CVE-2009-0845 in Solaris
Summary
by MITRE
The spnego_gss_accept_sec_context function in lib/gssapi/spnego/spnego_mech.c in MIT Kerberos 5 (aka krb5) 1.5 through 1.6.3, when SPNEGO is used, allows remote attackers to cause a denial of service (NULL pointer dereference and daemon crash) via invalid ContextFlags data in the reqFlags field in a negTokenInit token.
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Analysis
by VulDB Data Team • 12/29/2024
The vulnerability described in CVE-2009-0845 represents a critical denial of service weakness within the MIT Kerberos 5 authentication system that affects versions 1.5 through 1.6.3. This flaw specifically targets the spnego_gss_accept_sec_context function which handles SPNEGO (Simple and Protected GSSAPI Negotiation Mechanism) token processing. The vulnerability arises from insufficient input validation when processing negTokenInit tokens, which are part of the GSSAPI negotiation process used to establish secure communication between clients and servers. The affected component operates within the lib/gssapi/spnego/spnego_mech.c file, making it a core element of the Kerberos authentication infrastructure that handles security context establishment for network services.
The technical implementation of this vulnerability stems from a NULL pointer dereference condition that occurs when the spnego_gss_accept_sec_context function processes malformed ContextFlags data within the reqFlags field of negTokenInit tokens. When remote attackers craft specially formatted tokens containing invalid or malformed ContextFlags values, the function fails to properly validate these inputs before attempting to dereference pointers that may be NULL. This particular weakness falls under CWE-476 which specifically addresses NULL pointer dereference vulnerabilities, where the application attempts to access memory through a pointer that has not been properly initialized or validated. The flaw demonstrates poor input sanitization practices in the GSSAPI negotiation layer where the system assumes valid token structures without proper verification of field contents.
The operational impact of this vulnerability is significant as it enables remote attackers to cause complete daemon crashes and system-wide denial of service conditions. When the vulnerable MIT Kerberos 5 daemon processes the malicious negTokenInit token, the NULL pointer dereference results in an immediate crash of the authentication service, rendering the system unable to process legitimate authentication requests. This creates a cascading effect that can disrupt network services relying on Kerberos authentication, potentially affecting email servers, file sharing services, database access, and other networked applications that depend on secure authentication mechanisms. The vulnerability is particularly dangerous because it can be exploited remotely without requiring authentication credentials, making it an attractive target for attackers seeking to disrupt services. According to ATT&CK framework, this represents a privilege escalation and denial of service technique that can be categorized under T1499 which covers network disruption and service availability attacks.
Mitigation strategies for this vulnerability require immediate patching of affected MIT Kerberos 5 installations to versions 1.6.4 or later where the input validation has been corrected. System administrators should also implement network monitoring to detect unusual authentication token patterns that may indicate exploitation attempts. Additional defensive measures include configuring firewalls to limit access to Kerberos services, implementing intrusion detection systems that can identify malformed GSSAPI tokens, and establishing robust logging mechanisms to track authentication attempts. The fix typically involves adding proper validation checks for the reqFlags field in negTokenInit tokens before any pointer dereference operations occur, ensuring that all input data is properly sanitized and validated according to GSSAPI specification requirements. Organizations should also consider implementing redundant authentication mechanisms and maintaining backup authentication services to minimize the impact of potential exploitation attempts.