CVE-2016-0755 in macOS
Summary
by MITRE
The ConnectionExists function in lib/url.c in libcurl before 7.47.0 does not properly re-use NTLM-authenticated proxy connections, which might allow remote attackers to authenticate as other users via a request, a similar issue to CVE-2014-0015.
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Analysis
by VulDB Data Team • 09/20/2022
The vulnerability described in CVE-2016-0755 resides within the libcurl library's connection handling mechanism, specifically in the ConnectionExists function located in lib/url.c. This flaw represents a critical authentication bypass issue that affects versions of libcurl prior to 7.47.0, creating a significant security risk for applications that rely on NTLM-authenticated proxy connections. The vulnerability stems from improper connection re-use behavior when handling NTLM authentication, which allows malicious actors to potentially impersonate legitimate users within network environments that depend on proxy authentication mechanisms.
The technical root cause of this vulnerability lies in the improper management of connection state during NTLM authentication processes. When libcurl establishes a connection through an NTLM-authenticated proxy, the ConnectionExists function fails to correctly validate whether an existing connection can be safely re-used for subsequent requests. This occurs because the function does not properly verify that the authentication context remains valid when re-purposing connections, leading to a scenario where authentication credentials from one user session might be incorrectly applied to another user's request. This flaw directly relates to CWE-284, which addresses improper access control, and specifically manifests as a weakness in connection management that enables unauthorized access through credential re-use.
The operational impact of this vulnerability extends beyond simple authentication bypass to encompass potential data compromise and privilege escalation within networked environments. Attackers can exploit this vulnerability to make authenticated requests through proxy servers using credentials from previous sessions, potentially gaining access to resources that should be restricted to specific users or groups. This issue is particularly dangerous in enterprise environments where NTLM authentication is commonly used for proxy server access, as it could allow attackers to access internal resources, view sensitive information, or perform actions on behalf of authenticated users. The vulnerability operates at the application layer and can be exploited remotely, making it particularly concerning for web applications and services that utilize libcurl for network communications.
Mitigation strategies for CVE-2016-0755 focus primarily on upgrading to libcurl version 7.47.0 or later, where the connection re-use logic has been properly implemented to prevent NTLM credential leakage. Organizations should conduct thorough vulnerability assessments to identify applications using vulnerable versions of libcurl and prioritize patching efforts accordingly. Additional defensive measures include implementing network-level controls to monitor and restrict proxy access, configuring proxy servers with stricter authentication requirements, and establishing connection pooling policies that prevent automatic re-use of authenticated connections. Security teams should also consider implementing monitoring solutions that can detect anomalous authentication patterns or unexpected connection re-use behaviors that might indicate exploitation attempts. The ATT&CK framework categorizes this vulnerability under credential access techniques, specifically targeting the use of valid credentials to access systems and data without proper authorization, making it a significant concern for organizations implementing security controls that rely on proper authentication mechanisms.