[Users] [Bug 4652] New: Incorrect multi-RFC2047-encoded-word header field displayed less fault-tolerant than possible.

[noreply at thewildbeast.co.uk]

https://www.thewildbeast.co.uk/claws-mail/bugzilla/show_bug.cgi?id=4652

            Bug ID: 4652
           Summary: Incorrect multi-RFC2047-encoded-word header field
                    displayed less fault-tolerant than possible.
           Product: Claws Mail (GTK 2)
           Version: 3.19.1
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P3
         Component: Other
          Assignee: users at lists.claws-mail.org
          Reporter: claws-mail-devel at nopicturesplease.de

Occasionally I receive mails that include an incorrectly RFC2047 encoded
Subject header like:

Subject: =?utf-8?B?TmV3IFRyYWRpdGlvbmFsIENhY2hlOiBNw7xobGdhc3NlbmjD?=
 =?utf-8?B?vHR0ZSAoR0NBMFhKUiksIDguODltaSBOVyAoMTQuM2ttIE5XKQ==?=

This is incorrect as by RFC2047 5.3:
  The 'encoded-text' in an 'encoded-word' must be self-contained;
  'encoded-text' MUST NOT be continued from one 'encoded-word' to
  another.

The decoding is:

Subject: New Traditional Cache: Mühlgassenh<1st byte of 2-byte character>
 <2nd byte of 2-byte character>tte (GCA0XJR), 8.89mi NW (14.3km NW)

Claws-mail displays these Header files in an unreadble way, as it suppresses
display of some characters after the incorrect encoding.

Nonetheless, I do receive such emails and I cannot reasonably ask the sender to
prepare RFC2047 compliant emails. I would prefer claws-mail to be as
fault-tolerant as other mail readers, here.

I have spotted the cause for this behavior in src/common/unmime.c
unmime_header() which is (RFC compliant!) parsing MIME encoded headers one
encoding after the other. Changing the processing in a way to first collect and
decode all subsequent encodings, before conv'ing them into the target character
set, would make this behavior more fault-tolerant.

While preparing a patch proposal for this behavior I spotted some other
potential flaws when unmime'ing header fields, e.g. in handling of RFC822
quoted-string, for which I'll need deeper analysis before elaborating further.

I'll prepare a patch proposal for src/common/unmime.c unmime_header() and
attach it to this bug report, as soon as it seems to be ready for review.

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