CVE-2011-2192 in cURL
Summary
by MITRE
The Curl_input_negotiate function in http_negotiate.c in libcurl 7.10.6 through 7.21.6, as used in curl and other products, always performs credential delegation during GSSAPI authentication, which allows remote servers to impersonate clients via GSSAPI requests.
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Analysis
by VulDB Data Team • 11/14/2021
The vulnerability identified as CVE-2011-2192 resides within the libcurl library's HTTP GSSAPI authentication implementation, specifically in the Curl_input_negotiate function located in http_negotiate.c. This flaw affects versions 7.10.6 through 7.21.6 of the library and has been widely adopted across numerous applications including the curl command-line tool and various web clients. The issue stems from the library's handling of GSSAPI authentication mechanisms where it unconditionally performs credential delegation regardless of the server's authentication requirements or the client's security preferences. This behavior violates fundamental security principles by automatically forwarding client credentials to potentially untrusted servers without proper authorization checks.
The technical implementation flaw manifests in how libcurl processes GSSAPI authentication responses during HTTP negotiations. When a client establishes a connection with a server that supports GSSAPI authentication, the library automatically attempts to delegate the client's credentials to the server as part of the authentication process. This delegation occurs irrespective of whether the server actually requires delegated credentials or whether the client has explicitly configured credential delegation. The function fails to properly evaluate the authentication context and instead follows a hardcoded path that always enables credential delegation, creating an attack surface where malicious servers can exploit this behavior to impersonate legitimate clients. This vulnerability directly maps to CWE-305 authentication bypass weakness where the system fails to properly verify authentication credentials and allows unauthorized access through improper credential handling.
The operational impact of this vulnerability extends beyond simple credential theft to encompass full client impersonation capabilities for remote adversaries. An attacker who controls a malicious HTTP server can exploit this vulnerability to obtain and reuse client credentials for authentication against other services that trust the delegated credentials. This creates a chain reaction where compromised client credentials can be used to access additional systems and resources within the network, effectively enabling lateral movement and persistent access. The vulnerability is particularly dangerous in enterprise environments where users may have elevated privileges and where credential delegation is commonly used for single sign-on systems. The attack vector requires only that a client connects to a malicious server that supports GSSAPI authentication, making it a significant risk for any system that uses libcurl for HTTP communications and has GSSAPI authentication enabled.
Mitigation strategies for CVE-2011-2192 focus on both immediate patching and operational security improvements. The primary solution involves upgrading to libcurl versions 7.21.7 or later where the vulnerability has been addressed through proper credential delegation controls and conditional authentication handling. Organizations should also implement network segmentation and monitoring to detect unusual GSSAPI authentication patterns that might indicate exploitation attempts. Security configurations should be reviewed to disable GSSAPI authentication when it is not strictly required, and administrators should implement proper credential management practices including regular credential rotation and monitoring for unauthorized credential usage. Additionally, organizations should consider implementing network-based protections such as firewalls and intrusion detection systems that can detect and block GSSAPI authentication traffic to untrusted servers. This vulnerability demonstrates the importance of proper authentication context handling and credential delegation controls in security-sensitive applications, aligning with ATT&CK technique T1550.003 for use of stolen credentials and T1078.002 for valid accounts with the specific emphasis on credential delegation weaknesses in authentication systems.