CVE-2017-18262 in Learn
Summary
by MITRE
Blackboard Learn (Since at least 17th of October 2017) has allowed Unvalidated Redirects on any signed-in user through its endpoints for handling Shibboleth logins, as demonstrated by a webapps/bb-auth-provider-shibboleth-BBLEARN/execute/shibbolethLogin?returnUrl= URI.
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Analysis
by VulDB Data Team • 03/08/2023
The vulnerability identified as CVE-2017-18262 represents a critical security flaw in Blackboard Learn platforms that has persisted since October 2017, affecting organizations relying on Shibboleth authentication mechanisms. This issue stems from improper validation of redirect parameters within the authentication flow, specifically within the bb-auth-provider-shibboleth-BBLEARN/execute/shibbolethLogin endpoint. The flaw allows malicious actors to manipulate the returnUrl parameter, potentially leading to unauthorized redirection of authenticated users to malicious websites or attack vectors. The vulnerability specifically targets the Shibboleth login handler, which is commonly used in educational institutions and enterprise environments for single sign-on authentication, making it particularly concerning given the widespread adoption of Blackboard Learn in academic and corporate settings.
The technical implementation of this vulnerability resides in the lack of proper input validation and sanitization within the Shibboleth authentication handler. When a user attempts to log in through Shibboleth, the system accepts a return URL parameter that is intended to redirect users back to their original destination after successful authentication. However, the application fails to validate or sanitize this parameter, allowing attackers to inject arbitrary URLs. This creates a classic open redirect vulnerability where an attacker can craft a malicious link that, when clicked by an authenticated user, will redirect them to a phishing site or malicious domain. The vulnerability is particularly dangerous because it leverages the trust relationship between the user and the authenticated session, making it more likely that users will follow the redirect without suspicion.
The operational impact of this vulnerability extends beyond simple redirection attacks, as it can serve as a stepping stone for more sophisticated attacks within the targeted organization. An attacker could exploit this vulnerability to create phishing campaigns that appear legitimate to users who are already authenticated to the Blackboard system, potentially harvesting credentials or sensitive information from the target environment. The vulnerability also aligns with attack patterns documented in the MITRE ATT&CK framework under the T1566 technique for Phishing, where attackers use legitimate authentication mechanisms to gain access to user sessions. Additionally, this flaw can be combined with other attacks such as credential stuffing or session hijacking, creating a more comprehensive attack vector against the organization's authentication infrastructure. The persistent nature of this vulnerability since 2017 indicates that many organizations may have remained exposed to this risk for extended periods, potentially allowing attackers to establish persistent access patterns.
Organizations should implement immediate mitigations including input validation and sanitization of all redirect parameters, implementing a whitelist of approved redirect URLs, and ensuring that the application only accepts redirects to trusted domains. The vulnerability maps to CWE-601 which specifically addresses open redirect vulnerabilities, emphasizing the importance of proper input validation and domain restriction in authentication flows. Security teams should also conduct comprehensive audits of all authentication endpoints to identify similar vulnerabilities, particularly in custom authentication handlers or third-party integrations. Additionally, implementing proper logging and monitoring of authentication flows can help detect suspicious redirect patterns and potential exploitation attempts. Organizations should also consider implementing web application firewalls that can detect and block malicious redirect attempts, while ensuring that all users are educated about the risks of clicking suspicious links, even when they appear to come from trusted sources. The vulnerability demonstrates the critical importance of maintaining proper authentication security practices and the potential consequences of failing to validate redirect parameters in enterprise authentication systems.