[New-bugs-announce] [issue31449] Potential DoS Attack when Parsing Email with Huge Number of MIME Parts

[Christian Koßmann]

New submission from Christian Koßmann:

Python's email parser consumes a lot of resources (CPU and memory) when parsing emails with a large amount of MIME parts. Attackers can probably exploit this behavior to perform denial-of-service (DoS) attacks.

A potentially malicious email has the following structure:

=============================================
From: sender at example.com
To: recipient at example.com
Subject: Mutlipart DoS Attack
MIME-Version: 1.0
Content-Type: multipart/mixed; boundary="n"

This is a multi-part message in MIME format.
--n

b

--n

... a lot of parts here...

--n

b

--n--
=============================================

On my machine parsing an email with 1 million MIME parts takes around 20 seconds and with 10 million MIME parts over 3 minutes.

In my opinion, the number of MIME parts should be limited to some reasonable value to mitigate this kind of attack. The bug report contains a Python script with a proof-of-concept.

----------
components: email
files: multipart-dos-attack.py
messages: 302060
nosy: barry, ckossmann, r.david.murray
priority: normal
severity: normal
status: open
title: Potential DoS Attack when Parsing Email with Huge Number of MIME Parts
type: security
versions: Python 3.5, Python 3.6
Added file: https://bugs.python.org/file47138/multipart-dos-attack.py

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue31449>
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