CVE-2018-25091 in urllib3
Summary
by MITRE • 10/25/2023
urllib3 before 1.24.2 does not remove the authorization HTTP header when following a cross-origin redirect (i.e., a redirect that differs in host, port, or scheme). This can allow for credentials in the authorization header to be exposed to unintended hosts or transmitted in cleartext. NOTE: this issue exists because of an incomplete fix for CVE-2018-20060 (which was case-sensitive).
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Analysis
by VulDB Data Team • 11/02/2023
The vulnerability identified as CVE-2018-25091 represents a critical security flaw in the urllib3 library that affects versions prior to 1.24.2. This issue specifically addresses the improper handling of HTTP authorization headers during cross-origin redirect operations, creating a significant risk for credential exposure and data leakage. The vulnerability emerged from an incomplete remediation approach for a previous related issue, CVE-2018-20060, which itself was a case-sensitive implementation flaw that failed to properly address the broader scope of authorization header handling across different network boundaries.
The technical flaw manifests when urllib3 processes HTTP redirects that involve changes in host, port, or scheme parameters. During such cross-origin redirect scenarios, the library fails to strip or remove the authorization header from the request before forwarding it to the new destination. This behavior occurs because the implementation does not adequately distinguish between same-origin and cross-origin redirect conditions, leading to the automatic propagation of sensitive authentication tokens and credentials. The authorization header, which typically contains bearer tokens, basic authentication credentials, or other sensitive authentication information, becomes inadvertently transmitted to potentially untrusted third-party servers that may not be authorized to receive such information.
The operational impact of this vulnerability extends beyond simple credential exposure, creating potential attack vectors for various malicious activities including man-in-the-middle attacks, credential harvesting, and unauthorized access to protected resources. When applications using vulnerable urllib3 versions make requests that result in cross-origin redirects, any authentication tokens present in the authorization header are automatically included in subsequent requests to the redirected host. This creates a scenario where credentials intended for one service or domain can be transmitted to entirely different hosts, potentially exposing sensitive information to attackers who control those alternative endpoints. The risk is particularly pronounced when redirects occur to hosts that are not under the control of the original application owner or when the redirect targets endpoints that lack proper security controls.
The vulnerability directly relates to CWE-200, which addresses "Information Exposure," and aligns with several ATT&CK techniques including T1566 for "Phishing" and T1071 for "Application Layer Protocol" where credential exposure occurs through protocol manipulation. Organizations using vulnerable urllib3 versions face significant risk of unauthorized access to their systems, particularly in environments where applications make extensive use of HTTP redirects or interact with third-party services that may perform cross-origin redirects. The issue is exacerbated in scenarios involving API gateways, microservices architectures, or applications that rely on OAuth flows where authorization tokens may be inadvertently shared with unintended recipients during redirect operations.
Mitigation strategies for CVE-2018-25091 require immediate patching of urllib3 to version 1.24.2 or later, which includes the complete fix for the authorization header handling during cross-origin redirects. Organizations should conduct comprehensive inventory assessments to identify all systems and applications utilizing vulnerable urllib3 versions, particularly focusing on web applications, API consumers, and services that perform HTTP communication with external endpoints. Additionally, security teams should implement monitoring for unauthorized credential exposure patterns and consider implementing network-level controls to detect and prevent unusual cross-origin redirect behavior. Regular security assessments and dependency updates should be prioritized to prevent similar issues from arising in the future, with particular attention to the proper handling of authentication headers across different network contexts and protocol boundaries.