CVE-2009-2408 in SeaMonkey
Summary
by MITRE
Mozilla Network Security Services (NSS) before 3.12.3, Firefox before 3.0.13, Thunderbird before 2.0.0.23, and SeaMonkey before 1.1.18 do 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. NOTE: this was originally reported for Firefox before 3.5.
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Analysis
by VulDB Data Team • 08/13/2021
The vulnerability described in CVE-2009-2408 represents a critical flaw in the handling of X.509 certificate validation within Mozilla Network Security Services and related browser applications. This issue specifically affects the processing of domain names contained within the Common Name field of SSL certificates, where the presence of a null character in the certificate subject's CN field creates a dangerous validation bypass. The vulnerability stems from improper string handling mechanisms that fail to properly sanitize or reject certificates containing null characters, allowing attackers to craft malicious certificates that appear legitimate to vulnerable systems. This flaw enables man-in-the-middle attacks by permitting attackers to spoof arbitrary SSL servers through certificates issued by legitimate Certification Authorities, effectively undermining the entire public key infrastructure trust model.
The technical root cause of this vulnerability lies in the insufficient validation of certificate subject fields, particularly the Common Name field where domain names are typically stored. When a certificate contains a null character within the CN field, the vulnerable NSS implementation fails to properly process this malformed input, leading to inconsistent certificate validation behavior. The null character creates a parsing anomaly that allows the certificate validation logic to accept a certificate with a domain name containing this character as valid, even though such certificates should be rejected during standard certificate chain validation. This parsing failure occurs at the certificate validation layer where the system should enforce strict validation rules against malformed certificate data. The vulnerability manifests when the certificate verification process does not properly handle the null character, causing the system to potentially accept certificates that would otherwise be rejected due to their malformed nature, thereby creating a trust boundary violation.
The operational impact of this vulnerability extends far beyond simple certificate validation failures, as it fundamentally compromises the security of SSL/TLS communications. Attackers can exploit this weakness by obtaining a legitimate certificate from a trusted Certification Authority and then modifying the Common Name field to include a null character, creating a certificate that appears valid to vulnerable systems while actually allowing the attacker to impersonate any domain. This creates a severe risk for web browsing, email security, and any other SSL/TLS protected communications where users expect to be protected from man-in-the-middle attacks. The vulnerability affects multiple Mozilla products including Firefox, Thunderbird, and SeaMonkey, indicating a widespread impact across the Mozilla ecosystem. Organizations relying on these applications for secure communications face significant risk, as the vulnerability can be exploited without requiring special privileges or advanced technical skills, making it particularly dangerous in enterprise environments where SSL/TLS security is critical for protecting sensitive data.
The mitigation strategy for this vulnerability requires immediate patching of affected software versions, with the most effective solution being the upgrade to patched versions of Mozilla Network Security Services, Firefox, Thunderbird, and SeaMonkey. System administrators should prioritize updating all affected applications to versions that properly handle null characters in certificate subject fields, as the vulnerability cannot be effectively mitigated through configuration changes alone. Organizations should also implement certificate monitoring systems to detect and alert on potentially malicious certificates that may exploit this vulnerability. Security teams should conduct thorough vulnerability assessments of their environments to identify all instances of affected software and ensure complete remediation. This vulnerability aligns with CWE-20, which describes improper input validation, and represents a clear violation of the principle of least privilege in certificate validation, where the system should reject malformed certificates rather than attempting to process them. From an ATT&CK perspective, this vulnerability maps to T1573.001 for secure channel protocols and T1071.001 for application layer protocols, as it enables attackers to manipulate secure communications through certificate manipulation and man-in-the-middle attacks. The vulnerability also demonstrates characteristics of T1566.001 for credential access through social engineering and T1190 for exploitation of remote services, as attackers can leverage this weakness to gain unauthorized access to secure communications channels.