CVE-2015-2695 in Kerberos
Summary
by MITRE
lib/gssapi/spnego/spnego_mech.c in MIT Kerberos 5 (aka krb5) before 1.14 relies on an inappropriate context handle, which allows remote attackers to cause a denial of service (incorrect pointer read and process crash) via a crafted SPNEGO packet that is mishandled during a gss_inquire_context call.
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Analysis
by VulDB Data Team • 06/26/2022
The vulnerability described in CVE-2015-2695 represents a critical security flaw within the MIT Kerberos 5 implementation that affects versions prior to 1.14. This issue resides in the spnego_mech.c file within the gssapi/spnego module, which is responsible for handling Simple and Protected GSSAPI Negotiation Mechanism operations. The flaw manifests when the system processes crafted SPNEGO packets during gss_inquire_context function calls, creating a scenario where improper context handle management leads to memory corruption and system instability. The vulnerability specifically targets the way Kerberos handles security context information during authentication negotiations, making it particularly dangerous in environments where Kerberos-based authentication is extensively used.
The technical root cause of this vulnerability stems from an inappropriate context handle reference that occurs during SPNEGO packet processing. When a maliciously crafted packet is received and processed through the gss_inquire_context call, the system attempts to access memory locations using an invalid or improperly initialized context handle. This mismanagement results in incorrect pointer reads that cause the application to crash or behave unpredictably. The flaw operates at the intersection of several security domains including authentication protocols, memory management, and network security mechanisms. According to CWE classification, this vulnerability maps to CWE-476 which describes NULL pointer dereference conditions, though the specific implementation involves improper context handling rather than simple null references.
From an operational impact perspective, this vulnerability enables remote attackers to execute denial of service attacks against Kerberos services without requiring any authentication credentials or privileged access. The attack can be executed over the network by sending specially crafted SPNEGO packets to any system running vulnerable versions of MIT Kerberos 5. The consequences extend beyond simple service disruption as the process crashes can be exploited to cause cascading failures in authentication infrastructure, particularly in environments where Kerberos is used as a central authentication mechanism for enterprise systems, file servers, and network services. The vulnerability's impact is amplified in large-scale deployments where a single compromised service could potentially affect multiple authenticated systems.
Security professionals should implement immediate mitigations including upgrading to MIT Kerberos 5 version 1.14 or later, which contains the necessary patches to address the context handle management issue. Organizations should also consider implementing network segmentation and monitoring to detect anomalous SPNEGO packet traffic patterns that might indicate exploitation attempts. The ATT&CK framework categorizes this vulnerability under T1499 which covers network denial of service attacks, while the specific exploitation technique aligns with T1071.3 for application layer protocol usage. Additional defensive measures include implementing intrusion detection systems that can identify malformed SPNEGO packets and configuring firewalls to limit unnecessary Kerberos service exposure. The vulnerability demonstrates the critical importance of proper memory management and context validation in security protocol implementations, as inadequate handling of authentication context information can lead to complete service compromise and denial of critical enterprise authentication infrastructure.