CVE Catalog

CVE-2026-116266

MediumCVSS 5.3
Published: Updated: Translated: NVD NIST

Exploitation Probability (EPSS)

Low risk
0.21%

11th percentile - higher than 11% of all known CVEs

Summary

MIME::Head versions from 5.518 before 5.521 for Perl decode a partly encoded multipart boundary without flagging the parse as ambiguous. The multipart_boundary() method decodes RFC 2047 encoded words anywhere in the boundary, but the ambiguity check only fires when the whole value is one encoded word. A boundary such as abc=?us-ascii?Q?def?= is used as abcdef, and ambiguous_content() returns false.

Risk Assessment

A remote sender can hide an attachment from a filter relying on ambiguous_content() while the recipient's mail client shows it, since other readers split the message on the literal value. This may lead to delivery of a malicious attachment to the recipient.

Recommendation

Update MIME::Head to version 5.521 or later. Do not rely solely on ambiguous_content() in mail security filters — apply additional attachment verification layers.

Related vulnerabilities

Original NVD description (English source)

MIME::Head versions from 5.518 before 5.521 for Perl decode a partly encoded multipart boundary without flagging the parse as ambiguous. The multipart_boundary() method decodes RFC 2047 encoded words anywhere in the boundary, but the ambiguity check only fires when the whole value is one encoded word. A boundary such as abc=?us-ascii?Q?def?= is used as abcdef, and ambiguous_content() returns false. Encoded words are not allowed in parameters, so other mail readers split the message on the literal value. A remote sender can hide an attachment from a filter that relies on ambiguous_content() while the recipient's mail client shows it.

Vulnerability data from NVD (NIST) · CISA KEV · EPSS