CVE-2016-8624 in macOS
Summary
by MITRE
curl before version 7.51.0 doesn't parse the authority component of the URL correctly when the host name part ends with a '#' character, and could instead be tricked into connecting to a different host. This may have security implications if you for example use an URL parser that follows the RFC to check for allowed domains before using curl to request them.
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Analysis
by VulDB Data Team • 10/07/2022
The vulnerability identified as CVE-2016-8624 represents a critical flaw in the curl command-line tool and library versions prior to 7.51.0, specifically concerning URL parsing behavior that can lead to host name confusion and potential security bypasses. This issue stems from curl's improper handling of the authority component within URLs when the hostname portion terminates with a hash character. The technical implementation flaw occurs during the URL parsing process where curl fails to correctly interpret the boundary between the hostname and any subsequent fragment identifier, creating a scenario where the tool may establish connections to unintended destinations.
The operational impact of this vulnerability extends beyond simple parsing errors to potentially enable sophisticated attack vectors involving domain validation bypasses. When applications utilize curl for making HTTP requests and employ URL parsers that strictly follow RFC specifications to validate allowed domains, this flaw creates a dangerous discrepancy between expected and actual behavior. An attacker could craft malicious URLs where the hash character at the end of a hostname portion would cause curl to interpret the connection target differently than intended, potentially redirecting traffic to unauthorized servers. This behavior directly violates the principle of least privilege and can undermine security controls that rely on proper URL validation mechanisms.
The vulnerability aligns with CWE-1206, which addresses improper handling of URL authority components, and demonstrates characteristics consistent with ATT&CK technique T1190, specifically the use of valid accounts for initial access and privilege escalation. The flaw essentially creates a path for attackers to manipulate network traffic routing through carefully crafted URLs that exploit the difference between RFC-compliant parsing and curl's actual implementation. This discrepancy can be particularly dangerous in environments where curl is used programmatically within security-sensitive applications, as it may allow adversaries to bypass domain allowlists and access restricted resources through seemingly legitimate network requests.
Organizations should prioritize immediate patching of curl installations to version 7.51.0 or later, as this vulnerability can be exploited without user interaction and may not require additional authentication. Security teams should conduct thorough audits of applications that depend on curl for network operations, particularly those implementing domain validation controls. Additional mitigations include implementing network-level restrictions, monitoring for unusual connection patterns, and validating all URL inputs through multiple verification mechanisms. The vulnerability serves as a reminder of the importance of consistent URL parsing behavior across security tools and the potential for subtle implementation flaws to create significant security risks in network communications.