CVE-2008-2809 in Firefox
Summary
by MITRE
Mozilla 1.9 M8 and earlier, Mozilla Firefox 2 before 2.0.0.15, SeaMonkey 1.1.5 and other versions before 1.1.10, Netscape 9.0, and other Mozilla-based web browsers, when a user accepts an SSL server certificate on the basis of the CN domain name in the DN field, regard the certificate as also accepted for all domain names in subjectAltName:dNSName fields, which makes it easier for remote attackers to trick a user into accepting an invalid certificate for a spoofed web site.
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Analysis
by VulDB Data Team • 03/16/2021
This vulnerability represents a critical certificate validation flaw in Mozilla-based web browsers that fundamentally undermines the security of SSL/TLS certificate verification processes. The issue affects a wide range of software including Mozilla Firefox versions prior to 2008, SeaMonkey versions before 1.1.10, and Netscape 9.0, creating a significant gap in the certificate trust model that could be exploited by malicious actors. The vulnerability specifically manifests when browsers accept an SSL server certificate based on the Common Name field within the certificate's distinguished name, erroneously extending that acceptance to all domain names listed in the subjectAltName extension's dNSName fields. This behavior violates fundamental principles of certificate validation and creates a dangerous precedent where users may believe they are connecting to a legitimate site when they are actually communicating with a spoofed entity.
The technical flaw stems from improper certificate validation logic that fails to properly distinguish between certificate fields during trust decisions. When a user manually accepts a certificate for a specific domain through the Common Name field, the browser incorrectly treats this acceptance as valid for all alternative names present in the subjectAltName extension. This creates a false sense of security where users may proceed with transactions or data exchanges believing they are communicating with a legitimate server, while in reality they are interacting with a malicious actor who has obtained a certificate for a different domain but is leveraging the user's initial certificate acceptance. The vulnerability is particularly dangerous because it operates at the user interaction level, making it difficult to detect through automated security tools and relying heavily on user behavior patterns.
The operational impact of this vulnerability extends far beyond simple certificate validation issues, creating potential for widespread man-in-the-middle attacks and credential theft across numerous web applications. Attackers can exploit this weakness by obtaining SSL certificates for domains that are likely to be trusted by users, such as common service domains or corporate intranet resources, and then using the flawed validation to deceive users into accepting certificates for completely different domains. This opens up possibilities for phishing attacks, data interception, and session hijacking across various web services that rely on SSL/TLS for security. The vulnerability affects the core trust mechanisms of web browsers and undermines the fundamental security model of public key infrastructure, making it particularly concerning for enterprise environments where users may be accessing sensitive corporate resources. According to CWE-295, this represents a weakness in certificate validation that directly impacts the integrity of the authentication process, while ATT&CK framework's T1071.001 technique demonstrates how such flaws can be leveraged for network protocol manipulation and credential harvesting.
Organizations and users must implement immediate mitigations including updating to patched versions of affected browsers, implementing additional certificate validation monitoring, and educating users about the importance of carefully reviewing certificate information before accepting any security warnings. The recommended approach involves deploying browser updates that correct the certificate validation logic to properly separate Common Name acceptance from subjectAltName field validation. Security teams should also consider implementing additional monitoring for certificate validation events and user acceptance patterns, as well as establishing clear policies for certificate management and user training on recognizing legitimate security warnings versus potential exploitation attempts. The vulnerability highlights the critical importance of maintaining up-to-date security software and underscores the need for comprehensive security awareness training to prevent users from inadvertently accepting malicious certificates that could compromise their security posture.