Home > CAPEC List > CAPEC-41: Using Meta-characters in E-mail Headers to Inject Malicious Payloads (Version 3.4)  

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

Attack Pattern ID: 41
Abstraction: Detailed
Status: Draft
Presentation Filter:
+ Description
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.
+ Likelihood Of Attack


+ Typical Severity


+ Relationships
Section HelpThis table shows the other attack patterns and high level categories that are related to this attack pattern. These relationships are defined as ChildOf and ParentOf, and give insight to similar items that may exist at higher and lower levels of abstraction. In addition, relationships such as CanFollow, PeerOf, and CanAlsoBe are defined to show similar attack patterns that the user may want to explore.
ChildOfStandard Attack PatternStandard Attack Pattern - A standard level attack pattern in CAPEC is focused on a specific methodology or technique used in an attack. It is often seen as a singular piece of a fully executed attack. A standard attack pattern is meant to provide sufficient details to understand the specific technique and how it attempts to accomplish a desired goal. A standard level attack pattern is a specific type of a more abstract meta level attack pattern.134Email Injection
ChildOfMeta Attack PatternMeta Attack Pattern - A meta level attack pattern in CAPEC is a decidedly abstract characterization of a specific methodology or technique used in an attack. A meta attack pattern is often void of a specific technology or implementation and is meant to provide an understanding of a high level approach. A meta level attack pattern is a generalization of related group of standard level attack patterns. Meta level attack patterns are particularly useful for architecture and design level threat modeling exercises.242Code Injection
Section HelpThis table shows the views that this attack pattern belongs to and top level categories within that view.
+ Execution Flow
  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.
+ Prerequisites
This attack targets most widely deployed feature rich email applications, including web based email programs.
+ Skills Required
[Level: Low]
To distribute email
+ Consequences
Section HelpThis table specifies different individual consequences associated with the attack pattern. The Scope identifies the security property that is violated, while the Impact describes the negative technical impact that arises if an adversary succeeds in their attack. The Likelihood provides information about how likely the specific consequence is expected to be seen relative to the other consequences in the list. For example, there may be high likelihood that a pattern will be used to achieve a certain impact, but a low likelihood that it will be exploited to achieve a different impact.
Execute Unauthorized Commands
+ 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
+ Example Instances
To:<someone@example.com> From:<badguy@example.com> 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.

+ References
[REF-1] G. Hoglund and G. McGraw. "Exploiting Software: How to Break Code". Addison-Wesley. 2004-02.
+ Content History
Submission DateSubmitterOrganization
2014-06-23CAPEC Content TeamThe MITRE Corporation
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Page Last Updated or Reviewed: December 17, 2020