[Users] [Bug 4548] New: Regular expression with escaped opening bracket incorrectly parsed

[noreply at thewildbeast.co.uk]

https://www.thewildbeast.co.uk/claws-mail/bugzilla/show_bug.cgi?id=4548

            Bug ID: 4548
           Summary: Regular expression with escaped opening bracket
                    incorrectly parsed
           Product: Claws Mail (GTK 2)
           Version: 3.17.8
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P3
         Component: Filtering
          Assignee: users at lists.claws-mail.org
          Reporter: thewildbeast.reg at kjpetrie.co.uk

The following filter log extract sums it up well:

[2021-11-14 10:39:10] header value [ from evenas.org (localhost [127.0.0.1]) by
evenas.org (8.16.1/8.16.1) with ESMTP id 1AE339TH023255 for <root at evenas.org>;
Sun, 14 Nov 2021 03:03:09 GMT (envelope-from root at evenas.org) ] does NOT match
regular expression [ \[41\.25[2-5]\. ] (Case insensitive)
[2021-11-14 10:39:10] header value [ from evenas.org (localhost [127.0.0.1]) by
evenas.org (8.16.1/8.16.1) with ESMTP id 1AE339TH023255 for <root at evenas.org>;
Sun, 14 Nov 2021 03:03:09 GMT (envelope-from root at evenas.org) ] does NOT
contain [ [46.105 ] (Case insensitive)
[2021-11-14 10:39:10] header value [ from evenas.org (localhost [127.0.0.1]) by
evenas.org (8.16.1/8.16.1) with ESMTP id 1AE339TH023255 for <root at evenas.org>;
Sun, 14 Nov 2021 03:03:09 GMT (envelope-from root at evenas.org) ] matches regular
expression [ \[51\.(178)|(25[4,5]) ] (Case insensitive)
> message matches
[2021-11-14 10:39:10] applying action [ move "#mh/Local Folders/trash" ]

The opening "\[" should be interpreted as a literal "[", anchoring the RE to
substrings beginning with that character, in this context to IP addresses. It
is most definitely not the beginning of a bracket expression. The RE should
only match "[51." followed by "178", "254" or "255". There is no "[51." in the
header, so it should not match. It can only match if the opening "\" is ignored
and the "[" is then used to open a bracketed expression matching a
"5","1","\",".","(","7","8",")","|","2", or "4" followed by a ")". That would
then match the "1)" at the end of "(8.16.1/8.16.1)". This is clearly not
intended.

Steps to reproduce:

1. Create an e-mail containing the header "Received: from evenas.org (localhost
[127.0.0.1]) by evenas.org (8.16.1/8.16.1) with ESMTP id 1AE339TH023255 for
<root at evenas.org>; Sun, 14 Nov 2021 03:03:09 GMT (envelope-from
root at evenas.org)" and place it in a folder in a Claws Mail account.

2. Create a filter rule for a Received header to match "\[51\.(178)|(25[4,5])"
as a regular expression, with a non-destructive action.

3. Enable filter logging and set the logging level to high.

4. Select the message and filter selected.

5. View the log.

Result:

The message matches the filter condition.

Expected Result:

The message should not match.

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