CVE-2009-5144 in Mod-gnutls
Summary
by MITRE
mod-gnutls does not validate client certificates when "GnuTLSClientVerify require" is set in a directory context, which allows remote attackers to spoof clients via a crafted certificate.
Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.
Analysis
by VulDB Data Team • 02/02/2021
The vulnerability described in CVE-2009-5144 affects the mod_gnutls Apache module, which implements gnutls protocol support for secure web communications. This issue specifically manifests when the GnuTLSClientVerify require directive is configured within a directory context rather than at the server level. The flaw represents a critical configuration error that bypasses client certificate validation mechanisms, creating a security gap that can be exploited by remote attackers to impersonate legitimate clients.
The technical root cause of this vulnerability lies in the improper handling of client certificate validation within the mod_gnutls module when processing directory-level configurations. When GnuTLSClientVerify require is set in a directory context, the module fails to properly validate the presented client certificates against the configured verification requirements. This misconfiguration allows attackers to present forged certificates that would normally be rejected by the system, effectively bypassing the intended authentication controls. The vulnerability specifically impacts Apache web servers configured with mod_gnutls and operating under directory-level client certificate verification settings.
The operational impact of this vulnerability is significant as it enables man-in-the-middle attacks and unauthorized access to protected resources. Remote attackers can exploit this weakness by presenting crafted client certificates that appear valid to the server but are actually forged or obtained through compromise. This allows them to gain access to services that should only be available to authenticated clients, potentially leading to data breaches, privilege escalation, and unauthorized system access. The vulnerability undermines the fundamental security model of client certificate authentication, which is commonly used in enterprise environments for secure authentication and authorization.
Security practitioners should implement immediate mitigations including updating to patched versions of mod_gnutls, ensuring proper server-level configuration of GnuTLSClientVerify directives, and conducting thorough security audits of Apache configurations. The vulnerability aligns with CWE-284 Access Control Issues, specifically related to insufficient access control mechanisms and improper privilege management. From an ATT&CK framework perspective, this vulnerability maps to T1566 Credential Access through the exploitation of weak authentication mechanisms and T1071 Application Layer Protocol for establishing unauthorized connections. Organizations should also consider implementing additional monitoring and logging controls to detect unusual certificate validation patterns and ensure proper certificate lifecycle management practices are in place to prevent similar issues in the future.