrite rules can use regular expressions. In regular expressions, the characters ()[].*?+^$|\ are used as special symbols. Depending on how you want to use these characters and which quotation mark you use, these characters must be used differently, as summarized below.
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Strings between single quotes ('string') are treated literally and are not interpreted at all, you do not have to escape special characters. For example, the output of '\x41' is \x41 (characters as follows: backslash, x(letter), 4(number), 1(number)). This makes writing and reading regular expressions much more simple: it is recommended to use single quotes when writing regular expressions.
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When enclosing strings between double-quotes ("string"), the string is interpreted and you have to escape special characters, that is, to precede them with a backslash (\) character if they are meant literally. For example, the output of the "\x41" is simply the letter a. Therefore special characters like \(backslash) or "(quotation mark) must be escaped (\\ and \"). The following expressions are interpreted: \a, \n, \r, \t, \v. For example, the \$40 expression matches the $40 string. Backslashes have to be escaped as well if they are meant literally, for example, the \\d expression matches the \d string.
TIP: If you use single quotes, you do not need to escape the backslash, for example, match("\\.") is equivalent to match('\.').
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Enclosing alphanumeric strings between double-quotes ("string") is not necessary, you can just omit the double-quotes. For example, when writing filters, match("sometext") and match(sometext) will both match for the sometext string.
NOTE: Only strings containing alphanumerical characters can be used without quotes or double quotes. If the string contains whitespace or any special characters (()[].*?+^$|\ or ;:#), you must use quotes or double quotes.
When using the ;:# characters, you must use quotes or double quotes, but escaping them is not required.
By default, all regular expressions are case sensitive. To disable the case sensitivity of the expression, add the flags(ignore-case) option to the regular expression.
filter demo_regexp_insensitive { host("system" flags(ignore-case)); };
The regular expressions can use up to 255 regexp matches (${1} ... ${255}), but only from the last filter and only if the flags("store-matches") flag was set for the filter. For case-insensitive searches, use the flags("ignore-case") option.
By default, syslog-ng uses PCRE-style regular expressions. To use other expression types, add the type() option after the regular expression.
The syslog-ng PE application supports the following expression types:
pcre
Description: Use Perl Compatible Regular Expressions (PCRE). Starting with syslog-ng PE version 3.1, PCRE expressions are supported on every platform. If the type() parameter is not specified, syslog-ng uses PCRE regular expressions by default.
PCRE regular expressions have the following flag options:
global
Usable only in rewrite rules: match for every occurrence of the expression, not only the first one.
ignore-case
Disable case-sensitivity.
store-matches:
Store the matches of the regular expression into the $0, ... $255 variables. The $0 stores the entire match, $1 is the first group of the match (parentheses), and so on. Named matches (also called named subpatterns), for example, (?<name>...), are stored as well. Matches from the last filter expression can be referenced in regular expressions.
unicode
Use Unicode support for UTF-8 matches: UTF-8 character sequences are handled as single characters.
utf8
An alias for the unicode flag.
Example: Using PCRE regular expressions
rewrite r_rewrite_subst
{subst("a*", "?", value("MESSAGE") flags("utf8" "global")); };
string
Description: Match the strings literally, without regular expression support. By default, only identical strings are matched. For partial matches, use the flags("prefix") or the flags("substring") flags.
glob
Description: Match the strings against a pattern containing '*' and '?' wildcards, without regular expression and character range support. The advantage of glob patterns to regular expressions is that globs can be processed much faster.
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* matches an arbitrary string, including an empty string
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? matches an arbitrary character
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The wildcards can match the / character.
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You cannot use the * and ? literally in the pattern.
The host(), match(), and program() filter functions and some other syslog-ng objects accept regular expressions as parameters. But evaluating general regular expressions puts a high load on the CPU, which can cause problems when the message traffic is very high. Often the regular expression can be replaced with simple filter functions and logical operators. Using simple filters and logical operators, the same effect can be achieved at a much lower CPU load.
Example: Optimizing regular expressions in filters
Suppose you need a filter that matches the following error message logged by the xntpd NTP daemon:
xntpd[1567]: time error -1159.777379 is too large (set clock manually);
The following filter uses regular expressions and matches every instance and variant of this message.
filter f_demo_regexp {
program("demo_program") and
match("time error .* is too large .* set clock manually"); };
Segmenting the match() part of this filter into separate match() functions greatly improves the performance of the filter.
filter f_demo_optimized_regexp {
program("demo_program") and
match("time error") and
match("is too large") and
match("set clock manually"); };
