---
id: "CVE-2026-116264"
kind: "vulnerability"
aliases: ["CVE-2026-116264"]
title: "Perl MIME::Parser: invalid Content-Type parameter hides multipart boundary from filters"
severity: "low"
cvss: null
epss: null
exploited: false
status: "open"
category: "package"
products: []
ecosystems: []
tags: ["mail-filtering", "mime-parser", "package", "perl"]
not_affected_if: ["no-perl-mail-filter", "versions-5.521-or-later"]
published_at: "2026-10-28T18:17:12+00:00"
first_seen_at: "2026-10-28T18:34:33+00:00"
updated_at: "2026-10-28T18:35:32+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-116264", "first_seen_at": "2026-10-28T18:34:33+00:00"}]
---

# Perl MIME::Parser: invalid Content-Type parameter hides multipart boundary from filters

MIME::Field::ParamVal before 5.521 stops parsing Content-Type parameters at the first unreadable name, dropping the multipart boundary when it comes after. MIME::Parser then keeps the body as one undecoded part without flagging ambiguity, so a message can carry an attachment that a filter relying on ambiguous_content() does not see.

_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'`
- Look for code that calls `ambiguous_content()` on MIME::Parser results to decide whether to scan or block mail

## Fix

- Upgrade MIME::Field::ParamVal to `5.521` or later
- Until upgraded, treat mail with undecoded multipart bodies as suspicious in filters that depend on ambiguous_content()

## Timeline

- 2026-10-28T18:34:33+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-116264

## From the sources

MIME::Field::ParamVal versions before 5.521 for Perl allow one invalid Content-Type parameter to hide the parameters after it, including the multipart boundary.

Parameter parsing stops at the first parameter whose name it cannot read, such as x:y=1 or a name containing an 8-bit byte, and drops every parameter after it. When the boundary is among them, MIME::Parser keeps the multipart body as a single undecoded part without marking the parse as ambiguous.

Mail readers that skip the invalid parameter still find the boundary. A remote sender can hide an attachment from a filter that relies on ambiguous_content() while the recipient's mail client shows it.

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