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 Variante Incomplet
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…
Définition
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.
Impact réel
Real-world CVEs caused by CWE-942
-
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.
Comment les attaquants l'exploitent
Parcours de l'attaquant étape par étape
- 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.
Exemple de code vulnérable
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> Exemple de code sécurisé
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.
Liste de contrôle de prévention
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.
Signaux de détection
How to detect CWE-942
CWE-942
Don't catalog this weakness. Prove it's reachable.
Plexicus turns CWE catalogs into evidence: every CWE-pattern is matched against your real code graph, reach is proven on a sandbox clone, and verified findings ship as reviewed PRs.
Questions fréquentes Qu'est-ce que CWE-942 ?
Quelle est la gravité de CWE-942 ?
Quels langages ou plateformes sont affectés par CWE-942 ?
Comment puis-je prévenir CWE-942 ?
Comment Plexicus détecte et corrige CWE-942 ?
Où puis-je en savoir plus sur CWE-942 ?
Frequently asked questions
Qu'est-ce que 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.
Quelle est la gravité de CWE-942 ?
MITRE n'a pas publié de note de probabilité d'exploitation pour cette faiblesse. Traitez-la comme un impact moyen jusqu'à ce que votre modèle de menace prouve le contraire.
Quels langages ou plateformes sont affectés par CWE-942 ?
MITRE lists the following affected platforms: Web Based.
Comment puis-je prévenir CWE-942 ?
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.
Comment Plexicus détecte et corrige CWE-942 ?
Le moteur SAST de Plexicus reconnaît la signature de flux de données de CWE-942 à chaque commit. Lorsqu'une correspondance est trouvée, notre agent Codex Remedium ouvre une PR de correction avec le code corrigé, les tests et un résumé d'une ligne pour le relecteur.
Où puis-je en savoir plus sur CWE-942 ?
MITRE publie la définition canonique à https://cwe.mitre.org/data/definitions/942.html. Vous pouvez également consulter la documentation OWASP et NIST pour des conseils adjacents.
Faiblesses associées
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 Frère
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 Frère
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 Frère
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 Frère
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 Frère
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 Peut précéder
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…
Ressources
Further reading
- MITRE — CWE-942 officiel 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
Prêt à valider l'essentiel ?
Prêt à valider ce qui compte.
Plexicus est Proof-Driven AppSec : findings validés, compréhension contextuelle et remédiation relue — ancrée dans la preuve, scopée avec vous.