CVE-2009-0037 in curl
Summary
by MITRE
The redirect implementation in curl and libcurl 5.11 through 7.19.3, when CURLOPT_FOLLOWLOCATION is enabled, accepts arbitrary Location values, which might allow remote HTTP servers to (1) trigger arbitrary requests to intranet servers, (2) read or overwrite arbitrary files via a redirect to a file: URL, or (3) execute arbitrary commands via a redirect to an scp: URL.
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Analysis
by VulDB Data Team • 12/22/2024
The vulnerability described in CVE-2009-0037 represents a critical security flaw in the curl and libcurl libraries that affects versions 5.11 through 7.19.3. This issue stems from improper handling of HTTP redirect responses when the CURLOPT_FOLLOWLOCATION option is enabled, creating a significant attack surface that allows remote servers to manipulate client behavior in dangerous ways. The flaw operates at the application layer and demonstrates a classic case of insufficient input validation and sanitization in network communication libraries that are widely deployed across operating systems and applications.
The technical implementation of this vulnerability exploits the trust model inherent in HTTP redirect mechanisms. When a client encounters a 301 or 302 redirect response, it typically follows the Location header to retrieve the resource from a new location. However, the vulnerable curl implementations failed to properly validate or sanitize these Location values, allowing attackers to inject malicious URLs that would be followed without proper restrictions. This behavior directly violates the principle of least privilege and creates opportunities for attackers to bypass normal network security controls. The vulnerability specifically enables three distinct attack vectors that leverage different URL schemes to achieve malicious objectives.
The operational impact of this vulnerability is severe and multifaceted. Attackers can leverage the redirect mechanism to force clients to make arbitrary requests to internal network resources, effectively bypassing firewalls and network segmentation controls. This capability allows for internal network reconnaissance and potentially unauthorized access to sensitive systems. Additionally, the ability to redirect to file: URLs enables attackers to read or overwrite arbitrary files on the client system, potentially leading to data exfiltration, system compromise, or denial of service conditions. The scp: URL redirection capability introduces even more dangerous possibilities, as it could enable command execution on the client system, depending on the underlying implementation of scp protocol handling.
This vulnerability maps directly to multiple CWE entries including CWE-20: Improper Input Validation, CWE-73: External Control of File Name or Path, and CWE-120: Buffer Overflow, reflecting the layered nature of the security issues present. From an adversarial perspective, this flaw aligns with several ATT&CK techniques including T1071.004: Application Layer Protocol: DNS, T1046: Network Service Scanning, and T1105: Remote File Copy. The vulnerability demonstrates how seemingly benign HTTP redirect functionality can be weaponized to create attack chains that bypass traditional network security controls. Organizations using vulnerable versions of curl or libcurl face significant risk of internal network compromise, data leakage, and system exploitation, particularly in environments where clients may encounter untrusted web content.
The recommended mitigations for this vulnerability include immediate upgrade to curl or libcurl versions 7.19.4 or later, where the redirect handling has been properly fixed. Organizations should also implement network-level controls such as URL filtering and proxy configuration to restrict access to potentially dangerous URL schemes. Additionally, application developers should review their use of curl libraries and ensure proper input validation is implemented even when relying on library functions. System administrators should monitor for unusual network traffic patterns that might indicate exploitation attempts, particularly connections to internal network resources or unusual file system access patterns. The vulnerability underscores the critical importance of maintaining up-to-date security libraries and the potential consequences of failing to address known security issues promptly.