COMMON ATTACK PATTERN ENUMERATION AND CLASSIFICATIONLive MITRE record

CAPEC-41

Using Meta-characters in E-mail Headers to Inject Malicious Payloads

This type of attack involves an attacker leveraging meta-characters in email headers to inject improper behavior into email programs. Email software has become increasingly sophisticated and feature-rich. In addition, email applications are ubiquitous and connected directly to the Web making them ideal targets to launch and propagate attacks. As the user demand for new functionality in email applications grows, they become more like browsers with complex rendering and plug in routines. As more email functionality is included and abstracted from the user, this creates opportunities for attackers. Virtually all email applications do not list email header information by default, however the email header contains valuable attacker vectors for the attacker to exploit particularly if the behavior of the email client application is known. Meta-characters are hidden from the user, but can contain scripts, enumerations, probes, and other attacks against the user's system.

Abstraction

Detailed

Typical severity

High

Likelihood of attack

High

Understand the attack

What is this attack pattern?

This type of attack involves an attacker leveraging meta-characters in email headers to inject improper behavior into email programs. Email software has become increasingly sophisticated and feature-rich. In addition, email applications are ubiquitous and connected directly to the Web making them ideal targets to launch and propagate attacks. As the user demand for new functionality in email applications grows, they become more like browsers with complex rendering and plug in routines. As more email functionality is included and abstracted from the user, this creates opportunities for attackers. Virtually all email applications do not list email header information by default, however the email header contains valuable attacker vectors for the attacker to exploit particularly if the behavior of the email client application is known. Meta-characters are hidden from the user, but can contain scripts, enumerations, probes, and other attacks against the user's system.

Execution flow

How does the attack proceed, step by step?

1

Experiment

Identify and characterize metacharacter-processing vulnerabilities in email headers

An attacker creates emails with headers containing various metacharacter-based malicious payloads in order to determine whether the target application processes the malicious content and in what manner it does so.

Techniques used

  • Use an automated tool (fuzzer) to create malicious emails headers containing metacharacter-based payloads.
  • Manually tampering email headers to inject malicious metacharacter-based payload content in them.
2

Exploit

Attack step

An attacker leverages vulnerabilities identified during the Experiment Phase to inject malicious email headers and cause the targeted email application to exhibit behavior outside of its expected constraints. Techniques Send emails with specifically-constructed, metacharacter-based malicious payloads in the email headers to targeted systems running email processing applications identified as vulnerable during the Experiment Phase.

Techniques used

  • Send emails with specifically-constructed, metacharacter-based malicious payloads in the email headers to targeted systems running email processing applications identified as vulnerable during the Experiment Phase.

Requirements

What does the attack require?

Prerequisites

  • This attack targets most widely deployed feature rich email applications, including web based email programs.

Skills required

  • Low: To distribute email

Resources required

Not stated in the MITRE record.

Impact

What does a successful attack lead to?

Execute Unauthorized Commands

Affected scopes: Confidentiality, Integrity, Availability

Defence

How is it prevented and mitigated?

1
Design: Perform validation on email header data
2
Implementation: Implement email filtering solutions on mail server or on MTA, relay server.
3
Implementation: Mail servers that perform strict validation may catch these attacks, because metacharacters are not allowed in many header variables such as dns names

Real world

MITRE example instances

Example instance 1Detail
To:<someone@example.com> From:<badguy@example.com> Header<SCRIPT>payme</SCRIPT>def: whatever
Example instance 2Detail
Meta-characters are among the most valuable tools attackers have to deceive users into taking some action on their behalf. E-mail is perhaps the most efficient and cost effective attack distribution tool available, this has led to the phishing pandemic. Meta-characters like \w \s \d ^ can allow the attacker to escape out of the expected behavior to execute additional commands. Escaping out the process (such as email client) lets the attacker run arbitrary code in the user's process.
CAPEC-41: Using Meta-characters in E-mail Headers to Inject Malicious Payloads — DayBreach Saldırı Sözlüğü · DayBreach