CVE-2014-3504 in Subversion
Summary
by MITRE
The (1) serf_ssl_cert_issuer, (2) serf_ssl_cert_subject, and (3) serf_ssl_cert_certificate functions in Serf 0.2.0 through 1.3.x before 1.3.7 does not properly handle a NUL byte in a domain name in the subject s Common Name (CN) field of an X.509 certificate, which allows man-in-the-middle attackers to spoof arbitrary SSL servers via a crafted certificate issued by a legitimate Certification Authority.
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Analysis
by VulDB Data Team • 03/28/2022
The vulnerability described in CVE-2014-3504 affects the Serf library version 0.2.0 through 1.3.x before 1.3.7, specifically targeting three functions responsible for SSL certificate validation: serf_ssl_cert_issuer, serf_ssl_cert_subject, and serf_ssl_cert_certificate. This issue represents a critical security flaw in the certificate processing logic that undermines the fundamental trust model of SSL/TLS communications. The vulnerability stems from improper handling of null bytes within the Common Name field of X.509 certificates, creating a pathway for attackers to bypass certificate validation mechanisms through carefully crafted malicious certificates.
The technical flaw manifests when a certificate contains a null byte within the subject's Common Name field, which the affected Serf functions fail to properly process or reject. This improper handling allows an attacker to construct a certificate where the null byte effectively terminates the string processing, causing the system to only validate against the portion of the domain name preceding the null byte. This creates a dangerous scenario where a certificate issued for one domain could be used to impersonate another domain, particularly when the null byte placement results in a valid subdomain match. The vulnerability operates at the SSL/TLS certificate validation layer, where the certificate's subject information should be rigorously verified against the target server's hostname to prevent man-in-the-middle attacks.
The operational impact of this vulnerability is severe as it directly enables man-in-the-middle attacks by allowing attackers to spoof arbitrary SSL servers. An attacker with access to a legitimate Certification Authority's certificate signing capabilities could generate a malicious certificate containing a null byte in the Common Name field, thereby bypassing the normal certificate validation procedures. This would permit the attacker to establish seemingly legitimate SSL connections to unsuspecting clients, potentially intercepting sensitive communications, performing credential harvesting, or executing other malicious activities. The vulnerability affects any system using Serf library versions within the affected range, making it particularly dangerous for distributed systems, service discovery mechanisms, and any application relying on secure SSL communications for service-to-service interactions.
The vulnerability maps to CWE-170, which specifically addresses improper handling of null bytes in strings, and aligns with ATT&CK technique T1573.002 for "Tunneling through Secure Shell (SSH)" and T1041 for "Exfiltration Over C2 Channel" as it enables attackers to establish unauthorized secure connections. Organizations should immediately upgrade to Serf version 1.3.7 or later to remediate this vulnerability, while also implementing additional monitoring for suspicious certificate validation behaviors. Network administrators should consider implementing certificate pinning mechanisms and enhanced certificate monitoring to detect potential exploitation attempts. The fix implemented in version 1.3.7 involves proper null byte validation within certificate subject fields, ensuring that such characters are either rejected or properly handled during certificate parsing and validation processes to maintain the integrity of SSL/TLS certificate verification mechanisms.