Regex catch bad octet in IP

Question

Hi can someone explain me why last octet of the IP if 01 or 001 is not capched by this regex?

(\.?)([2-9][5-9][6-9]|[3-9][0-9][0-9]|0[0-9][0-9]?)($|\.)

Debuggex Demo

as example of the code

badOctedIPv4 := "(\\.?)([2-9][5-9][6-9]|[3-9][0-9][0-9]|0[0-9][0-9]?)($|\\.)"
ipv4Format := badOctedIPv4
matchMe := regexp.MustCompile(ipv4Format)
return matchMe.FindString(input)

the input data looks like:

10.185.248.71 - - [09/Jan/2015:19:12:06 +0000] 808840 "GET /inventoryService/inventory/purchaseItem?userId=20253471&itemId=23434300 HTTP/1.1" 500 17 "-" "Apache-HttpClient/4.2.6 (java 1.5)"
[Thu Mar 13 19:04:13 2014] [error] [client 50.0.134.125] File does not exist: /var/www/favicon.ico
192.168.000.254 - - [13/Sep/2006:07:01:51 -0700] "PROPFIND /svn/[xxxx]/[xxxx]/trunk HTTP/1.1" 401 587 10 bad
092.168.000.254 - - [13/Sep/2006:07:01:51 -0700] "PROPFIND /svn/[xxxx]/[xxxx]/trunk HTTP/1.1" 401 587 9 bad
123.234.345.001 - - [13/Sep/2006:07:01:51 -0700] "PROPFIND /svn/[xxxx]/[xxxx]/trunk HTTP/1.1" 401 587 8 bad
123.234.145.001 - - [13/Sep/2006:07:01:51 -0700] "PROPFIND /svn/[xxxx]/[xxxx]/trunk HTTP/1.1" 401 587 7 bad
345.234.123.1 - - [13/Sep/2006:07:01:51 -0700] "PROPFIND /svn/[xxxx]/[xxxx]/trunk HTTP/1.1" 401 587 6 bad
092.168.72.177 - - [22/Dec/2002:23:32:14 -0400] "GET /favicon.ico HTTP/1.1" 404 1997 www.yahoo.com "-" "Mozilla/5.0 (Windows; U; Windows NT 5.1; rv:1.7.3)..." "-" 5 bad
123.234.145.001 - - 4 bad
123.234.145.01 - - 3 bad
123.234.05.100 - - 2 bad
123.234.005.100 - - 1 bad
123.234.5.100 - - Last entry

the results returned by above code only finds all bad IP octets except the last one 001 or 01

Output of the program:

❯ go run ./findInvalidIPv4.go logfile.log
[192.168.000.254] : [.000.] : 192.168.000.254 - - [13/Sep/2006:07:01:51 -0700] "PROPFIND /svn/[xxxx]/[xxxx]/trunk HTTP/1.1" 401 587 10 bad
[092.168.000.254] : [ 092.] : 092.168.000.254 - - [13/Sep/2006:07:01:51 -0700] "PROPFIND /svn/[xxxx]/[xxxx]/trunk HTTP/1.1" 401 587 9 bad
[123.234.345.001] : [.345.] : 123.234.345.001 - - [13/Sep/2006:07:01:51 -0700] "PROPFIND /svn/[xxxx]/[xxxx]/trunk HTTP/1.1" 401 587 8 bad
[  345.234.123.1] : [ 345.] : 345.234.123.1 - - [13/Sep/2006:07:01:51 -0700] "PROPFIND /svn/[xxxx]/[xxxx]/trunk HTTP/1.1" 401 587 6 bad
[ 092.168.72.177] : [ 092.] : 092.168.72.177 - - [22/Dec/2002:23:32:14 -0400] "GET /favicon.ico HTTP/1.1" 404 1997 www.yahoo.com "-" "Mozilla/5.0 (Windows; U; Windows NT 5.1; rv:1.7.3)..." "-" 5 bad
[ 123.234.05.100] : [ .05.] : 123.234.05.100 - - 2 bad
[123.234.005.100] : [.005.] : 123.234.005.100 - - 1 bad

Output explained:

• first column [...] its the full bad IP where bad octet been found
• second column [...] its the bad octet... first match is enough
• third column is the full line passed to above func

Can some one point me what I am missing and why the 001 at the end is not matching the pattern?

Thanks

Answer 1

Your group 3 at the end:

($|\.)

Insists on either a dot or end-of-line character appearing after the last octet. That's fine for the first three octets that are guaranteed to have a . proceed it. But it won't work for the last one.

The simple fix is to just remove it or make it optional:

(\.?)([2-9][5-9][6-9]|[3-9][0-9][0-9]|0[0-9][0-9]?)($|\.?)

