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.
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Explain the attack pattern CAPEC-41: Using Meta-characters in E-mail Headers to Inject Malicious Payloads: how it unfolds, what it needs and how to prevent and detect it in my systems. Use https://capec.mitre.org/data/definitions/41.html and https://cve.bz/cve/capec/41?via=ask-ai-copy, which lists recent CVEs with the weaknesses it exploits. Cite the sources.Opens a third-party assistant; its answer is its own, not cve.bz's. The prompt holds only this attack pattern's id and public links.
How the attack unfolds
Experiment
They probe what they found.
[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.
2 techniques
- 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.
Exploit
They carry out the attack.
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.
1 technique
- 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
- Low skill
To distribute email
Consequences
| Impact | Affects | Note |
|---|---|---|
| Execute Unauthorized Commands | Confidentiality, Integrity, Availability | Run Arbitrary Code |
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
Weaknesses it exploits
- CWE-88 Improper Neutralization of Argument Delimiters in a Command
- CWE-150 Improper Neutralization of Escape, Meta, or Control Sequences
- CWE-697 Incorrect Comparison
Recent CVEs with these weaknesses
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Argument injection in Ivanti Sentry before version 10.8.3 and 10.7.4 allows a remote authenticated attacker with admin privileges to execute arbitrary on-disk binaries.
- 6.6CVE-2026-125672
A flaw was found in cockpit-storaged. A Tang keyserver address read from a clevis token in a LUKS header is concatenated into curl's argument vector without a "--" separator. An address beginning with "-" is parsed by curl as an option ins…
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A vulnerability was identified in nushell up to 0.116.1. Impacted is the function escape_bytes of the file crates/nu-json/src/ser.rs of the component Data Conversion Handler. The manipulation leads to improper neutralization of escape, met…
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- 5.3CVE-2026-123369
compose-lint is a Docker Compose security linter that identifies dangerous misconfigurations before deployment. Prior to 0.31.0, compose-lint prints attacker-controlled service names, environment keys, file lines, and other Compose text wi…
- 6.7CVE-2026-82830
IBM Guardium Data Protection 12.2.4 could allow a remote authenticated attacker to execute arbitrary commands due to improper neutralization of argument delimiters.
The newest records naming one of them. Each weakness's page lists them all.
Related attack patterns
Examples
Example 1
To:<someone@example.com>
From:<badguy@example.com>
Header<SCRIPT>payme</SCRIPT>def: whateverMeta-characters are among the most valuable tools attackers have to deceive users into taking some action on …
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.
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