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CVE-2026-116265                                      CPAN Security Group
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         CVE ID:  CVE-2026-116265

   Distribution:  MIME-tools
       Versions:  before 5.521
       MetaCPAN:  https://metacpan.org/dist/MIME-tools
       VCS Repo:  https://salsa.debian.org/dskoll/mime-tools

MIME::Field::ParamVal versions before 5.521 for Perl do not flag an
ambiguous multipart boundary written as RFC 2231 continuations

Description
-----------
MIME::Field::ParamVal versions before 5.521 for Perl do not flag an
ambiguous multipart boundary written as RFC 2231 continuations.

The boundary ambiguity checks look only at a plain boundary= parameter,
and a boundary split into RFC 2231 sections (boundary*0=, boundary*1=
and so on) is joined after they have run. A repeated section number is
concatenated rather than reported as a duplicate. From version 5.518,
an encoded word or trailing whitespace in such a boundary also goes
unflagged, although multipart_boundary() decodes or strips it.

A remote sender can make MIME::Parser split a message on a different
boundary than other mail readers, hiding an attachment from a filter
that relies on ambiguous_content() while the recipient's mail client
shows it.

Problem types
-------------
- CWE-436 Interpretation Conflict

Solutions
---------
Upgrade to MIME-tools 5.521 or later.

References
----------
https://metacpan.org/release/DSKOLL/MIME-tools-5.521/changes