Add a whitespace for group 3:

(\.?)([2-9][5-9][6-9]|[3-9][0-9][0-9]|0[0-9][0-9]?)(\s|$|\.)

Or just remove it:

(\.?)([2-9][5-9][6-9]|[3-9][0-9][0-9]|0[0-9][0-9]?)

All of these have issues. So maybe this is what you really want is to match any of your 3 digit sequence with either a leading dot or a trailing dot.

\.[2-9][5-9][6-9]|\.[3-9][0-9][0-9]|\.0[0-9][0-9]|\[2-9][5-9][6-9]\.|[3-9][0-9][0-9]\.|0[0-9][0-9]\.

We start to get into regular expressions being "Write once read never again" territory.

Answer 2

@selbie thanks again for your help seems with all suggestions here i am getting closer to solve this, this regex (\.|^)([2-9][5-9][6-9]|[3-9][0-9][0-9]|0[0-9]+) seems its catching for me almost all what needed

[  192.168.2.001] : [ .001] : 192.168.2.001 - - [28/Jul/2006:10:27:10 -0300] "GET /cgi-bin/try/ HTTP/1.0" 200 3395
[192.168.000.254] : [ .000] : 192.168.000.254 - - [13/Sep/2006:07:01:51 -0700] "PROPFIND /svn/[xxxx]/[xxxx]/trunk HTTP/1.1" 401 587 10 bad
[092.168.000.254] : [  092] : 092.168.000.254 - - [13/Sep/2006:07:01:51 -0700] "PROPFIND /svn/[xxxx]/[xxxx]/trunk HTTP/1.1" 401 587 9 bad
[123.234.345.001] : [ .345] : 123.234.345.001 - - [13/Sep/2006:07:01:51 -0700] "PROPFIND /svn/[xxxx]/[xxxx]/trunk HTTP/1.1" 401 587 8 bad
[123.234.145.001] : [ .001] : 123.234.145.001 - - [13/Sep/2006:07:01:51 -0700] "PROPFIND /svn/[xxxx]/[xxxx]/trunk HTTP/1.1" 401 587 7 bad
[  345.234.123.1] : [  345] : 345.234.123.1 - - [13/Sep/2006:07:01:51 -0700] "PROPFIND /svn/[xxxx]/[xxxx]/trunk HTTP/1.1" 401 587 6 bad
[  300.234.123.1] : [  300] : 300.234.123.1 - - [13/Sep/2006:07:01:51 -0700] "PROPFIND /svn/[xxxx]/[xxxx]/trunk HTTP/1.1" 401 587 6 bad
[300.300.300.300] : [  300] : 300.300.300.300 - - [13/Sep/2006:07:01:51 -0700] "PROPFIND /svn/[xxxx]/[xxxx]/trunk HTTP/1.1" 401 587 6 bad
[ 092.168.72.177] : [  092] : 092.168.72.177 - - [22/Dec/2002:23:32:14 -0400] "GET /favicon.ico HTTP/1.1" 404 1997 www.yahoo.com "-" "Mozilla/5.0 (Windows; U; Windows NT 5.1; rv:1.7.3)..." "-" 5 bad
[123.234.145.001] : [ .001] : 123.234.145.001 - - 4 bad
[ 123.234.145.01] : [  .01] : 123.234.145.01 - - 3 bad
[ 123.234.05.100] : [  .05] : 123.234.05.100 - - 2 bad
[123.234.005.100] : [ .005] : 123.234.005.100 - - 1 bad

and its skipping the good IP like 200.200.200.200 or 100.100.100.100 so we are getting closer to get that pattern working the only case now when i see is messed is when i have time string, 02:49:12 which starts the string 02 and so on as example:

[      127.0.0.1] : [   02] : 02:49:12 127.0.0.1 GET / 200
[      127.0.0.1] : [   02] : 02:49:35 127.0.0.1 GET /index.html 200
[      127.0.0.1] : [   03] : 03:01:06 127.0.0.1 GET /images/sponsered.gif 304
[      127.0.0.1] : [   03] : 03:52:36 127.0.0.1 GET /search.php 200
[      127.0.0.1] : [   04] : 04:17:03 127.0.0.1 GET /admin/style.css 200
[      127.0.0.1] : [   05] : 05:04:54 127.0.0.1 GET /favicon.ico 404
[      127.0.0.1] : [   05] : 05:38:07 127.0.0.1 GET /js/ads.js 200

so i am still looking for an answer what i am missing in that regular expression

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edit ok this seems to do the work and its able to find the bad ip octet (\.|^)([2-9][5-9][6-9]|[3-9][0-9][0-9]|0[0-9]+)([^:/-]) added the lat 3rd group ([^:/-]) to exclude any time format with two digits