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cwe:cn:definition:601

CWE-601:指向未可信站点的URL重定向(开放重定向)

Description Summary

A web application accepts a user-controlled input that specifies a link to an external site, and uses that link in a Redirect. This simplifies phishing attacks.

Extended Description

An http parameter may contain a URL value and could cause the web application to redirect the request to the specified URL. By modifying the URL value to a malicious site, an attacker may successfully launch a phishing scam and steal user credentials. Because the server name in the modified link is identical to the original site, phishing attempts have a more trustworthy appearance.

Background Details

Phishing is a general term for deceptive attempts to coerce private information from users that will be used for identity theft.

Likelihood of Exploit

Low to Medium

Common Consequences

Scope Technical Impace Note
Access_ControlBypass protection mechanism
Gain privileges / assume identity
The user may be redirected to an untrusted page that contains malware which may then compromise the user's machine. This will expose the user to extensive risk and the user's interaction with the web server may also be compromised if the malware conducts keylogging or other attacks that steal credentials, personally identifiable information (PII), or other important data.
Access_Control
Confidentiality
Other
Bypass protection mechanism
Gain privileges / assume identity
Other
The user may be subjected to phishing attacks by being redirected to an untrusted page. The phishing attack may point to an attacker controlled web page that appears to be a trusted web site. The phishers may then steal the user's credentials and then use these credentials to access the legitimate web site.

Detection Methods

Detection Method - 1

Manual Static Analysis

Since this weakness does not typically appear frequently within a single software package, manual white box techniques may be able to provide sufficient code coverage and reduction of false positives if all potentially-vulnerable operations can be assessed within limited time constraints.

The effectiveness and speed of manual analysis will be reduced if the there is not a centralized security mechanism, and the security logic is widely distributed throughout the software.
2013/05/30 09:37

Detection Method - 2

Automated Dynamic Analysis

Automated black box tools that supply URLs to every input may be able to spot Location header modifications, but test case coverage is a factor, and custom redirects may not be detected.

Detection Method - 3

Automated Static Analysis

Automated static analysis tools may not be able to determine whether input influences the beginning of a URL, which is important for reducing false positives.

Detection Method - 4

Other

Whether this issue poses a vulnerability will be subject to the intended behavior of the application. For example, a search engine might intentionally provide redirects to arbitrary URLs.

Detection Method - 5

Automated Static Analysis - Binary / Bytecode

According to SOAR, the following detection techniques may be useful:

Detection Method - 6

=== Dynamic Analysis with automated results interpretation === According to SOAR, the following detection techniques may be useful:

Detection Method - 7

Dynamic Analysis with manual results interpretation

According to SOAR, the following detection techniques may be useful:

Detection Method - 8

Manual Static Analysis - Source Code

According to SOAR, the following detection techniques may be useful:

Detection Method - 9

Automated Static Analysis - Source Code

According to SOAR, the following detection techniques may be useful:

Detection Method - 10

Architecture / Design Review

According to SOAR, the following detection techniques may be useful:

Potential Mitigations

Mitigation - 1

Implementation

Strategy:Input Validation

Assume all input is malicious. Use an “accept known good” input validation strategy, i.e., use a whitelist of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does.

When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, “boat” may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as “red” or “blue.”

Do not rely exclusively on looking for malicious or malformed inputs (i.e., do not rely on a blacklist). A blacklist is likely to miss at least one undesirable input, especially if the code's environment changes. This can give attackers enough room to bypass the intended validation. However, blacklists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright.

2013/05/30 09:37

Mitigation - 2

Architecture and Design

Use an intermediate disclaimer page that provides the user with a clear warning that they are leaving the current site. Implement a long timeout before the redirect occurs, or force the user to click on the link. Be careful to avoid XSS problems (CWE-79) when generating the disclaimer page.

Mitigation - 3

Architecture and Design

Strategy:Enforcement by Conversion

When the set of acceptable objects, such as filenames or URLs, is limited or known, create a mapping from a set of fixed input values (such as numeric IDs) to the actual filenames or URLs, and reject all other inputs.

For example, ID 1 could map to ”/login.asp” and ID 2 could map to “http://www.example.com/”. Features such as the ESAPI AccessReferenceMap [R.601.4] provide this capability.

2013/05/30 09:37

Mitigation - 4

Architecture and Design

Ensure that no externally-supplied requests are honored by requiring that all redirect requests include a unique nonce generated by the application [R.601.1]. Be sure that the nonce is not predictable (CWE-330).

Mitigation - 5

Architecture and Design Implementation

Strategy:Identify and Reduce Attack Surface

Understand all the potential areas where untrusted inputs can enter your software: parameters or arguments, cookies, anything read from the network, environment variables, reverse DNS lookups, query results, request headers, URL components, e-mail, files, filenames, databases, and any external systems that provide data to the application. Remember that such inputs may be obtained indirectly through API calls.

Many file inclusion problems occur because the programmer assumed that certain inputs could not be modified, especially for cookies and URL components.

2013/05/30 09:37

Mitigation - 6

Operation

Strategy:Firewall

Use an application firewall that can detect attacks against this weakness. It can be beneficial in cases in which the code cannot be fixed (because it is controlled by a third party), as an emergency prevention measure while more comprehensive software assurance measures are applied, or to provide defense in depth.

2013/05/30 09:37

Demonstrative Examples

Example - 1

The following code obtains a URL from the query string and then redirects the user to that URL.

$redirect_url = $_GET['url']; 
header("Location: " . $redirect_url); 

The problem with the above code is that an attacker could use this page as part of a phishing scam by redirecting users to a malicious site. For example, assume the above code is in the file example.php. An attacker could supply a user with the following link:

http://example.com/example.php?url=http://malicious.example.com 

The user sees the link pointing to the original trusted site (example.com) and does not realize the redirection that could take place.

Example - 2

The following code is a Java servlet that will receive a GET request with a url parameter in the request to redirect the browser to the address specified in the url parameter. The servlet will retrieve the url parameter value from the request and send a response to redirect the browser to the url address.

public class RedirectServlet extends HttpServlet { 
 
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { 
String query = request.getQueryString(); 
if (query.contains("url")) { 
String url = request.getParameter("url"); 
response.sendRedirect(url); 
 
} 
 
} 
 
} 

The problem with this Java servlet code is that an attacker could use the RedirectServlet as part of a e-mail phishing scam to redirect users to a malicious site. An attacker could send an HTML formatted e-mail directing the user to log into their account by including in the e-mail the following link:

<a href="http://bank.example.com/redirect?url=http://attacker.example.net">Click here to log in</a> 

The user may assume that the link is safe since the URL starts with their trusted bank, bank.example.com. However, the user will then be redirected to the attacker's web site (attacker.example.net) which the attacker may have made to appear very similar to bank.example.com. The user may then unwittingly enter credentials into the attacker's web page and compromise their bank account. A Java servlet should never redirect a user to a URL without verifying that the redirect address is a trusted site.

Observed Examples

Reference Description
CVE-2005-4206URL parameter loads the URL into a frame and causes it to appear to be part of a valid page.
CVE-2008-2951An open redirect vulnerability in the search script in the software allows remote attackers to redirect users to arbitrary web sites and conduct phishing attacks via a URL as a parameter to the proper function.
CVE-2008-2052Open redirect vulnerability in the software allows remote attackers to redirect users to arbitrary web sites and conduct phishing attacks via a URL in the proper parameter.
cwe/cn/definition/601.txt · 最后更改: 2014/09/04 14:43 (外部编辑)