The web application accepts a user-controlled input that specifies a link to an external site, and uses that link in a redirect.

Primary

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

Open Redirect

Cross-site Redirect

Cross-domain Redirect

Unvalidated Redirect

Drive-by download
an attack, sometimes enabled by open redirects, which redirects the victim to a site that automatically triggers a download action of malicious software or files

Architecture and Design
OMISSION: This weakness is caused by missing a security tactic during the architecture and design phase.

Implementation

Low

Access Control
Bypass Protection Mechanism
Gain Privileges or Assume Identity
The user may be redirected to an untrusted page
that contains malware which may then compromise the
user's system. In some cases, an open redirect can also
enable the immediate download of a file without the
user's permission, because the redirection to an
external site may lead to endpoints on those sites that
automatically trigger a download action ("drive-by
download" [REF-1478]). This will expose the user to
extensive risk. 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 or Assume Identity
Other
By modifying the URL value to a malicious site, an attacker may successfully launch a phishing scam. 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. Because the server name in the modified link is identical to the original site, phishing attempts have a more trustworthy appearance.

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.
High

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.

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.

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.)
High

Automated Static Analysis - Binary or Bytecode

According to SOAR [REF-1479], the following detection techniques may be useful:

Highly cost effective:

Bytecode Weakness Analysis - including disassembler + source code weakness analysis
Binary Weakness Analysis - including disassembler + source code weakness analysis

High

Dynamic Analysis with Automated Results Interpretation

According to SOAR [REF-1479], the following detection techniques may be useful:

Highly cost effective:

Web Application Scanner
Web Services Scanner
Database Scanners

High

Dynamic Analysis with Manual Results Interpretation

According to SOAR [REF-1479], the following detection techniques may be useful:

Highly cost effective:

Fuzz Tester
Framework-based Fuzzer

High

Manual Static Analysis - Source Code

According to SOAR [REF-1479], the following detection techniques may be useful:

Highly cost effective:

Manual Source Code Review (not inspections)

High

Automated Static Analysis - Source Code

According to SOAR [REF-1479], the following detection techniques may be useful:

Highly cost effective:

Source code Weakness Analyzer
Context-configured Source Code Weakness Analyzer

High

Architecture or Design Review

According to SOAR [REF-1479], the following detection techniques may be useful:

Highly cost effective:

Formal Methods / Correct-By-Construction

Cost effective for partial coverage:

Inspection (IEEE 1028 standard) (can apply to requirements, design, source code, etc.)

High

Implementation
Input Validation

Assume all input is malicious. Use an "accept known good" input validation strategy, i.e., use a list 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. This 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, denylists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright.
Use a list of approved URLs or domains to be used for redirection.

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.

Architecture and Design
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 [REF-45] provide this capability.

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 [REF-483]. Be sure that the nonce is not predictable (CWE-330).
Note that this can be bypassed using XSS (CWE-79).

Architecture and Design
Implementation
Attack Surface Reduction

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 open redirect problems occur because the programmer assumed that certain inputs could not be modified, such as cookies and hidden form fields.

Operation
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 [REF-1481].
Moderate
An application firewall might not cover all possible input vectors. In addition, attack techniques might be available to bypass the protection mechanism, such as using malformed inputs that can still be processed by the component that receives those inputs. Depending on functionality, an application firewall might inadvertently reject or modify legitimate requests. Finally, some manual effort may be required for customization.

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.

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 an 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.

CVE-2005-4206
URL parameter loads the URL into a frame and causes it to appear to be part of a valid page.
https://www.cve.org/CVERecord?id=CVE-2005-4206

CVE-2008-2951
An 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.
https://www.cve.org/CVERecord?id=CVE-2008-2951

CVE-2008-2052
Open 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.
https://www.cve.org/CVERecord?id=CVE-2008-2052

CVE-2020-11053
Chain: Go-based Oauth2 reverse proxy can send the authenticated user to another site at the end of the authentication flow. A redirect URL with HTML-encoded whitespace characters can bypass the validation (CWE-1289) to redirect to a malicious site (CWE-601)
https://www.cve.org/CVERecord?id=CVE-2020-11053

38
URl Redirector Abuse

SFP24
Tainted input to command

Allowed
This CWE entry is at the Base level of abstraction, which is a preferred level of abstraction for mapping to the root causes of vulnerabilities.
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.

