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

Description

The product uses a cross-domain policy file that includes domains that should not be trusted.

Extended Description

A cross-domain policy file ("crossdomain.xml" in Flash and "clientaccesspolicy.xml" in Silverlight) defines a list of domains from which a server is allowed to make cross-domain requests. When making a cross-domain request, the Flash or Silverlight 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. Therefore, if a cross-domain policy file includes domains that should not be trusted, such as when using wildcards, then the application could be attacked by these untrusted domains. An overly permissive policy file allows many of the same attacks seen in Cross-Site Scripting (CWE-79). Once the user has executed a malicious Flash or Silverlight application, they are vulnerable to a variety of attacks. The attacker could transfer private information, such as cookies that may include session information, from the victim's machine to the attacker. The attacker could send malicious requests to a web site on behalf of the victim, which could be especially dangerous to the site if the victim has administrator privileges to manage that site. In many cases, the attack can be launched without the victim even being aware of it.

ThreatScore

Threat Mapped score: 0.0

Industry: Finiancial

Threat priority: Unclassified

Observed Examples (CVEs)

CVE: 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.
CVE: CVE-2014-2049

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

Related Attack Patterns (CAPEC)

N/A

Attack TTPs

N/A

Modes of Introduction

Phase	Note
Implementation	N/A
Architecture and Design	COMMISSION: This weakness refers to an incorrect design related to an architectural security tactic.

Common Consequences

Impact: Execute Unauthorized Code or Commands, Bypass Protection Mechanism, Read Application Data, Varies by Context — Notes: An attacker may be able to bypass the web browser's same-origin policy. An attacker can exploit the weakness to manipulate or steal cookies, create requests that can be mistaken for those of a valid user, compromise confidential information, or execute malicious code on the end user systems for a variety of nefarious purposes. 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 Mitigations

Architecture and Design: Avoid using wildcards in the cross-domain policy file. Any domain matching the wildcard expression will be implicitly trusted, and can perform two-way interaction with the target server. (N/A)
Architecture and Design: 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. (N/A)
Architecture and Design: 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. (N/A)

Applicable Platforms

None (Not Language-Specific, Undetermined)

Demonstrative Examples

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

Body: 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>

Notes

No notes available.

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