CVE-2016-3687 in BIG-IP APM
Summary
by MITRE
Open redirect vulnerability in F5 BIG-IP APM 11.2.1, 11.4.x, 11.5.x, and 11.6.x before 11.6.0 HF6 and Edge Gateway 11.2.1, when using multi-domain single sign-on (SSO), allows remote attackers to redirect users to arbitrary web sites and conduct phishing attacks via a base64-encoded URL in the SSO_ORIG_URI parameter.
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Analysis
by VulDB Data Team • 08/24/2022
The vulnerability identified as CVE-2016-3687 represents a critical open redirect flaw within F5 BIG-IP APM and Edge Gateway products that specifically affects versions 11.2.1, 11.4.x, 11.5.x, and 11.6.x prior to 11.6.0 HF6. This security weakness occurs in the context of multi-domain single sign-on implementations where the system fails to properly validate user-supplied URLs, creating an avenue for malicious actors to manipulate the authentication flow. The vulnerability manifests when the SSO_ORIG_URI parameter contains a base64-encoded URL that bypasses normal validation mechanisms, allowing attackers to craft deceptive redirection sequences that can fool users into visiting malicious websites. This particular flaw operates at the application layer and demonstrates a fundamental failure in input sanitization and validation processes that should occur during the SSO workflow.
The technical implementation of this vulnerability stems from improper handling of the SSO_ORIG_URI parameter within the F5 BIG-IP APM and Edge Gateway systems. When multi-domain SSO is enabled, the system expects to redirect users to legitimate service endpoints after authentication, but the base64 decoding process fails to properly validate the resulting URL against a whitelist of approved domains. This allows attackers to encode malicious URLs in the SSO_ORIG_URI parameter, which when decoded and processed by the application, results in unauthorized redirection to phishing sites or other malicious destinations. The vulnerability specifically exploits the trust relationship between the authentication system and the user, leveraging the legitimate SSO mechanism to deliver malicious payloads. From a cybersecurity perspective, this vulnerability maps directly to CWE-601 Open Redirect and aligns with ATT&CK technique T1566.001 for Phishing through Social Engineering, as it enables attackers to create convincing phishing campaigns that appear legitimate to end users.
The operational impact of this vulnerability extends beyond simple redirection attacks, as it creates a significant risk for credential theft and system compromise. Attackers can leverage this flaw to redirect authenticated users to phishing sites that closely mimic legitimate service portals, potentially capturing credentials or other sensitive information. The vulnerability is particularly dangerous in enterprise environments where users trust the authentication system and may not suspect that a legitimate SSO process could be compromised. Additionally, the broad scope of affected versions means that numerous organizations running these F5 products are potentially exposed to this threat, with the risk persisting until the affected systems are patched or properly configured to prevent the vulnerable parameter from being processed. Organizations utilizing multi-domain SSO configurations are especially at risk, as the vulnerability directly targets the core functionality of these security mechanisms.
Organizations should implement immediate mitigations including applying the vendor-provided security patches for F5 BIG-IP APM and Edge Gateway versions affected by this vulnerability, specifically targeting the 11.6.0 HF6 release or later. Network administrators should also consider implementing additional controls such as URL filtering and monitoring for suspicious SSO_ORIG_URI parameter usage, particularly in web application firewalls or similar security appliances. The mitigation strategy should include disabling or restricting the use of base64-encoded parameters in SSO flows where possible, and implementing strict domain whitelisting for all redirection targets. From a defensive perspective, this vulnerability highlights the importance of proper input validation in authentication systems and demonstrates how seemingly benign functionality can be exploited for malicious purposes. Security teams should also consider implementing user education programs to help identify potential phishing attempts that may leverage this vulnerability, as the social engineering aspect of this attack can be particularly effective when users are unaware of the underlying technical vulnerability.