CVE-2009-3044 in Web Browser
Summary
by MITRE
Opera before 10.00 does not properly handle a (1) \0 character or (2) invalid wildcard 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.
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Analysis
by VulDB Data Team • 03/08/2025
The vulnerability described in CVE-2009-3044 represents a critical SSL/TLS certificate validation flaw in Opera web browsers prior to version 10.00. This issue stems from inadequate handling of special characters within the Common Name field of X.509 certificates, specifically involving null characters and invalid wildcard patterns. The vulnerability exists at the core of certificate trust validation mechanisms that Opera employs to establish secure connections with web servers. When a certificate contains a null character or malformed wildcard syntax in its subject CN field, Opera fails to properly validate the certificate against the domain name being accessed, creating a significant security gap that can be exploited by malicious actors.
The technical flaw manifests in Opera's certificate validation algorithm which does not adequately sanitize or reject certificates containing malformed characters in the Common Name field. A null character represented as in the description can be embedded within certificate subject names, while invalid wildcard characters may include patterns such as multiple consecutive asterisks or malformed domain wildcard syntax. These characters can bypass normal validation checks and allow an attacker to create a certificate that appears to be issued by a legitimate CA but contains a specially crafted subject name that matches the target domain. The vulnerability operates at the level of certificate subject validation and falls under CWE-295 which addresses improper certificate validation, specifically focusing on weaknesses in certificate chain validation and hostname verification processes.
This vulnerability enables man-in-the-middle attacks by allowing attackers to create fraudulent SSL certificates that can successfully validate against target domains. An attacker who can obtain a certificate from a legitimate CA with a specially crafted subject name containing the problematic characters can then intercept communications between users and legitimate servers. The impact extends beyond simple certificate validation failures to encompass complete trust model compromise, as users would be unable to distinguish between legitimate and malicious certificates when the certificate validation process fails to properly detect the forged certificate. The operational consequences include potential data interception, session hijacking, and credential theft across all HTTPS connections that rely on Opera's certificate validation.
The attack vector requires an attacker to first obtain a certificate from a legitimate CA, though this may be accomplished through various means including exploitation of CA vulnerabilities or social engineering techniques. Once the certificate is obtained, the attacker can craft a subject name containing null characters or invalid wildcards that will pass Opera's validation checks. The mitigation strategy involves updating to Opera version 10.00 or later, which includes proper certificate validation handling that rejects certificates with malformed characters in the subject CN field. Additionally, system administrators should implement certificate pinning where possible, monitor certificate issuance patterns for suspicious activity, and consider using certificate transparency mechanisms to detect unauthorized certificate issuance. This vulnerability aligns with ATT&CK technique T1552.001 which covers credentials from password storage and T1552.004 which addresses credentials in files, as the compromised trust model can lead to credential exposure during intercepted sessions. The issue also demonstrates the importance of proper input validation and sanitization in security-critical code paths, emphasizing the need for robust certificate validation libraries that properly handle edge cases in certificate subject formatting.