CVE-2020-23015 in OPNsense
Summary
by MITRE • 05/04/2021
An open redirect issue was discovered in OPNsense through 20.1.5. The redirect parameter "url" in login page was not filtered and can redirect user to any website.
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Analysis
by VulDB Data Team • 05/07/2021
The vulnerability identified as CVE-2020-23015 represents a critical open redirect flaw within the OPNsense firewall and router management interface. This issue affects versions through 20.1.5 and stems from improper input validation in the login page's redirect functionality. The vulnerability specifically involves the "url" parameter which is used to determine where users should be redirected after successful authentication. When this parameter is not properly sanitized or validated, it creates an avenue for malicious actors to manipulate the redirect behavior.
The technical implementation of this flaw allows attackers to craft malicious URLs that contain arbitrary redirect targets in the url parameter. When a victim clicks such a link and authenticates through the vulnerable OPNsense interface, they will be automatically redirected to the attacker-controlled destination. This creates a dangerous phishing opportunity where users might be tricked into visiting malicious sites while believing they are accessing legitimate administrative interfaces. The vulnerability operates at the application layer and specifically targets the authentication flow of the web-based management interface.
From an operational impact perspective, this vulnerability significantly undermines the security posture of affected OPNsense deployments. Attackers can leverage this flaw to conduct phishing campaigns that appear legitimate to users who are already authenticated to the network. The redirect mechanism, which should only allow redirection to internal resources, becomes a vector for external malicious content delivery. This opens the door to credential theft, malware distribution, and further network infiltration attempts. The vulnerability affects any organization relying on OPNsense for network security who have not updated to patched versions, creating a persistent threat vector that can be exploited without requiring elevated privileges.
Organizations should immediately implement mitigations including updating to patched versions of OPNsense where available, implementing strict input validation for redirect parameters, and configuring network-level restrictions to prevent unauthorized external access to the management interface. The vulnerability aligns with CWE-601 Open Redirect weakness and maps to attack techniques in the MITRE ATT&CK framework under Initial Access and Credential Access phases. Network administrators should also consider implementing additional monitoring for suspicious redirect patterns and user authentication activities that might indicate exploitation attempts. The security community has classified this as a high-risk vulnerability due to its potential for widespread abuse in social engineering campaigns.