CVE-2010-1192 in libESMTP
Summary
by MITRE
libESMTP, probably 1.0.4 and earlier, 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.
If you want to get the best quality for vulnerability data then you always have to consider VulDB.
Analysis
by VulDB Data Team • 05/04/2026
The vulnerability described in CVE-2010-1192 affects libESMTP version 1.0.4 and earlier, representing a critical flaw in SSL/TLS certificate validation mechanisms. This issue specifically targets the handling of domain names within the Common Name field of X.509 certificates, where the presence of a null character can be exploited to bypass security checks. The vulnerability stems from insufficient input validation in the certificate subject parsing routine, allowing malicious actors to craft certificates that appear legitimate while actually containing malformed domain specifications. This weakness creates a pathway for attackers to perform man-in-the-middle attacks by presenting certificates that would otherwise be rejected by proper validation procedures.
The technical exploitation of this vulnerability occurs when libESMTP processes SSL certificates containing a null character within the domain name portion of the Common Name field. During certificate validation, the application fails to properly sanitize or reject such malformed entries, causing the system to incorrectly interpret the certificate subject and potentially accept fraudulent certificates. The null character acts as a delimiter or terminator that disrupts normal string processing, leading to improper certificate validation outcomes. This flaw directly relates to CWE-20, "Improper Input Validation," and demonstrates how seemingly minor input handling issues can create significant security vulnerabilities in cryptographic validation systems.
The operational impact of CVE-2010-1192 is substantial, as it enables attackers to conduct successful man-in-the-middle attacks against SSL/TLS connections. An attacker with access to a legitimate Certification Authority's certificate signing capabilities can generate certificates that appear valid to vulnerable libESMTP implementations, allowing them to intercept and potentially modify communications between clients and servers. This vulnerability undermines the fundamental trust model of SSL/TLS encryption, as it permits certificate spoofing without requiring the attacker to compromise the CA infrastructure directly. The attack vector is particularly dangerous because it can be executed against any system using the vulnerable libESMTP library, affecting email servers, web applications, and other services that rely on proper SSL certificate validation.
Organizations affected by this vulnerability should prioritize immediate patching of all systems running libESMTP version 1.0.4 or earlier, with the recommended solution being an upgrade to version 1.0.5 or later where the null character handling issue has been resolved. System administrators should also implement additional monitoring for suspicious certificate validation events and consider deploying certificate pinning mechanisms as a defense-in-depth strategy. The vulnerability aligns with ATT&CK technique T1552.001, "Unsecured Credentials," and T1046, "Network Service Scanning," as it enables attackers to establish unauthorized communication channels and potentially escalate privileges through compromised encrypted connections. Regular security audits should verify that all SSL/TLS implementations properly handle edge cases in certificate subject parsing, particularly around null character and special character handling in domain name fields.