CVE-2011-4197 in pfSense
Summary
by MITRE
etc/inc/certs.inc in the PKI implementation in pfSense before 2.0.1 creates each X.509 certificate with a true value for the CA basic constraint, which allows remote attackers to create sub-certificates for arbitrary subjects by leveraging the private key.
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Analysis
by VulDB Data Team • 11/28/2021
The vulnerability identified as CVE-2011-4197 resides within the certificate management subsystem of pfSense, specifically in the file etc/inc/certs.inc within the PKI implementation. This flaw represents a critical security weakness that fundamentally undermines the certificate authority structure by improperly configuring the CA basic constraint extension in X.509 certificates. The issue affects pfSense versions prior to 2.0.1, making it a significant concern for organizations relying on this firewall and router platform for network security management.
The technical flaw stems from the improper implementation of the CA basic constraint extension within the X.509 certificate generation process. In standard PKI implementations, the CA basic constraint extension serves as a critical control mechanism that explicitly defines whether a certificate can function as a certificate authority. When this extension is set to true, it indicates that the certificate holder is authorized to issue subordinate certificates. However, in the affected pfSense versions, this constraint was incorrectly set to true for all certificates generated by the system, regardless of their intended role in the certificate hierarchy. This misconfiguration effectively transforms every certificate generated by the system into a potential certificate authority capable of issuing sub-certificates.
The operational impact of this vulnerability is severe and far-reaching within the context of network security infrastructure. Remote attackers who can access the pfSense system's certificate management capabilities can exploit this flaw to generate sub-certificates for arbitrary subjects, effectively bypassing the intended certificate hierarchy and trust model. This capability enables attackers to create fraudulent certificates that could be used for man-in-the-middle attacks, certificate forgery, or to establish unauthorized trust relationships within the network. The vulnerability directly violates the fundamental principle of certificate authority separation and can lead to complete compromise of the PKI infrastructure managed by pfSense. According to the CWE catalog, this represents a weakness categorized under CWE-310: Cryptographic Issues, specifically related to improper certificate handling and trust management.
The attack vector for this vulnerability is particularly concerning as it requires only remote access to the pfSense system's certificate management interface. Once an attacker gains access to the system, they can leverage the private key associated with the compromised certificate to generate additional certificates that appear legitimate within the trust chain. This attack pattern aligns with techniques described in the MITRE ATT&CK framework under the T1552 category for defense evasion and credential access. The vulnerability essentially provides attackers with the capability to perform certificate impersonation and trust exploitation at scale, potentially compromising all systems that rely on certificates issued by the affected pfSense system.
Organizations should implement immediate mitigations including upgrading to pfSense version 2.0.1 or later, which contains the necessary patches to correct the certificate generation logic. Additionally, administrators should conduct thorough certificate audits to identify and revoke any certificates that may have been compromised through this vulnerability. The mitigation strategy should also include monitoring for unauthorized certificate creation activities and implementing stricter access controls for certificate management functions. Security teams should also consider implementing certificate transparency measures and enhanced logging of certificate-related activities to detect potential exploitation attempts. The vulnerability demonstrates the critical importance of proper certificate authority configuration and highlights the need for regular security assessments of PKI implementations within network infrastructure platforms.