Filter out passwords with mutate

Elastic Stack Logstash
1

Hi,

I'm trying to filter out passwords that icingabeat sends out.
The field with password is "check_result.command" and the password is always after "-p," or "-P,".

Example line:
/usr/lib/nagios/plugins/check_mysql, -H, hostname.tld, -p, Xkaw*!dH=VlM@, -u, monitoring

(the password is an example).

I've tried:

filter {
if "icingabeat" in [src_type] {
if [check_result][command] =~ /.*-[pP],.*/ {
mutate {
gsub => [
"[check_result][command]", "-p, [^,]*", "-p, FILTERED_PASSWORD"
]
}
}
}
}

Thou it does not catch the password-field. Any ideas?

2

tl;dr: the .* at the beginning of your outer if-statement pattern is too greedy; it captures the whole string (including any -p, sequence) up until a newline, so the next character sequence will never be a literal hyphen (-).

Your outer check pattern should be / -[pP], / (note the literal spaces on either side and absence of other patterns).

While attempting to come up with a solution, I improved your pattern a bit, and got to a point where I could reliably capture passwords without changing the case of the preceding p/P (not sure if this matters for you):

(?<= -[pP], )[^,]*

In the pipeline config, this becomes:

filter {
  mutate {
    gsub => ["[check_result][command]", "(?<= -[pP], )[^,]*", "FILTERED_PASSWORD"]
  }
}

By using a positive lookbehind assertion of -[pP],, we can capture sequences that are proceeded by this pattern without including it in our match, and since the -p, or -P, isn't part of the match, we don't have to worry about replacing it.

Which brings me to: EDGE CASES

What if a password includes a literal comma? Will this end up leaking everything after that literal comma into your logs? :weary:

If your producer handles literal commas in passwords by escaping them (e.g., by prefixing them with a backslash), the following would ensure we capture the whole password):

(?<= -[pP], )(?:\\,|[^,])*

In our repeated match, we either capture a literal-backslash-literal-comma sequence, or anything-but-a-comma.

If your producer does not escape literal commas, the following pattern would be a bit better, as it only breaks the capture once it encounters either a literal-comma-literal-space sequence or EOL by moving the break pattern into a positive-lookahead clause and making the repeat operator less greedy:

(?<= -[pP], ).+?(?=, |$)

I tested the above pattern with the following command lines, and it seems to handle the edge-cases well.

/usr/lib/nagios/plugins/check_mysql, -H, hostname.tld, -p, Xkaw*!dH=VlM@, -u, monitoring
/usr/lib/nagios/plugins/check_mysql, -H, hostname.tld, -p, Xkaw*!d,H=VlM@, -u, monitoring
/usr/lib/nagios/plugins/check_mysql, -H, hostname.tld, -p, Xkaw*!dH=V,lM@, -u, monitoring
/usr/lib/nagios/plugins/check_mysql, -H, hostname.tld, -u monitoring -p, Xkaw*!dH=V,lM@
/usr/lib/nagios/plugins/check_mysql, -H, hostname.tld, -u monitoring -p, Xkaw*!dH=VlM@
/usr/lib/nagios/plugins/check_mysql, -H, hostname.tld, -u monitoring -p, ,Xkaw*!dH=VlM@
/usr/lib/nagios/plugins/check_mysql, -H, hostname.tld, -u monitoring -p, Xkaw*!dH=VlM@,
/usr/lib/nagios/plugins/check_mysql, -H, hostname.tld, -P, Xkaw*!dH=VlM@, -u, monitoring
/usr/lib/nagios/plugins/check_mysql, -H, hostname.tld, -P, Xkaw*!d,H=VlM@, -u, monitoring
/usr/lib/nagios/plugins/check_mysql, -H, hostname.tld, -P, Xkaw*!dH=V,lM@, -u, monitoring
/usr/lib/nagios/plugins/check_mysql, -H, hostname.tld, -u monitoring -P, Xkaw*!dH=V,lM@
/usr/lib/nagios/plugins/check_mysql, -H, hostname.tld, -u monitoring -P, Xkaw*!dH=VlM@
/usr/lib/nagios/plugins/check_mysql, -H, hostname.tld, -u monitoring -P, ,Xkaw*!dH=VlM@
/usr/lib/nagios/plugins/check_mysql, -H, hostname.tld, -u monitoring -P, Xkaw*!dH=VlM@,
3

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