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CWE Glossary Definition
CWE-942: Permissive Cross-domain Security Policy with Untrusted Domains
Weakness ID: 942Vulnerability Mapping: ALLOWED This CWE ID may be used to map to real-world vulnerabilities
Abstraction: Variant Variant - a weakness that is linked to a certain type of product, typically involving a specific language or technology. More specific than a Base weakness. Variant level weaknesses typically describe issues in terms of 3 to 5 of the following dimensions: behavior, property, technology, language, and resource.View customized information:For users who are interested in more notional aspects of a weakness. Example: educators, technical writers, and project/program managers. For users who are concerned with the practical application and details about the nature of a weakness and how to prevent it from happening. Example: tool developers, security researchers, pen-testers, incident response analysts. For users who are mapping an issue to CWE/CAPEC IDs, i.e., finding the most appropriate CWE for a specific issue (e.g., a CVE record). Example: tool developers, security researchers. For users who wish to see all available information for the CWE/CAPEC entry. For users who want to customize what details are displayed.×
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Description
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.
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.
Common Consequences
This table specifies different individual consequences
associated with the weakness. The Scope identifies the application security area that is
violated, while the Impact describes the negative technical impact that arises if an
adversary succeeds in exploiting this weakness. 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 weakness will be
exploited to achieve a certain impact, but a low likelihood that it will be exploited to
achieve a different impact.
Impact Details Execute Unauthorized Code or Commands; Bypass Protection Mechanism; Read Application Data; Varies by Context
Scope: Confidentiality, Integrity, Availability, Access Control With an overly permissive policy file, an attacker may be able to bypass the web browser's same-origin policy and conduct many of the same attacks seen in Cross-Site Scripting (CWE-79). An attacker can exploit the weakness to transfer private information from the victim's machine to the attacker, manipulate or steal cookies that may include session information, create malicious requests to a web site on behalf of the victim, or execute malicious code on the end user systems. Other damaging attacks include the disclosure of end user files, installation of Trojan horse programs, redirecting the user to some other page or site, running ActiveX controls (under Microsoft Internet Explorer) from sites that a user perceives as trustworthy, and modifying presentation of content.
Potential MitigationsPhase(s) Mitigation Architecture and Design; Operation
Strategy: Attack Surface Reduction
Define a restrictive Content Security Policy [REF-1486] or cross-domain policy file.Architecture and Design; Operation
Strategy: Attack Surface Reduction
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.Architecture and Design; Operation
Strategy: Environment Hardening
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.
Relationships
This table shows the weaknesses and high level categories that are related to this
weakness. These relationships are defined as ChildOf, ParentOf, MemberOf and give insight to
similar items that may exist at higher and lower levels of abstraction. In addition,
relationships such as PeerOf and CanAlsoBe are defined to show similar weaknesses that the user
may want to explore.
Relevant to the view "Research Concepts" (View-1000)
Nature Type ID Name ChildOf 
Base - a weakness that is still mostly independent of a resource or technology, but with sufficient details to provide specific methods for detection and prevention. Base level weaknesses typically describe issues in terms of 2 or 3 of the following dimensions: behavior, property, technology, language, and resource.
183 Permissive List of Allowed Inputs ChildOf 
Class - a weakness that is described in a very abstract fashion, typically independent of any specific language or technology. More specific than a Pillar Weakness, but more general than a Base Weakness. Class level weaknesses typically describe issues in terms of 1 or 2 of the following dimensions: behavior, property, and resource.
863 Incorrect Authorization ChildOf
Class - a weakness that is described in a very abstract fashion, typically independent of any specific language or technology. More specific than a Pillar Weakness, but more general than a Base Weakness. Class level weaknesses typically describe issues in terms of 1 or 2 of the following dimensions: behavior, property, and resource.
923 Improper Restriction of Communication Channel to Intended Endpoints CanPrecede
Class - a weakness that is described in a very abstract fashion, typically independent of any specific language or technology. More specific than a Pillar Weakness, but more general than a Base Weakness. Class level weaknesses typically describe issues in terms of 1 or 2 of the following dimensions: behavior, property, and resource.
