CVE-2016-8616 in macOS
Summary
by MITRE
A flaw was found in curl before version 7.51.0 When re-using a connection, curl was doing case insensitive comparisons of user name and password with the existing connections. This means that if an unused connection with proper credentials exists for a protocol that has connection-scoped credentials, an attacker can cause that connection to be reused if s/he knows the case-insensitive version of the correct password.
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 10/07/2022
The vulnerability identified as CVE-2016-8616 represents a critical authentication bypass flaw in the curl command-line tool and library versions prior to 7.51.0. This issue stems from improper handling of connection reuse mechanisms within the HTTP authentication framework, creating a significant security risk for applications that rely on curl for network communications. The flaw specifically affects scenarios where curl maintains persistent connections and performs credential validation during connection reuse operations.
The technical implementation of this vulnerability resides in curl's connection management logic where it performs case-insensitive comparisons of username and password credentials when determining whether to reuse an existing connection. This behavior violates the fundamental security principle that authentication credentials should be handled with strict case sensitivity to prevent unauthorized access. When curl encounters a connection that has already been established with valid credentials, it should require exact credential matching to ensure proper authentication. However, the flawed implementation allows for case-insensitive matching, which creates a pathway for attackers to exploit the connection reuse mechanism.
This vulnerability operates under the context of HTTP authentication protocols where connection-scoped credentials are used for protocol-specific authentication. The flaw specifically impacts HTTP Basic Authentication, HTTP Digest Authentication, and other protocols that maintain credentials within connection contexts. Attackers can exploit this weakness by establishing a connection with valid credentials, then attempting to reuse that connection by providing a case-insensitive variation of the correct password. The vulnerability is particularly dangerous because it can be leveraged by attackers who have partial knowledge of target credentials, making it a significant concern for environments where curl is used extensively for automated processes and web scraping operations.
The operational impact of CVE-2016-8616 extends beyond simple credential theft, as it can enable attackers to perform unauthorized operations on behalf of legitimate users. This vulnerability is classified under CWE-287 - Improper Handling of Authentication Credentials, which addresses the improper management of authentication information. The attack vector aligns with ATT&CK technique T1078 - Valid Accounts, where adversaries leverage legitimate credentials to gain access to systems. Organizations using curl for automated tasks, web services, or security scanning tools face elevated risk, as the vulnerability can be exploited through simple network traffic manipulation without requiring complex attack chains. The flaw particularly affects environments where curl is used in conjunction with authentication proxies or services that maintain persistent connections.
Mitigation strategies for this vulnerability require immediate patching of curl to version 7.51.0 or later, which implements proper case-sensitive credential comparison during connection reuse operations. System administrators should conduct comprehensive inventory audits to identify all systems utilizing vulnerable curl versions and prioritize remediation efforts. Additional protective measures include implementing network segmentation to limit curl access to sensitive resources, monitoring connection reuse patterns for anomalous behavior, and configuring applications to avoid connection reuse when authentication is involved. Security teams should also consider implementing intrusion detection systems that can identify potential exploitation attempts through unusual authentication patterns or connection reuse behaviors. The vulnerability demonstrates the importance of proper credential handling in network libraries and the critical need for maintaining up-to-date security patches across all system components. Organizations should establish robust patch management processes to prevent similar issues from arising in the future, particularly focusing on the security implications of connection management and credential validation in network libraries.