CVE-2011-4720 in TFTP Server
Summary
by MITRE
Hillstone HS TFTP Server 1.3.2 allows remote attackers to cause a denial of service (daemon crash) via a long filename in a (1) RRQ or (2) WRQ operation.
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Analysis
by VulDB Data Team • 02/27/2025
The vulnerability identified as CVE-2011-4720 affects Hillstone HS TFTP Server version 1.3.2 and represents a classic buffer overflow condition that can be exploited to cause a denial of service attack. This issue specifically manifests when the server processes Read Request (RRQ) or Write Request (WRQ) operations with excessively long filenames, leading to daemon instability and potential system crash. The vulnerability stems from insufficient input validation and bounds checking within the TFTP server implementation, where the software fails to properly handle filename lengths that exceed predetermined limits.
The technical flaw resides in the server's handling of network-based TFTP operations where client requests are processed without adequate sanitization of filename parameters. When an attacker sends a RRQ or WRQ packet containing a filename that surpasses the allocated buffer space, the server's memory management routines become corrupted, resulting in abrupt termination of the TFTP daemon service. This behavior aligns with CWE-121, which describes stack-based buffer overflow conditions, and CWE-122, which addresses heap-based buffer overflow scenarios, as the vulnerability can potentially affect both stack and heap memory regions depending on implementation details.
From an operational perspective, this vulnerability presents significant risks to network infrastructure security as TFTP servers are commonly used for network booting, firmware updates, and configuration file transfers in enterprise environments. The denial of service impact can disrupt critical network operations, particularly in scenarios where network devices rely on TFTP for automated provisioning and maintenance tasks. Attackers can exploit this weakness with minimal technical expertise by simply crafting malicious TFTP requests with oversized filenames, making it an attractive target for both casual attackers and more sophisticated threat actors seeking to disrupt network services.
The vulnerability's exploitability is enhanced by the fact that TFTP operates on a simple protocol that does not require authentication, making it accessible to any network entity capable of sending UDP packets to the affected server. This characteristic places the vulnerability in the ATT&CK framework under the T1190 category for Exploit Public-Facing Application, as it represents an attack vector that targets network services exposed to external networks. The impact extends beyond simple service disruption to potentially compromise network availability and operational continuity, particularly in environments where TFTP services are integral to network device management and provisioning workflows.
Mitigation strategies should focus on immediate patching of the affected Hillstone HS TFTP Server software to version 1.3.3 or later, which contains the necessary buffer overflow protections. Network administrators should also implement firewall rules to restrict TFTP service access to trusted networks only, and consider disabling TFTP services entirely if they are not required for network operations. Additional protective measures include implementing network monitoring to detect unusual TFTP traffic patterns and establishing proper input validation controls that limit filename lengths to prevent buffer overflow conditions. Organizations should also conduct regular vulnerability assessments to identify and remediate similar issues in other network services that may be susceptible to similar buffer overflow attacks, following best practices outlined in NIST SP 800-45 and other security frameworks for secure network service implementation.