668 Exposure of Resource to Wrong Sphere
Relevant to the view "Architectural Concepts" (View-1008)
Nature Type ID Name MemberOf 
Category - a CWE entry that contains a set of other entries that share a common characteristic.
1011 Authorize Actors
Background DetailsIn HTTP/HTTPS, policies such as the Same Origin Policy prevent web clients from loading resources from (or making requests to) domains that did not match the web site's own domain, e.g., Javascript or other code hosted on third-party servers. These policies are strictly enforced by browsers and other products. However, these restrictions can be reduced using mechanisms that specify other domains that are allowed to be contacted from the original site, such as Content Security Policy (CSP) or cross-domain policy files (e.g., "crossdomain.xml" in Adobe Flash or Reader, "clientaccesspolicy.xml" in Silverlight, etc.). These mechanisms define a list of domains from which a client is allowed to make cross-domain requests. When making a cross-domain request, the client will first look for the policy file on the target server. If it is found, and the domain hosting the application is explicitly allowed to make requests, the request is made.
Modes
Of IntroductionThe different Modes of Introduction provide information
about how and when this
weakness may be introduced. The Phase identifies a point in the life cycle at which
introduction
may occur, while the Note provides a typical scenario related to introduction during the
given
phase.
Phase Note Implementation Architecture and Design COMMISSION: This weakness refers to an incorrect design related to an architectural security tactic.
Applicable PlatformsThis listing shows possible areas for which the given
weakness could appear. These
may be for specific named Languages, Operating Systems, Architectures, Paradigms,
Technologies,
or a class of such platforms. The platform is listed along with how frequently the given
weakness appears for that instance.
Languages Class: Not Language-Specific (Undetermined Prevalence)
Technologies Class: Web Based (Undetermined Prevalence)
Web Server (Undetermined Prevalence)
Demonstrative ExamplesExample 1
These cross-domain policy files mean to allow Flash and Silverlight applications hosted on other domains to access its data:
Flash crossdomain.xml :
(bad code)Example Language: XML<cross-domain-policy xmlns:xsi="https://www.w3.org/2001/XMLSchema-instance"
xsi:noNamespaceSchemaLocation="https://www.adobe.com/xml/schemas/PolicyFile.xsd">
<allow-access-from domain="*.example.com"/>
<allow-access-from domain="*"/>
</cross-domain-policy>Silverlight clientaccesspolicy.xml :
(bad code)Example Language: XML<?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>These entries are far too permissive, allowing any Flash or Silverlight application to send requests. A malicious application hosted on any other web site will be able to send requests on behalf of any user tricked into executing it.
Selected Observed
ExamplesNote: this is a curated list of examples for users to understand the variety of ways in which this weakness can be introduced. It is not a complete list of all CVEs that are related to this CWE entry.
Reference Description 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.The default Flash Cross Domain policies in a product allows remote attackers to access user files.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.Chain: Adobe Flash Player and earlier does not properly interpret policy files, which allows remote attackers to bypass a non-root domain policy.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.
Weakness OrdinalitiesOrdinality Description Primary(where the weakness exists independent of other weaknesses) Detection
MethodsMethod Details Automated Static Analysis
Automated static analysis, commonly referred to as Static Application Security Testing (SAST), can find some instances of this weakness by analyzing source code (or binary/compiled code) without having to execute it. Typically, this is done by building a model of data flow and control flow, then searching for potentially-vulnerable patterns that connect "sources" (origins of input) with "sinks" (destinations where the data interacts with external components, a lower layer such as the OS, etc.)Effectiveness: High
Memberships
This MemberOf Relationships table shows additional CWE Categories and Views that
reference this weakness as a member. This information is often useful in understanding where a
weakness fits within the context of external information sources.