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.

Anonymous Tool Vendor (under NDA)
2007-05-07
Draft 6
2007-05-07

Eric Dalci
Cigital
2008-07-01
updated Potential_Mitigations, Time_of_Introduction

CWE Content Team
MITRE
2008-09-08
updated Alternate_Terms, Background_Details, Description, Detection_Factors, Likelihood_of_Exploit, Name, Relationships, Observed_Example, Taxonomy_Mappings

CWE Content Team
MITRE
2008-10-03
updated References and Observed_Examples

CWE Content Team
MITRE
2008-10-14
updated Alternate_Terms, Observed_Examples, References

CWE Content Team
MITRE
2009-03-10
updated Relationships

CWE Content Team
MITRE
2009-05-27
updated Name

CWE Content Team
MITRE
2009-12-28
updated Demonstrative_Examples, Detection_Factors, Likelihood_of_Exploit, Potential_Mitigations

CWE Content Team
MITRE
2010-02-16
updated Applicable_Platforms, Common_Consequences, Detection_Factors, Potential_Mitigations, Related_Attack_Patterns, Relationships, Taxonomy_Mappings

CWE Content Team
MITRE
2010-04-05
updated Demonstrative_Examples

CWE Content Team
MITRE
2010-06-21
updated Common_Consequences, Potential_Mitigations, References, Relationships

CWE Content Team
MITRE
2010-09-27
updated Potential_Mitigations

CWE Content Team
MITRE
2011-06-01
updated Common_Consequences

CWE Content Team
MITRE
2011-06-27
updated Relationships

CWE Content Team
MITRE
2011-09-13
updated Potential_Mitigations, References

CWE Content Team
MITRE
2012-05-11
updated Relationships

CWE Content Team
MITRE
2012-10-30
updated Potential_Mitigations

CWE Content Team
MITRE
2013-07-17
updated References, Relationships

CWE Content Team
MITRE
2014-07-30
updated Detection_Factors, Relationships, Taxonomy_Mappings

CWE Content Team
MITRE
2015-12-07
updated Relationships

CWE Content Team
MITRE
2017-11-08
updated Likelihood_of_Exploit, Modes_of_Introduction, References, Relationships, Taxonomy_Mappings

CWE Content Team
MITRE
2019-01-03
updated Related_Attack_Patterns

CWE Content Team
MITRE
2019-06-20
updated Relationships, Type

CWE Content Team
MITRE
2020-02-24
updated Applicable_Platforms, Potential_Mitigations, Relationships

CWE Content Team
MITRE
2020-06-25
updated Potential_Mitigations

CWE Content Team
MITRE
2021-10-28
updated Relationships

CWE Content Team
MITRE
2022-04-28
updated Relationships

CWE Content Team
MITRE
2022-10-13
updated Observed_Examples

CWE Content Team
MITRE
2023-01-31
updated Related_Attack_Patterns

CWE Content Team
MITRE
2023-04-27
updated Description, Detection_Factors, References, Relationships

CWE Content Team
MITRE
2023-06-29
updated Mapping_Notes

CWE Content Team
MITRE
2024-02-29
4.14
2024-02-29
updated Demonstrative_Examples

CWE Content Team
MITRE
2024-11-19
4.16
2024-11-19
updated Alternate_Terms, Common_Consequences, Description, Diagram, Other_Notes

CWE Content Team
MITRE
2025-09-09
4.18
2025-09-09
updated Alternate_Terms, Common_Consequences, Detection_Factors, Potential_Mitigations, References

CWE Content Team
MITRE
2025-12-11
4.19
2025-12-11
updated Applicable_Platforms, Relationships, Weakness_Ordinalities

Michal Biesiada
2023-11-25
4.18
2025-09-09
suggested that CWE include drive-by downloads and contributed references

Unsafe URL Redirection
URL Redirection to Untrusted Site
URL Redirection to Untrusted Site (aka 'Open Redirect')