Vulnerability · Published Oct 28, 2026 · Assigned by CPANSec
CVE-2026-116265MIME::Field::ParamVal versions before 5.521 for Perl do not flag an ambiguous multipart boundary written as RFC 2231 continuations
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::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 packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:12 | libmime-tools-perl | no fix listed | DEBIAN-CVE-2026-116265 |
| Debian:13 | libmime-tools-perl | no fix listed | DEBIAN-CVE-2026-116265 |
| Debian:14 | libmime-tools-perl | 5.522-1 | DEBIAN-CVE-2026-116265 |
| Ubuntu:22.04:LTS | libmime-tools-perl | no fix listed | UBUNTU-CVE-2026-116265 |
| Ubuntu:24.04:LTS | libmime-tools-perl | no fix listed | UBUNTU-CVE-2026-116265 |
| Ubuntu:26.04:LTS | libmime-tools-perl | no fix listed | UBUNTU-CVE-2026-116265 |
| Ubuntu:26.10 | libmime-tools-perl | no fix listed | UBUNTU-CVE-2026-116265 |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| MIME-tools | 0 – 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