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A misconfiguration flaw was found in Keycloak. This issue can allow an attacker to redirect users to an arbitrary URL if a 'Valid Redirect URI' is set to http://localhost or http://127.0.0.1, enabling sensitive information such as authorization codes to be exposed to the attacker, potentially leading to session hijacking.
CVSS 3.1 Base Score 6.8. CVSS Attack Vector: network. CVSS Attack Complexity: high. CVSS Vector: (CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:N).
CVSS 3.1 Base Score 6.1. CVSS Attack Vector: network. CVSS Attack Complexity: low. CVSS Vector: (CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N).
The following code obtains a URL from the query string and then redirects the user to that 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.comThe 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.
}
}}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.
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