CAPEC-41: Using Meta-characters in E-mail Headers to Inject Malicious Payloads

Overview

CAPEC-41 (Using Meta-characters in E-mail Headers to Inject Malicious Payloads) is a detailed-level attack pattern catalogued by MITRE in the Common Attack Pattern Enumeration and Classification (CAPEC). It describes a recurring method attackers use to exploit software weaknesses.

How the attack works

The phases an attacker typically follows to carry out this attack.

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.
- 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.
Step 2
Exploit
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.
- 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.

What the attacker needs

Prerequisites

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

Skills required

Low skill: To distribute email

Consequences

What a successful CAPEC-41 attack can achieve.

Execute Unauthorized Commands

Affects: Confidentiality, Integrity, Availability

Run Arbitrary Code

How to mitigate it

Defenses that reduce the risk of CAPEC-41.

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

Examples

To: From: Header payme def: whatever

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.

The CWE weaknesses that CAPEC-41 exploits.

How this attack relates to others in the CAPEC hierarchy.

Parent

Frequently asked questions

Common questions about CAPEC-41.

What is CAPEC-41?

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.

How does a Using Meta-characters in E-mail Headers to Inject Malicious Payloads attack work?

It typically unfolds over 2 phases. It begins with: [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.

How do you prevent CAPEC-41?

Design: Perform validation on email header data

What weaknesses does CAPEC-41 target?

CAPEC-41 exploits 3 CWE weaknesses, including CWE-88 (Improper Neutralization of Argument Delimiters in a Command ('Argument Injection')), CWE-150 (Improper Neutralization of Escape, Meta, or Control Sequences), CWE-697 (Incorrect Comparison).

How severe is CAPEC-41?

MITRE rates CAPEC-41 as High severity with high likelihood of attack.

References

MITRE CAPEC definition (CAPEC-41) (opens in a new tab)

Attack-pattern data is sourced from the MITRE CAPEC catalog (v3.9). Weakness associations link to the corresponding CWE entries on RadicalNotion.AI.