CVE-2000-0486 in TACACS+
Summary
by MITRE
Buffer overflow in Cisco TACACS+ tac_plus server allows remote attackers to cause a denial of service via a malformed packet with a long length field.
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Analysis
by VulDB Data Team • 04/21/2026
The vulnerability identified as CVE-2000-0486 represents a critical buffer overflow flaw within Cisco's TACACS+ tac_plus server implementation. This issue resides in the authentication and authorization service that operates on port 49 and is widely deployed across enterprise networks for managing access to network devices. The flaw manifests when the server processes incoming packets that contain an excessively long length field, causing the application to write beyond allocated memory boundaries. This buffer overflow condition occurs during the parsing of authentication packets, specifically when the server attempts to validate packet headers without proper bounds checking on the length field. The vulnerability stems from inadequate input validation mechanisms within the TACACS+ protocol implementation, where the system fails to properly sanitize or limit the size of incoming data structures before processing them.
The operational impact of this vulnerability extends beyond simple denial of service conditions, as it represents a fundamental security weakness that can be exploited by remote attackers without requiring authentication credentials. When an attacker crafts a malicious packet with an oversized length field, the tac_plus server experiences memory corruption that typically results in application crashes and subsequent service disruption. This creates a reliable denial of service scenario that can be executed repeatedly, potentially leading to extended network outages and unauthorized access to critical network infrastructure. The vulnerability directly maps to CWE-121, which describes heap-based buffer overflow conditions, and aligns with ATT&CK technique T1499.1 for network denial of service attacks. The attack surface is particularly concerning given that TACACS+ servers often operate as critical network services that authenticate administrators and users across multiple devices, making any disruption of these services potentially catastrophic for network operations and security posture.
Mitigation strategies for CVE-2000-0486 require immediate implementation of both network-level and application-level controls to prevent exploitation. Organizations should deploy network access control lists to restrict access to TACACS+ ports, limiting connectivity to trusted administrative networks only, while also implementing intrusion detection systems capable of identifying malformed packet patterns. Cisco released patches for this vulnerability in subsequent software updates, and system administrators must ensure all tac_plus implementations are updated to versions that include proper input validation and bounds checking mechanisms. Additional defensive measures include implementing network segmentation to isolate TACACS+ servers from general network traffic, deploying redundant authentication services to minimize single points of failure, and establishing robust monitoring protocols to detect unusual traffic patterns that may indicate exploitation attempts. The vulnerability demonstrates the importance of input validation in network services and serves as a reminder that authentication systems, while critical for security, can themselves become attack vectors when not properly secured against buffer overflow conditions.