---
id: "CVE-2026-116272"
kind: "vulnerability"
aliases: ["CVE-2026-116272"]
title: "Perl MIME::Field::ParamVal: duplicate boundary check lets mail hide attachments"
severity: "medium"
cvss: null
epss: null
exploited: false
status: "open"
category: "package"
products: []
ecosystems: []
tags: ["mail-filtering", "mime-parser", "package", "perl"]
not_affected_if: ["no-ambiguous-content-filter", "no-mime-parser"]
published_at: "2026-10-28T18:17:13+00:00"
first_seen_at: "2026-10-28T18:34:33+00:00"
updated_at: "2026-10-28T18:35:23+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-116272", "first_seen_at": "2026-10-28T18:34:33+00:00"}]
---

# Perl MIME::Field::ParamVal: duplicate boundary check lets mail hide attachments

MIME::Field::ParamVal in Perl versions before 5.521 fails to detect a duplicate boundary parameter when its name contains a nested comment, so the parser stores it under a different literal name. A remote sender can use this mismatch to hide an attachment from a filter that relies on ambiguous_content() while the recipient's mail client still shows it.

_Summary, check and fix written by a model from the sources; labelled as such._

## How to check

- Check the installed MIME::Field::ParamVal version with `perl -MMIME::Field::ParamVal -e 'print $MIME::Field::ParamVal::VERSION'` (unknown whether the sources give a different command)
- Check whether any mail filter code calls `ambiguous_content()` from MIME::Parser

## Fix

- Upgrade MIME::Field::ParamVal to `5.521` or later

## Timeline

- 2026-10-28T18:34:33+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-116272

## From the sources

MIME::Field::ParamVal versions before 5.521 for Perl do not flag a duplicate boundary parameter whose name contains a nested comment.

A parameter written boundary((c))="A" or boundary(\))="A" is stored under that literal name rather than as boundary. A second boundary parameter is then not reported as a duplicate, and MIME::Parser splits the message on it.

Readers that skip comments as RFC 5322 allows take the first boundary instead. A remote sender can hide an attachment from a filter that relies on ambiguous_content() while the recipient's mail client shows it.

---

_Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_