CVE-2018-20060 in urllib3
Summary
by MITRE
urllib3 before version 1.23 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.
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Analysis
by VulDB Data Team • 12/27/2024
The vulnerability identified as CVE-2018-20060 represents a critical security flaw in the urllib3 library that affects versions prior to 1.23. This issue specifically pertains to how the library handles HTTP redirects when transitioning between different origins, creating a potential exposure of sensitive authentication credentials. The vulnerability stems from the library's failure to properly sanitize HTTP headers during cross-origin redirect operations, which can lead to unauthorized disclosure of authentication tokens and other sensitive information.
The technical flaw manifests when urllib3 processes HTTP redirects that involve changes in host, port, or scheme components of the URL. During such redirect operations, the library incorrectly preserves the Authorization header from the original request, even when the redirect destination resides on a completely different host or domain. This behavior violates fundamental security principles of credential handling and represents a direct violation of the principle of least privilege. The Authorization header typically contains sensitive authentication information such as bearer tokens, basic authentication credentials, or other forms of access tokens that should not be transmitted to unintended recipients.
From an operational impact perspective, this vulnerability creates significant security risks for applications that rely on urllib3 for HTTP communication. When an application makes a request that results in a cross-origin redirect, the attacker can potentially intercept the Authorization header and gain access to protected resources. The exposure becomes particularly dangerous when the redirect destination is an untrusted third-party server or when the redirect occurs over an insecure connection. This vulnerability can be exploited in various attack scenarios including man-in-the-middle attacks, where an attacker can capture the transmitted credentials, or in situations where applications use the same authentication tokens across different domains.
The security implications extend beyond simple credential exposure to encompass potential privilege escalation and unauthorized access to sensitive resources. When an application authenticates to a service and receives a redirect to a different host, the preservation of the Authorization header allows for the authentication context to be transferred to the new host without proper validation. This behavior directly violates security standards such as those outlined in CWE-384, which addresses the improper handling of authentication tokens during HTTP redirects, and aligns with ATT&CK technique T1071.004 for application layer protocol tunneling. The vulnerability also demonstrates poor security hygiene in header management and demonstrates a failure to implement proper access control measures during redirect operations.
Organizations using affected versions of urllib3 should implement immediate mitigations to protect their applications from this vulnerability. The primary recommendation involves upgrading to urllib3 version 1.23 or later, which contains the necessary fixes to properly handle cross-origin redirects. Additionally, applications should implement explicit header sanitization logic to remove sensitive headers before initiating cross-origin requests. Security teams should also consider implementing network monitoring to detect unusual redirect patterns that might indicate exploitation attempts. The fix implemented in version 1.23 ensures that Authorization headers are properly stripped during cross-origin redirects, preventing the unintended exposure of authentication credentials while maintaining proper functionality for legitimate cross-origin operations.