# CVE-2026-116266: libmime-tools-perl: MIME::Head versions from 5.518 before 5.521 for Perl decode a partly encoded multipart boundary without flagging the...

CVE-2026-116266 is fixed in 2 products on 1 platform, first by DEBIAN-CVE-2026-116266, released November 3, 2026. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2026-116266
- Priority: Routine
- CVSS: 5.3 (medium)
- EPSS: 0.0021
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Oct 22, 2026

## 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.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | libmime-tools-perl Debian 14 | 5.522-1 | [DEBIAN-CVE-2026-116266](https://patchblox.com/security/data/fix/linux/debian-cve-2026-116266.md) | Nov 3, 2026 |
| Linux | perl-MIME-tools Fedora 43 | 5.522-1.fc43 | [FEDORA-2026-A415B3BF48](https://patchblox.com/security/data/fix/linux/fedora-2026-a415b3bf48.md) | Nov 7, 2026 |
| Linux | perl-MIME-tools opensuse-leap 16.0 | 5.522.0-bp160.1.1 | [OPENSUSE-SU-2026:22226-1](https://patchblox.com/security/data/fix/linux/opensuse-su-2026-22226-1.md) | Nov 7, 2026 |

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Data as of 2026-11-09T07:25:28Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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