Vulnerability · Published Oct 28, 2026 · Assigned by CPANSec
CVE-2026-116266MIME::Head versions from 5.518 before 5.521 for Perl decode a partly encoded multipart boundary without flagging the parse as ambiguous
Medium 5.3
In plain English
A medium-severity security flaw in MIME-tools. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.2% (higher than 11% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
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.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:12 | libmime-tools-perl | no fix listed | DEBIAN-CVE-2026-116266 |
| Debian:13 | libmime-tools-perl | no fix listed | DEBIAN-CVE-2026-116266 |
| Debian:14 | libmime-tools-perl | 5.522-1 | DEBIAN-CVE-2026-116266 |
| Ubuntu:22.04:LTS | libmime-tools-perl | no fix listed | UBUNTU-CVE-2026-116266 |
| Ubuntu:24.04:LTS | libmime-tools-perl | no fix listed | UBUNTU-CVE-2026-116266 |
| Ubuntu:26.04:LTS | libmime-tools-perl | no fix listed | UBUNTU-CVE-2026-116266 |
| Ubuntu:26.10 | libmime-tools-perl | no fix listed | UBUNTU-CVE-2026-116266 |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| MIME-tools | 5.518 – before 5.521 |
Weakness: CWE-436 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N