CVE-2010-0433 in OpenSSL
Summary
by MITRE
The kssl_keytab_is_available function in ssl/kssl.c in OpenSSL before 0.9.8n, when Kerberos is enabled but Kerberos configuration files cannot be opened, does not check a certain return value, which allows remote attackers to cause a denial of service (NULL pointer dereference and daemon crash) via SSL cipher negotiation, as demonstrated by a chroot installation of Dovecot or stunnel without Kerberos configuration files inside the chroot.
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Analysis
by VulDB Data Team • 05/01/2026
The vulnerability described in CVE-2010-0433 represents a critical denial of service flaw within the OpenSSL cryptographic library that specifically impacts systems utilizing Kerberos authentication mechanisms. This issue affects OpenSSL versions prior to 0.9.8n and manifests when the kssl_keytab_is_available function fails to properly validate return values during Kerberos configuration file access attempts. The flaw occurs in the ssl/kssl.c source file, which handles Kerberos security layer operations within the SSL/TLS implementation. When Kerberos is enabled but the necessary configuration files cannot be accessed - such as in chroot environments where these files are not present - the function proceeds without proper error handling, creating a dangerous condition that can be exploited by remote attackers.
The technical exploitation of this vulnerability relies on manipulating SSL cipher negotiation processes to trigger the problematic code path. When OpenSSL attempts to establish an SSL connection and encounters a Kerberos-enabled configuration where required files are inaccessible, the kssl_keytab_is_available function fails to properly check return values from underlying Kerberos operations. This oversight leads to a NULL pointer dereference condition, where the application attempts to access memory at address zero, causing the daemon process to crash and terminate unexpectedly. The vulnerability is particularly dangerous in server environments where continuous availability is critical, as the crash can be triggered remotely without requiring authentication or special privileges. The specific scenario described involves chroot installations of services like Dovecot or stunnel, where the chroot environment lacks the necessary Kerberos configuration files, creating the perfect conditions for exploitation.
The operational impact of this vulnerability extends beyond simple service disruption to potentially compromise system availability and integrity in production environments. When exploited, the vulnerability can cause cascading failures in services that depend on OpenSSL for secure communications, particularly affecting mail servers, web servers, and other network services that utilize SSL/TLS with Kerberos authentication. The attack vector is particularly concerning because it requires no authentication and can be executed over standard network connections during normal SSL handshake procedures. This makes it an attractive target for attackers seeking to disrupt services without requiring insider knowledge or elevated privileges. The vulnerability aligns with CWE-476 which describes NULL pointer dereference conditions, and represents a classic example of inadequate error handling in security-critical code paths.
Mitigation strategies for this vulnerability primarily focus on immediate patching of affected OpenSSL installations to version 0.9.8n or later, where the return value checking has been properly implemented. System administrators should also implement proper Kerberos configuration file management, ensuring that required Kerberos files are available in chroot environments when Kerberos authentication is enabled. Network segmentation and monitoring solutions can help detect unusual SSL handshake patterns that might indicate exploitation attempts. Additionally, implementing proper service restart mechanisms and failover procedures can minimize the impact of successful attacks. From an ATT&CK framework perspective, this vulnerability maps to the T1499.004 technique related to network denial of service and represents a weakness in the software development lifecycle that could be addressed through improved code review processes and comprehensive testing of error handling scenarios. Organizations should also consider implementing intrusion detection systems that can identify and alert on anomalous SSL connection patterns that might indicate exploitation attempts.