CVE-2009-2973 in Chrome
Summary
by MITRE
Google Chrome before 2.0.172.43 does not prevent SSL connections to a site with an X.509 certificate signed with the (1) MD2 or (2) MD4 algorithm, which makes it easier for man-in-the-middle attackers to spoof arbitrary HTTPS servers via a crafted certificate, a related issue to CVE-2009-2409.
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Analysis
by VulDB Data Team • 08/20/2021
The vulnerability identified as CVE-2009-2973 represents a critical weakness in Google Chrome's SSL/TLS certificate validation mechanism prior to version 2.0.172.43. This flaw specifically addresses the browser's failure to properly reject certificates signed with weak cryptographic algorithms, namely MD2 and MD4 hashing functions. The vulnerability stems from Chrome's insufficient certificate validation logic that allowed connections to proceed even when the server presented certificates using these deprecated and cryptographically insecure algorithms. The issue directly impacts the fundamental security promise of HTTPS by creating a pathway for attackers to establish fraudulent secure connections that appear legitimate to users.
The technical root cause of this vulnerability lies in the browser's certificate validation process which did not adequately enforce cryptographic strength requirements for SSL certificates. When Chrome encountered certificates signed with MD2 or MD4 algorithms, it failed to reject them outright, instead allowing the connection to proceed. This behavior creates a significant attack surface because both MD2 and MD4 are known to be vulnerable to collision attacks, making it computationally feasible for attackers to generate fake certificates that would appear valid to the browser. The vulnerability operates at the TLS/SSL protocol layer and specifically targets the certificate verification phase where the browser should enforce minimum cryptographic standards. According to CWE-327, this represents a weakness in the use of a broken cryptographic algorithm, while the ATT&CK framework categorizes this under T1552.001 for credential access through manipulation of authentication tokens.
The operational impact of this vulnerability is severe as it enables man-in-the-middle attacks where attackers can impersonate legitimate websites by generating certificates using the MD2 or MD4 algorithms. Attackers exploiting this vulnerability can create fraudulent HTTPS connections that appear secure to users, potentially leading to credential theft, data interception, and other malicious activities. The vulnerability is particularly dangerous because it operates silently without user notification, making it difficult to detect compromised connections. Users connecting to websites that have been compromised or where attackers have obtained valid certificates using these weak algorithms will unknowingly establish insecure connections, undermining the trust model that HTTPS is designed to provide. This vulnerability directly relates to CVE-2009-2409, which addressed similar issues with weak cryptographic algorithms in SSL/TLS implementations, highlighting a broader pattern of insufficient cryptographic validation in web browsers of that era.
The mitigation for this vulnerability required updating Google Chrome to version 2.0.172.43 or later, which implemented proper certificate validation that rejects certificates signed with MD2 or MD4 algorithms. System administrators should ensure all browsers are updated to versions that properly enforce cryptographic strength requirements. Additionally, organizations should monitor for certificate usage of deprecated algorithms and implement certificate monitoring systems to detect any attempts to use weak cryptographic signatures. The fix addresses the core issue by strengthening the certificate validation logic to explicitly reject certificates using these insecure hashing algorithms, thereby restoring the integrity of the SSL/TLS security model. This vulnerability demonstrates the critical importance of maintaining up-to-date cryptographic standards and proper certificate validation practices in web browsers and security applications.