Home > CAPEC List > CAPEC-41: Using Meta-characters in E-mail Headers to Inject Malicious Payloads (Version 2.11)  

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

Using Meta-characters in E-mail Headers to Inject Malicious Payloads
Definition in a New Window Definition in a New Window
Attack Pattern ID: 41
Abstraction: Detailed
Status: Draft
Completeness: Complete
Presentation Filter:
+ Summary

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.

+ Attack Steps
  1. 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.

  1. 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.

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

+ Typical Severity


+ Typical Likelihood of Exploit

Likelihood: High

+ Methods of Attack
  • Injection
  • API Abuse
+ Examples-Instances


Header<SCRIPT>payme</SCRIPT>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.

+ Attacker Skills or Knowledge Required

Skill or Knowledge Level: Low

To distribute email

+ Solutions and Mitigations

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

+ Attack Motivation-Consequences
ScopeTechnical ImpactNote
Execute unauthorized code or commands
Run Arbitrary Code
+ Injection Vector


+ Payload


+ Activation Zone

Email processing routines of Email program

+ Payload Activation Impact

Enables attacker to execute server side code with any commands that the program owner has privileges to.

+ Purposes
  • Penetration
+ CIA Impact
Confidentiality Impact: HighIntegrity Impact: HighAvailability Impact: High
+ Technical Context
Architectural Paradigms
+ References
[R.41.1] [REF-2] G. Hoglund and G. McGraw. "Exploiting Software: How to Break Code". Addison-Wesley. February 2004.
+ Content History
CAPEC Content TeamThe MITRE Corporation2014-06-23Internal_CAPEC_Team

More information is available — Please select a different filter.
Page Last Updated or Reviewed: August 04, 2017