CWE-942: Permissive Cross-domain Security Policy with Untrusted Domains

Extended Description

If a cross-domain policy file includes domains that should not be trusted, such as when using wildcards under a high-level domain, then the application could be attacked by these untrusted domains. In many cases, the attack can be launched without the victim even being aware of it.

Code Examples & CVEs

Demonstrative Examples

These cross-domain policy files mean to allow Flash and Silverlight applications hosted on other domains to access its data:

Flash crossdomain.xml :

BadXML

<cross-domain-policy xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xsi:noNamespaceSchemaLocation="http://www.adobe.com/xml/schemas/PolicyFile.xsd"><allow-access-from domain="*.example.com"/><allow-access-from domain="*"/></cross-domain-policy>

These cross-domain policy files mean to allow Flash and Silverlight applications hosted on other domains to access its data:

Flash crossdomain.xml :

BadXML

<?xml version="1.0" encoding="utf-8"?><access-policy><cross-domain-access><policy><allow-from http-request-headers="SOAPAction"><domain uri="*"/></allow-from><grant-to><resource path="/" include-subpaths="true"/></grant-to></policy></cross-domain-access></access-policy>

Observed CVE Examples (5)

CVE-2012-2292

Product has a Silverlight cross-domain policy that does not restrict access to another application, which allows remote attackers to bypass the Same Origin Policy.

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CVE-2014-2049

The default Flash Cross Domain policies in a product allows remote attackers to access user files.

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CVE-2007-6243

Chain: Adobe Flash Player does not sufficiently restrict the interpretation and usage of cross-domain policy files, which makes it easier for remote attackers to conduct cross-domain and cross-site scripting (XSS) attacks.

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CVE-2008-4822

Chain: Adobe Flash Player and earlier does not properly interpret policy files, which allows remote attackers to bypass a non-root domain policy.

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CVE-2010-3636

Chain: Adobe Flash Player does not properly handle unspecified encodings during the parsing of a cross-domain policy file, which allows remote web servers to bypass intended access restrictions via unknown vectors.

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Source-backed guidance

Additional facts reviewed against primary or authoritative security sources.

Verify controls for CWE-942 with SSDF evidence

Use NIST SSDF verification and vulnerability-response practices to detect CWE-942, Permissive Cross-domain Security Policy with Untrusted Domains, throughout the product lifecycle. Derive review questions, static or dynamic checks, and negative tests from the CWE's causal behavior; define the components and lifecycle stages each check covers; and retain findings with enough evidence to distinguish the root cause from symptoms and impacts. Track escapes and false negatives, then improve the verification plan after every confirmed occurrence.

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

Apply Attack Surface Reduction controls for Permissive Cross-domain Security Policy with Untrusted Domains

MITRE associates mitigation with Architecture and Design, and Operation; the listed strategies include Attack Surface Reduction, and Environment Hardening; documented detection approaches include Automated Static Analysis. Use these source-defined anchors to turn CWE-942 into implementation, review, and verification checks for the affected component.

CWE-942: Permissive Cross-domain Security Policy with Untrusted Domains — MITRE CWE

Triage CWE-942 against known exploitation evidence

Use CISA's Known Exploited Vulnerabilities catalog to test whether a vulnerability mapped to CWE-942, Permissive Cross-domain Security Policy with Untrusted Domains, 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

Apply precise root-cause mapping to CWE-942

Apply MITRE's full root-cause mapping guidance when using CWE-942, Permissive Cross-domain Security Policy with Untrusted Domains. Separate weakness language from attacker prerequisites and technical impact, check the entry's abstraction and vulnerability-mapping notes, and prefer the most specific Base or Variant supported by the evidence. Record the rejected alternatives and require an independent review before the mapping is used for remediation trends or program metrics.

CVE to CWE Root Cause Mapping Guidance — MITRE CWE

Validate CWE-942 with root-cause mapping checks

Apply MITRE's root-cause mapping quick tips to CWE-942, Permissive Cross-domain Security Policy with Untrusted Domains. 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-942: Permissive Cross-domain Security Policy with Untrusted Domains?+

CWE-942: Permissive Cross-domain Security Policy with Untrusted Domains is a Common Weakness Enumeration (CWE) entry maintained by MITRE. The product uses a web-client protection mechanism such as a Content Security Policy (CSP) or cross-domain policy file, but the policy includes untrusted domains with which the web client is allowed to communicate. If a cross-domain policy file includes domains that should not be trusted, such as when using wildcards under a high-level domain, then the application could be attacked by these untrusted domains. In many cases, the attack can be launched without the victim even being aware of it.

What are the security consequences of Permissive Cross-domain Security Policy with Untrusted Domains?+

If exploited, CWE-942 (Permissive Cross-domain Security Policy with Untrusted Domains) it can compromise Confidentiality, Integrity, Availability and Access Control, leading to outcomes such as Execute Unauthorized Code or Commands, Bypass Protection Mechanism, Read Application Data and Varies by Context.

How do you prevent or mitigate Permissive Cross-domain Security Policy with Untrusted Domains?+

Recommended mitigations for CWE-942 include: Define a restrictive Content Security Policy [REF-1486] or cross-domain policy file. Avoid using wildcards in the CSP / cross-domain policy file. Any domain matching the wildcard expression will be implicitly trusted, and can perform two-way interaction with the target server. For Flash, modify crossdomain.xml to use meta-policy options such as 'master-only' or 'none' to reduce the possibility of an attacker planting extraneous cross-domain policy files on a server.

Which programming languages are affected by Permissive Cross-domain Security Policy with Untrusted Domains?+

CWE-942 commonly affects Not Language-Specific. Note that weaknesses are often language-agnostic patterns, so secure coding practices apply broadly.

What are real-world examples of Permissive Cross-domain Security Policy with Untrusted Domains?+

MITRE documents real CVEs mapped to CWE-942, including CVE-2012-2292, CVE-2014-2049, CVE-2007-6243, CVE-2008-4822 and CVE-2010-3636. You can look up the full details of each CVE, including CVSS scores and remediation guidance, on our CVE Lookup tool.

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

A CWE (Common Weakness Enumeration) like CWE-942 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-942: Permissive Cross-domain Security Policy with Untrusted Domains

Extended Description

Technical Details

Applicable To

Security Consequences

Scope

Impact

Mitigation Strategies

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Description

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Description

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Detection Methods

Code Examples & CVEs

Demonstrative Examples

Observed CVE Examples (5)

CWE Relationships

Parent Weaknesses

Source-backed guidance

Verify controls for CWE-942 with SSDF evidence

Apply Attack Surface Reduction controls for Permissive Cross-domain Security Policy with Untrusted Domains

Triage CWE-942 against known exploitation evidence

Apply precise root-cause mapping to CWE-942

Validate CWE-942 with root-cause mapping checks

Frequently Asked Questions

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