CVE-2026-116265: vulnerability in MIME-tools
MIME::Field::ParamVal versions before 5.521 for Perl do not flag an ambiguous multipart boundary written as RFC 2231 continuations
Published
E-mail alert when it lands in KEV, gets a public PoC or its score goes up.
3Vexday Risk Score
No sign of exploitation. No public exploitation artifact known so far.
ssvc Trackepss 0.2%
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.
Affected products
MIME-toolsRelated CVEs — MIME-tools
In the same product, most dangerous first.
CVE-2026-116271—MIME::Parser::FileUnder versions before 5.521 for Perl reuse a pre-created output directory and follow symlinks in it, letting local users redirect attachment writesEPSS 0.2%CVE-2026-116273—MIME::Parser versions before 5.521 for Perl set no limit on the number of message parts by default, allowing memory exhaustionEPSS 0.2%CVE-2026-116272—MIME::Field::ParamVal versions before 5.521 for Perl do not flag a duplicate boundary parameter whose name contains a nested commentEPSS 0.2%CVE-2026-116270—MIME::Words versions before 5.521 for Perl allow memory exhaustion via repeated "=?" sequences in decode_mimewordsEPSS 0.2%CVE-2026-116269—MIME::Field::ParamVal versions before 5.521 for Perl turn an RFC 2231 filename with a hyphenated language tag into an empty recommended filenameEPSS 0.2%CVE-2026-116268—MIME::Field::ParamVal versions before 5.521 for Perl allow CPU exhaustion via unclosed comments in header parametersEPSS 0.2%