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.)
CWE-942 Variant Incomplete
Permissive Cross-domain Security Policy with Untrusted Domains
This vulnerability occurs when a web application's cross-domain security policy, like a Content Security Policy (CSP), explicitly allows communication with untrusted or overly permissive external…
Definition
What is CWE-942?
This vulnerability occurs when a web application's cross-domain security policy, like a Content Security Policy (CSP), explicitly allows communication with untrusted or overly permissive external domains.
A permissive cross-domain policy undermines a key web security control. By listing untrusted domains or using overly broad wildcards (e.g., *.example.com), you grant those external sites the ability to interact with your application's data and user session, effectively inviting potential attackers into a trusted context.
Attackers hosted on these permitted domains can often launch exploits, such as data theft or session hijacking, without any visible warning to the end user. This makes the vulnerability particularly dangerous, as a compromise can occur silently during normal browsing, bypassing the intended protections of the security policy.
Auswirkungen in der Praxis
Real-world CVEs caused by CWE-942
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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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The default Flash Cross Domain policies in a product allows remote attackers to access user files.
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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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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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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.
Wie Angreifer es ausnutzen
Angreiferpfad Schritt für Schritt
- 1
These cross-domain policy files mean to allow Flash and Silverlight applications hosted on other domains to access its data:
- 2
Flash crossdomain.xml :
- 3
Silverlight clientaccesspolicy.xml :
- 4
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.
Verwundbares Codebeispiel
Vulnerable XML
Flash crossdomain.xml :
<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> Sicheres Codebeispiel
Secure pseudo
// Validate, sanitize, or use a safe API before reaching the sink.
function handleRequest(input) {
const safe = validateAndEscape(input);
return executeWithGuards(safe);
} What changed: the unsafe sink is replaced (or the input is validated/escaped) so the same payload no longer triggers the weakness.
Präventions-Checkliste
How to prevent CWE-942
- Architecture and Design / Operation Define a restrictive Content Security Policy [REF-1486] or cross-domain policy file.
- Architecture and Design / Operation 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 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.
Erkennungssignale
How to detect CWE-942
Plexicus erkennt CWE-942 automatisch und öffnet in unter 60 Sekunden einen Fix-PR.
Codex Remedium scannt jeden Commit, identifiziert genau diese Schwachstelle und liefert einen reviewer-ready Pull Request mit dem Patch. Keine Tickets. Keine Hand-offs.
Häufig gestellte Fragen Was ist CWE-942?
Wie gravierend ist CWE-942?
Welche Sprachen oder Plattformen sind von CWE-942 betroffen?
Wie kann ich CWE-942 verhindern?
Wie erkennt und behebt Plexicus CWE-942?
Wo erfahre ich mehr über CWE-942?
Frequently asked questions
Was ist CWE-942?
This vulnerability occurs when a web application's cross-domain security policy, like a Content Security Policy (CSP), explicitly allows communication with untrusted or overly permissive external domains.
Wie gravierend ist CWE-942?
MITRE hat für diese Schwachstelle keine Exploit-Wahrscheinlichkeit veröffentlicht. Behandle sie als mittlere Auswirkung, bis dein Threat Model anderes belegt.
Welche Sprachen oder Plattformen sind von CWE-942 betroffen?
MITRE lists the following affected platforms: Web Based.
Wie kann ich CWE-942 verhindern?
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.
Wie erkennt und behebt Plexicus CWE-942?
Die SAST-Engine von Plexicus erkennt die Datenfluss-Signatur von CWE-942 bei jedem Commit. Bei einem Treffer öffnet unser Codex-Remedium-Agent einen Fix-PR mit korrigiertem Code, Tests und einer einzeiligen Zusammenfassung für den Reviewer.
Wo erfahre ich mehr über CWE-942?
MITRE veröffentlicht die kanonische Definition unter https://cwe.mitre.org/data/definitions/942.html. Für ergänzende Hinweise kannst du auch die OWASP- und NIST-Dokumentation heranziehen.
Verwandte Schwachstellen
Weaknesses related to CWE-942
CWE-863 Parent
Incorrect Authorization
This vulnerability occurs when an application checks if a user is allowed to perform an action or access data, but the check is flawed or…
CWE-1244 Sibling
Internal Asset Exposed to Unsafe Debug Access Level or State
This vulnerability occurs when a system's debug or test interface supports multiple access levels, but an internal asset is incorrectly…
CWE-551 Sibling
Incorrect Behavior Order: Authorization Before Parsing and Canonicalization
This vulnerability occurs when a web server checks access permissions before fully processing and normalizing a URL, potentially allowing…
CWE-639 Sibling
Authorization Bypass Through User-Controlled Key
This vulnerability occurs when an application's authorization system fails to verify that a user is allowed to access specific data before…
CWE-647 Sibling
Use of Non-Canonical URL Paths for Authorization Decisions
This vulnerability occurs when an application's authorization logic relies on specific URL paths but fails to enforce a single,…
CWE-804 Sibling
Guessable CAPTCHA
This vulnerability occurs when a CAPTCHA challenge is too easy for automated bots to solve, either by guessing or using pattern…
CWE-668 Kann vorausgehen
Exposure of Resource to Wrong Sphere
This vulnerability occurs when an application unintentionally makes a resource accessible to users or systems that should not have…
Ressourcen
Further reading
- MITRE — offizielle CWE-942 https://cwe.mitre.org/data/definitions/942.html
- Content Security Policy Cheat Sheet https://cheatsheetseries.owasp.org/cheatsheets/Content_Security_Policy_Cheat_Sheet.html
- Setting a crossdomain.xml file for HTTP streaming https://web.archive.org/web/20121124184922/http://www.adobe.com/devnet/adobe-media-server/articles/cross-domain-xml-for-streaming.html
- Cross-domain policy for Flash movies http://kb2.adobe.com/cps/142/tn_14213.html
- 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
- Network Security Access Restrictions in Silverlight https://learn.microsoft.com/en-us/previous-versions/windows/silverlight/dotnet-windows-silverlight/cc645032(v=vs.95)
- Analyzing the Crossdomain Policies of Flash Applications http://cseweb.ucsd.edu/~hovav/dist/crossdomain.pdf
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