CVE-2015-0681 in IOS XE
Summary
by MITRE
The TFTP server in Cisco IOS 12.2(44)SQ1, 12.2(33)XN1, 12.4(25e)JAM1, 12.4(25e)JAO5m, 12.4(23)JY, 15.0(2)ED1, 15.0(2)EY3, 15.1(3)SVF4a, and 15.2(2)JB1 and IOS XE 2.5.x, 2.6.x, 3.1.xS, 3.2.xS, 3.3.xS, 3.4.xS, and 3.5.xS before 3.6.0S; 3.1.xSG, 3.2.xSG, and 3.3.xSG before 3.4.0SG; 3.2.xSE before 3.3.0SE; 3.2.xXO before 3.3.0XO; 3.2.xSQ; 3.3.xSQ; and 3.4.xSQ allows remote attackers to cause a denial of service (device hang or reload) via multiple requests that trigger improper memory management, aka Bug ID CSCts66733.
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Analysis
by VulDB Data Team • 12/02/2024
The vulnerability described in CVE-2015-0681 represents a critical denial of service flaw within Cisco IOS and IOS XE operating systems that affects multiple software versions across different release branches. This issue specifically targets the Trivial File Transfer Protocol (TFTP) server implementation, which is a fundamental network service used for transferring files between network devices and servers. The vulnerability manifests when the TFTP server receives multiple malicious requests that exploit improper memory management mechanisms within the IOS kernel. According to the Cisco bug ID CSCts66733, this flaw was particularly concerning because it could cause complete device hang or forced reloads, effectively rendering network infrastructure unavailable to legitimate users and administrators.
The technical root cause of this vulnerability lies in the insufficient memory management practices within the TFTP server component of affected Cisco IOS versions. When multiple concurrent requests are processed, the system fails to properly handle memory allocation and deallocation cycles, leading to memory corruption or exhaustion conditions that ultimately result in system instability. This type of vulnerability falls under CWE-129, which describes improper validation of array index values, and more specifically aligns with CWE-125, which covers out-of-bounds read conditions. The flaw demonstrates poor resource management practices that allow attackers to exploit the memory handling mechanisms through carefully crafted sequences of TFTP requests, making it particularly dangerous in network environments where TFTP services are actively used for firmware updates, configuration transfers, or other administrative functions.
From an operational perspective, this vulnerability poses significant risks to network availability and business continuity. The ability to remotely trigger device hangs or reloads through simple TFTP requests means that an attacker with minimal privileges could disrupt network operations, potentially causing cascading failures throughout connected infrastructure. Network administrators who rely on TFTP for routine maintenance tasks would face potential service interruptions, while the vulnerability's exploitation could occur without authentication, making it particularly attractive to malicious actors seeking to disrupt operations. This aligns with ATT&CK technique T1499.004, which covers network denial of service attacks, and demonstrates how seemingly benign network protocols can be weaponized to create substantial operational impact.
The mitigation strategies for this vulnerability require immediate attention from network administrators and security teams. The primary recommendation involves upgrading affected IOS and IOS XE versions to patched releases, particularly those mentioned in the CVE description that are not vulnerable to this specific flaw. Organizations should also consider implementing network segmentation to limit access to TFTP services, disabling unnecessary TFTP server functionality, and monitoring for unusual TFTP traffic patterns that might indicate exploitation attempts. Additionally, implementing network access controls and firewall rules to restrict TFTP server access to trusted network segments can help reduce the attack surface. The vulnerability's classification as a denial of service issue also suggests that implementing redundant network paths and failover mechanisms could help maintain service availability during potential exploitation attempts, while regular security assessments should be conducted to identify and remediate similar memory management flaws in other network services.