Nature Type ID Name MemberOf Category - a CWE entry that contains a set of other entries that share a common characteristic.1349 OWASP Top Ten 2021 Category A05:2021 - Security Misconfiguration MemberOf Category - a CWE entry that contains a set of other entries that share a common characteristic.1396 Comprehensive Categorization: Access Control MemberOf Category - a CWE entry that contains a set of other entries that share a common characteristic.1437 OWASP Top Ten 2025 Category A02:2025 - Security Misconfiguration
Vulnerability Mapping NotesUsage ALLOWED (this CWE ID may be used to map to real-world vulnerabilities)Reason Acceptable-Use Rationale
This CWE entry is at the Variant level of abstraction, which is a preferred level of abstraction for mapping to the root causes of vulnerabilities. Comments
Carefully read both the name and description to ensure that this mapping is an appropriate fit. Do not try to 'force' a mapping to a lower-level Base/Variant simply to comply with this preferred level of abstraction. References[REF-1486] OWASP. "Content Security Policy Cheat Sheet".
<https://cheatsheetseries.owasp.org/cheatsheets/Content_Security_Policy_Cheat_Sheet.html>. (URL validated: 2025-09-08)[REF-943] Apurva Udaykumar. "Setting a crossdomain.xml file for HTTP streaming". Adobe. 2012-11-19.
<https://web.archive.org/web/20121124184922/https://www.adobe.com/devnet/adobe-media-server/articles/cross-domain-xml-for-streaming.html>. (URL validated: 2023-04-07)[REF-944] Adobe. "Cross-domain policy for Flash movies". Adobe.
<https://kb2.adobe.com/cps/142/tn_14213.html>.[REF-945] Microsoft Corporation. "HTTP Communication and Security with Silverlight".
<https://learn.microsoft.com/en-us/previous-versions/windows/silverlight/dotnet-windows-silverlight/cc838250(v=vs.95)?redirectedfrom=MSDN>. (URL validated: 2023-04-07)[REF-946] Microsoft Corporation. "Network Security Access Restrictions in Silverlight".
<https://learn.microsoft.com/en-us/previous-versions/windows/silverlight/dotnet-windows-silverlight/cc645032(v=vs.95)>. (URL validated: 2023-04-07)[REF-947] Dongseok Jang, Aishwarya Venkataraman, G. Michael Sawka and Hovav Shacham. "Analyzing the Crossdomain Policies of Flash Applications". 2011-05.
<https://cseweb.ucsd.edu/~hovav/dist/crossdomain.pdf>. Content
History SubmissionsSubmission Date Submitter Organization 2014-06-05
(CWE 2.7, 2014-06-23)CWE Content Team MITRE Created by MITRE with input from members of the CWE-Research mailing list. ContributionsContribution Date Contributor Organization 2022-08-23
(CWE 4.18, 2025-09-09)Jagjeet Singh Rakuten Kobo Inc. Suggested new entry for misconfigured CSP allowing JavaScript, leading to changes in CWE-942 to make it more general 
ModificationsModification Date Modifier Organization 2025-12-11
(CWE 4.19, 2025-12-11)CWE Content Team MITRE updated Applicable_Platforms, Relationships, Weakness_Ordinalities 2025-09-09
(CWE 4.18, 2025-09-09)CWE Content Team MITRE updated Background_Details, Common_Consequences, Description, Name, Potential_Mitigations, References 2024-02-29
(CWE 4.14, 2024-02-29)CWE Content Team MITRE updated Demonstrative_Examples 2023-06-29 CWE Content Team MITRE updated Mapping_Notes, Relationships 2023-04-27 CWE Content Team MITRE updated Detection_Factors, References, Relationships 2023-01-31 CWE Content Team MITRE updated Description, Relationships 2021-10-28 CWE Content Team MITRE updated Relationships 2020-06-25 CWE Content Team MITRE updated Description, Name 2020-02-24 CWE Content Team MITRE updated Applicable_Platforms, Relationships 2019-06-20 CWE Content Team MITRE updated Relationships 2017-11-08 CWE Content Team MITRE updated Modes_of_Introduction, References, Relationships Previous Entry NamesChange Date Previous Entry Name 2020-02-26 Overly Permissive Cross-domain Whitelist 2025-09-09 Permissive Cross-domain Policy with Untrusted Domains More information is available — Please edit the custom filter or select a different filter.Page Last Updated: December 11, 2025
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