CVE-2018-15798 in Concourse
Summary
by MITRE
Pivotal Concourse Release, versions 4.x prior to 4.2.2, login flow allows redirects to untrusted websites. A remote unauthenticated attacker could convince a user to click on a link using the oAuth redirect link with an untrusted website and gain access to that user's access token in Concourse.
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Analysis
by VulDB Data Team • 06/19/2023
The vulnerability identified as CVE-2018-15798 affects Pivotal Concourse Release versions 4.x prior to 4.2.2 and represents a critical security flaw in the authentication system's redirect mechanism. This issue specifically impacts the login flow that utilizes OAuth redirect functionality, creating a pathway for malicious actors to exploit the system's trust model. The vulnerability stems from insufficient validation of redirect URLs within the OAuth authentication process, allowing attackers to manipulate the redirection behavior and potentially capture user credentials or access tokens. The flaw exists in the application's handling of OAuth redirect URIs, where the system fails to properly verify or sanitize the destination URLs before initiating redirects. This weakness creates a dangerous scenario where users may be unknowingly redirected to malicious sites while attempting to authenticate with the Concourse platform.
The technical implementation of this vulnerability aligns with CWE-601, which describes open redirect vulnerabilities where applications redirect users to untrusted websites without proper validation. The flaw operates by leveraging the OAuth authorization flow, where legitimate authentication requests can be manipulated to redirect users to attacker-controlled domains. When users click on malicious links containing crafted OAuth redirect parameters, they are automatically redirected to the attacker's website, potentially exposing their access tokens or other sensitive authentication information. The attack requires minimal user interaction beyond clicking a malicious link, making it particularly dangerous in phishing scenarios. The vulnerability demonstrates a classic case of insufficient input validation in web applications, where the system assumes all redirect URLs are trustworthy without proper sanitization or domain verification.
The operational impact of this vulnerability extends beyond simple credential theft, as access tokens obtained through this method can provide attackers with elevated privileges within the Concourse environment. An attacker who successfully captures a user's access token could potentially access build pipelines, modify configurations, view sensitive data, or even execute unauthorized operations within the continuous integration and deployment system. The vulnerability affects any user who authenticates through the affected Concourse versions, including administrators and regular team members, creating a broad attack surface. The remote nature of the exploit means that attackers do not require physical access to the system or network, making the vulnerability particularly concerning for organizations that rely on Concourse for their CI/CD operations. This flaw could enable attackers to gain persistent access to build environments and potentially compromise the integrity of software delivery pipelines.
Organizations should immediately implement mitigation strategies including updating to Concourse version 4.2.2 or later, which contains the necessary patches to address the redirect validation issue. Security measures should include implementing strict redirect URL validation mechanisms that only allow redirection to pre-approved domains or implementing a whitelist of trusted redirect endpoints. The system should also enforce proper URL sanitization and validation before any redirect operations occur, ensuring that all redirect targets are verified against a trusted list. Network-level protections such as firewall rules and web application firewalls can help detect and block suspicious redirect attempts. Additionally, organizations should consider implementing user education programs to raise awareness about phishing attempts and suspicious links. The mitigation approach should align with ATT&CK technique T1566, which covers social engineering methods including spearphishing with links, emphasizing the need for both technical controls and user awareness. Regular security audits and penetration testing should be conducted to ensure that similar vulnerabilities are not present in other authentication mechanisms or application components.