CVE-2026-116265

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

Published Oct 28, 2026 CVSS 3.1 · 5.3 Medium EPSS < 1% KEV · Not listed
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.

Remediation

Vendor Solution

Upgrade to MIME-tools 5.521 or later.

Tracking

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Advisories

No advisories available
History
Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'yes', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}

Type Values Removed Values Added
Weaknesses CWE-179
References
Metrics threat_severity

None

cvssV3_1

{'score': 5.3, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N'}

threat_severity

Moderate

Type Values Removed Values Added
First Time appeared Perl
Perl mime::field::paramval
Vendors & Products Perl
Perl mime::field::paramval
Type Values Removed Values Added
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.
Title MIME::Field::ParamVal versions before 5.521 for Perl do not flag an ambiguous multipart boundary written as RFC 2231 continuations
Weaknesses CWE-436
References
Weaknesses

Sources

Status
PUBLISHED
Assigner
CPANSec
Published
Updated
Nov 5, 2026, 8:18 PM
Reserved
Oct 25, 2026, 6:05 PM
Status
Awaiting Analysis
Published
Oct 28, 2026, 6:17 PM
Modified
Nov 5, 2026, 9:18 PM
Severity
Moderate
Public date
Oct 28, 2026, 5:32 PM