CVE-2009-3765 in mutt
Summary
by MITRE
mutt_ssl.c in mutt 1.5.19 and 1.5.20, 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 • 08/24/2021
The vulnerability described in CVE-2009-3765 represents a critical security flaw in the mutt email client's SSL/TLS certificate validation mechanism. This issue specifically affects versions 1.5.19 and 1.5.20 of the mutt email client when configured to use OpenSSL for secure communications. The flaw resides in the mutt_ssl.c file which handles SSL certificate validation processes, creating a significant gap in the client's ability to properly verify server identities during secure connections.
The technical implementation of this vulnerability stems from improper handling of null characters within the Common Name field of X.509 certificates. When a certificate contains a null character within the subject's Common Name field, the mutt client fails to correctly process this character, leading to a bypass of the standard certificate validation procedures. This improper handling allows attackers to craft malicious certificates that appear valid to the mutt client while actually being issued by legitimate certificate authorities. The vulnerability specifically exploits the way the software processes certificate subject information, creating a path where an attacker can present a forged certificate that contains a null character in its Common Name field, thereby fooling the client into accepting it as legitimate.
The operational impact of this vulnerability is severe and directly enables man-in-the-middle attacks against users of the affected mutt versions. An attacker with access to a legitimate certificate authority's credentials or the ability to create certificates with null characters in their Common Name fields can successfully impersonate any legitimate SSL server. This compromises the integrity of secure email communications, potentially allowing attackers to intercept, modify, or redirect email traffic between users and their mail servers. The vulnerability essentially undermines the fundamental trust model of SSL/TLS certificates, making it possible for attackers to establish false secure connections that appear legitimate to the mutt client.
This vulnerability aligns with CWE-295, which addresses improper certificate validation, and represents a specific instance of certificate spoofing that enables authentication bypass attacks. From an ATT&CK framework perspective, this issue maps to T1573.001 (Reconnaissance: Network Sniffing) and T1573.002 (Reconnaissance: Network Traffic Capture) as attackers can leverage this vulnerability to capture and manipulate encrypted email communications. The flaw also connects to T1071.004 (Application Layer Protocol: DNS) and T1566.001 (Credential Access: Phishing) as it enables attackers to create convincing phishing scenarios by presenting fake but seemingly legitimate certificates. Organizations using affected mutt versions face significant risk of data breaches and eavesdropping attacks, particularly in environments where secure email communication is critical.
The recommended mitigations for this vulnerability include immediate upgrading to mutt versions that contain patches addressing the certificate validation issue, typically versions 1.5.21 and later. System administrators should also implement additional monitoring for suspicious certificate activity and consider deploying certificate pinning mechanisms where appropriate. The fix implemented by the mutt development team involved correcting the handling of null characters in certificate subject fields, ensuring that such characters are properly detected and rejected during the certificate validation process. Organizations should also review their certificate management practices and ensure that certificate authorities are properly configured to prevent the issuance of certificates containing null characters in subject fields. Regular security audits of email client configurations and certificate handling procedures are essential to prevent exploitation of similar vulnerabilities in other software components.