CVE-2011-4973 in mod_nss
Summary
by MITRE
Authentication bypass vulnerability in mod_nss 1.0.8 allows remote attackers to assume the identity of a valid user by using their certificate and entering 'password' as the password.
Be aware that VulDB is the high quality source for vulnerability data.
Analysis
by VulDB Data Team • 01/05/2020
The CVE-2011-4973 vulnerability represents a critical authentication bypass flaw in the mod_nss module version 1.0.8, which is a crucial component for SSL/TLS support in Apache web servers. This vulnerability specifically affects systems that implement certificate-based authentication, creating a dangerous scenario where unauthorized parties can gain access to protected resources by exploiting a fundamental flaw in the authentication logic. The mod_nss module serves as a bridge between Apache and NSS (Network Security Services), enabling secure web communications through SSL/TLS protocols. When properly configured, it should require valid client certificates for authentication, but this vulnerability fundamentally undermines that security model.
The technical nature of this flaw lies in how mod_nss handles authentication when a client presents a valid certificate. Rather than properly validating the certificate against the expected credentials, the module accepts any valid certificate when the user enters 'password' as the authentication credential. This design error creates a scenario where the system performs an incomplete validation check, allowing any certificate that has been properly issued and validated by the certificate authority to be accepted without proper verification of the associated password. The vulnerability stems from improper input validation and authentication flow logic, where the system fails to properly authenticate the user based on the certificate information rather than treating the certificate as a sufficient authentication mechanism on its own.
The operational impact of this vulnerability extends far beyond simple unauthorized access. Attackers can exploit this flaw to gain administrative privileges, access sensitive data, and potentially compromise entire server environments. The vulnerability affects web applications that rely on certificate-based authentication for user access control, making it particularly dangerous in enterprise environments where such authentication methods are commonly implemented. The consequences include potential data breaches, unauthorized system modifications, and complete compromise of services that depend on mod_nss for secure communication. This vulnerability essentially renders certificate-based authentication ineffective for these systems, as any valid certificate holder can bypass the password requirement and assume the identity of any user whose certificate they possess.
Organizations should immediately implement mitigation strategies that include updating to mod_nss versions that address this vulnerability, which typically involves upgrading to versions 1.0.9 or later where proper authentication validation has been implemented. Network administrators should also consider disabling certificate-based authentication methods until proper updates are applied, and implement additional monitoring to detect unauthorized access attempts. The vulnerability aligns with CWE-287, which addresses improper authentication issues, and represents a clear violation of the principle of least privilege in cybersecurity. From an ATT&CK framework perspective, this vulnerability maps to techniques involving privilege escalation and initial access through valid accounts, as attackers can effectively use legitimate certificates to gain unauthorized access to systems.
Security professionals should conduct comprehensive audits of all systems running mod_nss to identify vulnerable configurations and ensure proper certificate management practices are in place. The remediation process requires not only software updates but also verification that certificate authorities and trust relationships are properly maintained. Organizations should also implement additional layers of security including multi-factor authentication, network segmentation, and enhanced monitoring to detect potential exploitation attempts. This vulnerability demonstrates the critical importance of thorough security testing and validation of authentication mechanisms, particularly in cryptographic modules that handle sensitive access control functions. The incident underscores the need for regular security assessments and prompt patch management to prevent exploitation of known vulnerabilities in widely deployed security components.