CVE-2026-116266 MIME::Head versions from 5.518 before 5.521 for Perl decode a partly encoded multipart boundary without flagging the parse as ambiguous.
- Exploited in the wild
- Not known
- Fix
- None listed
What is CVE-2026-116266?
CVE-2026-116266 is a vulnerability, published on 28 Oct 2026.
Official description
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.
Weakness: CWE-436
Which versions are affected by CVE-2026-116266?
How do I fix CVE-2026-116266?
No fix has been published for CVE-2026-116266 yet. Limit exposure of the affected software until one is available.
Is CVE-2026-116266 being exploited?
There is no known exploitation of CVE-2026-116266 in the wild and no public exploit code.
Sources
Also known as DEBIAN-CVE-2026-116266, GHSA-c5m8-q98x-42wx, UBUNTU-CVE-2026-116266.