CVE-2015-2696 in Kerberos
Summary
by MITRE
lib/gssapi/krb5/iakerb.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 IAKERB 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-2015-2696 represents a critical flaw in the MIT Kerberos 5 implementation that affects the GSSAPI (Generic Security Services Application Program Interface) subsystem. This issue specifically impacts the iakerb.c component which handles the IAKERB (Initial Authentication with Kerberos) protocol extension used for establishing secure authentication contexts. The vulnerability exists in versions prior to 1.14 of the krb5 library and stems from improper handling of context handles during the gss_inquire_context function call, creating a scenario where malicious actors can exploit the system through crafted IAKERB packets.
The technical root cause of this vulnerability lies in the improper validation and handling of context identifiers within the Kerberos authentication framework. When a malformed IAKERB packet is received and processed by the gss_inquire_context function, the system attempts to dereference an incorrect pointer that was not properly initialized or validated. This mismanagement of context handles creates a condition where the application reads from an invalid memory location, leading to an immediate crash of the process. The flaw is classified as a buffer over-read or incorrect pointer dereference, which falls under CWE-476, and represents a classic example of improper handling of security context objects. The vulnerability demonstrates how seemingly innocuous protocol extensions can create critical security holes when proper input validation and context management are not implemented.
The operational impact of this vulnerability extends beyond simple denial of service, as it can be exploited by remote attackers to disrupt authentication services across networks relying on Kerberos. In environments where Kerberos is used for single sign-on, network authentication, or service access control, an attacker could leverage this vulnerability to repeatedly crash authentication daemons or services, effectively rendering them unavailable to legitimate users. The attack vector requires only the ability to send specially crafted IAKERB packets to the target system, making it particularly dangerous in networked environments where Kerberos services are exposed to untrusted networks. This vulnerability directly impacts the availability and reliability of Kerberos-based authentication infrastructure, potentially affecting large enterprise environments where Kerberos is extensively deployed.
Organizations should implement immediate mitigation strategies including updating to MIT Kerberos 5 version 1.14 or later, which contains the necessary patches to properly validate context handles during IAKERB processing. Network segmentation and access controls should be strengthened to limit exposure of Kerberos services to untrusted networks, while monitoring systems should be configured to detect anomalous IAKERB packet patterns. The vulnerability also highlights the importance of proper input validation in security-critical code paths and demonstrates how protocol implementations must carefully manage security contexts to prevent memory corruption vulnerabilities. From an ATT&CK perspective, this vulnerability maps to the privilege escalation and denial of service tactics, as it allows attackers to disrupt services and potentially gain unauthorized access to authentication systems, emphasizing the need for robust security testing and code review processes in cryptographic implementations.