CVE-2011-3415 in .NET Framework
Summary
by MITRE
Open redirect vulnerability in the Forms Authentication feature in the ASP.NET subsystem in Microsoft .NET Framework 2.0 SP2, 3.5 SP1, 3.5.1, and 4.0 allows remote attackers to redirect users to arbitrary web sites and conduct phishing attacks via a crafted return URL, aka "Insecure Redirect in .NET Form Authentication Vulnerability."
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Analysis
by VulDB Data Team • 03/20/2021
The CVE-2011-3415 vulnerability represents a critical open redirect flaw within the Forms Authentication mechanism of Microsoft's ASP.NET framework affecting multiple versions including .NET Framework 2.0 SP2, 3.5 SP1, 3.5.1, and 4.0. This vulnerability stems from insufficient validation of return URLs in the authentication process, creating a pathway for malicious actors to manipulate the redirection behavior of authenticated applications. The flaw specifically targets the handling of the redirect URL parameter that is typically used to direct users back to their intended destination after successful authentication. When applications rely on the default Forms Authentication behavior without proper input sanitization, attackers can craft malicious URLs containing crafted return parameters that point to attacker-controlled domains.
The technical implementation of this vulnerability resides in the way ASP.NET processes the return URL parameter during the authentication workflow. The framework fails to adequately validate or sanitize the redirect target, allowing attackers to inject arbitrary URLs that bypass normal security checks. This occurs because the system accepts user-supplied redirect URLs without proper verification of their legitimacy or domain ownership. The vulnerability is classified under CWE-601 as an Open Redirect vulnerability, where the application redirects users to an untrusted destination without proper validation. The flaw operates at the application layer and can be exploited through simple URL manipulation techniques, making it particularly dangerous as it requires minimal technical expertise to execute successful attacks.
The operational impact of CVE-2011-3415 extends beyond simple redirection, creating significant opportunities for phishing and social engineering attacks. Attackers can craft convincing malicious URLs that appear legitimate to users, directing them to fake authentication pages that mimic the target application's interface. This creates a high probability of user deception as victims may believe they are navigating to a trusted website when in fact they are being redirected to malicious domains. The vulnerability enables attackers to harvest credentials, collect sensitive user information, or deliver malware through the redirected sessions. Security professionals categorize this vulnerability under the ATT&CK framework as part of the T1566 technique for Phishing, specifically targeting the credential access phase of the attack lifecycle. The ease of exploitation makes this vulnerability particularly dangerous in environments where users may not be security-aware and where applications do not implement proper URL validation measures.
Mitigation strategies for CVE-2011-3415 require both immediate patching and architectural improvements to prevent similar vulnerabilities. Organizations should immediately apply Microsoft security updates for the affected .NET Framework versions to resolve the underlying validation flaw. Additionally, developers should implement explicit URL validation logic that checks redirect targets against a predefined whitelist of trusted domains or employs strict URL parsing to ensure that redirect destinations are within the application's trusted scope. The implementation of proper input validation and output encoding practices can prevent attackers from injecting malicious redirect parameters. Organizations should also consider implementing additional security controls such as secure session management, enhanced authentication protocols, and regular security testing to identify and remediate similar vulnerabilities. Network-level controls and web application firewalls can provide additional protection layers, though they should not be relied upon as the sole defense mechanism. The vulnerability underscores the importance of proper security coding practices and the need for continuous security assessment of authentication mechanisms in web applications.