CVE-2009-2417 in cURL
Summary
by MITRE
lib/ssluse.c in cURL and libcurl 7.4 through 7.19.5, when OpenSSL is used, does not properly handle a \0 character 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, a related issue to CVE-2009-2408.
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Analysis
by VulDB Data Team • 03/18/2019
The vulnerability described in CVE-2009-2417 represents a critical security flaw in the cURL and libcurl libraries that affects SSL/TLS certificate validation processes when OpenSSL is utilized. This issue specifically targets the handling of domain names within the Common Name field of X.509 certificates, creating a pathway for sophisticated man-in-the-middle attacks that can compromise secure communications. The vulnerability exists in versions 7.4 through 7.19.5 of the cURL library, making a substantial portion of widely deployed applications susceptible to this attack vector.
The technical flaw stems from improper handling of null characters within the subject's Common Name field of SSL certificates. When a certificate contains a null character within the domain name portion of the CN field, the cURL library fails to properly validate the certificate against the expected hostname during SSL/TLS handshakes. This parsing error occurs during the certificate verification phase where the library should strictly enforce hostname matching according to RFC standards. The null character injection allows attackers to craft certificates that appear valid to the cURL library while actually containing malicious domain names, effectively bypassing the certificate validation mechanism that is fundamental to SSL/TLS security.
The operational impact of this vulnerability is severe as it enables attackers to perform successful man-in-the-middle attacks against systems using affected cURL versions. An attacker with access to a legitimate Certification Authority's certificate can inject a null character into the domain name, creating a certificate that will be accepted by vulnerable applications while still appearing to be from a trusted authority. This allows the attacker to intercept and potentially modify encrypted communications between clients and servers, undermining the entire SSL/TLS security model that users rely upon for secure data transmission. The vulnerability directly relates to CWE-295 which addresses improper certificate validation and aligns with ATT&CK technique T1041 which covers data from network connections.
Systems and applications using cURL versions between 7.4 and 7.19.5 are at significant risk, particularly those handling sensitive data transfers such as financial transactions, personal information exchanges, and secure communications. The vulnerability affects not just standalone cURL applications but also any software that depends on libcurl for SSL/TLS functionality, including web browsers, email clients, and various network utilities. Organizations utilizing affected versions should immediately implement mitigation strategies including updating to patched versions of cURL and libcurl, implementing additional certificate validation layers, and monitoring network traffic for suspicious certificate usage patterns. The issue demonstrates the critical importance of proper input validation in cryptographic libraries and highlights how seemingly minor parsing flaws can have devastating security implications for the entire internet infrastructure.