CVE-2015-0661 in IOS XR
Summary
by MITRE
The SNMPv2 implementation in Cisco IOS XR allows remote authenticated users to cause a denial of service (snmpd daemon reload) via a malformed SNMP packet, aka Bug ID CSCur25858.
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Analysis
by VulDB Data Team • 04/15/2018
The vulnerability identified as CVE-2015-0661 represents a significant security flaw within Cisco IOS XR operating systems that impacts the SNMPv2 implementation. This issue specifically affects the snmpd daemon which is responsible for handling SNMP protocol communications within the network infrastructure. The vulnerability manifests when the system receives malformed SNMP packets from authenticated remote users, leading to an unexpected daemon reload that results in denial of service conditions. The bug was catalogued under Cisco's internal tracking system as CSCur25858, indicating its classification as a medium to high severity issue requiring immediate attention from network administrators and security teams.
The technical root cause of this vulnerability stems from inadequate input validation within the SNMPv2 processing module of IOS XR. When the snmpd daemon encounters malformed SNMP packets containing specially crafted data structures or malformed SNMP protocol elements, the system fails to properly handle these invalid inputs. This processing failure triggers an internal error condition that causes the snmpd daemon to restart automatically, effectively disrupting SNMP monitoring and management capabilities across the affected network devices. The vulnerability specifically exploits the lack of proper bounds checking and protocol validation mechanisms that should normally prevent malformed data from causing system instability. This type of flaw falls under CWE-129, Input Validation, and more specifically CWE-121, Buffer Overflow, as the malformed packet data can cause the system to process invalid memory locations or trigger unexpected behavior in the daemon's memory management routines.
The operational impact of CVE-2015-0661 extends beyond simple service disruption to potentially compromise network monitoring capabilities and overall system reliability. Network administrators who rely on SNMP for device monitoring, performance tracking, and configuration management would experience complete loss of SNMP-based visibility during the daemon reload events. The vulnerability is particularly concerning because it requires only authenticated access to exploit, meaning that an attacker with valid SNMP credentials could trigger the denial of service condition without requiring additional privileges or complex attack vectors. This characteristic makes the vulnerability especially dangerous in environments where SNMP access is granted to multiple administrators or automated monitoring systems. The periodic nature of the daemon reloads could also lead to intermittent service degradation, making it difficult for network teams to identify and isolate the root cause of monitoring failures. From an operational security perspective, this vulnerability directly impacts the availability aspect of the CIA triad and could potentially be leveraged as a stepping stone for more sophisticated attacks.
Organizations affected by this vulnerability should implement immediate mitigations to protect their network infrastructure from potential exploitation. The primary recommended approach involves applying the official Cisco security patches and updates that address the input validation issues within the SNMPv2 implementation. Network administrators should also consider implementing SNMP access controls that limit the number of authenticated users with administrative privileges and establish monitoring protocols to detect unusual SNMP traffic patterns that might indicate exploitation attempts. Additional protective measures include configuring SNMPv3 instead of SNMPv2 where possible, as the newer version provides enhanced authentication and encryption capabilities that can help prevent unauthorized access. Network segmentation strategies should be employed to isolate critical network devices from less secure segments, reducing the attack surface available to potential exploiters. From a threat modeling perspective, this vulnerability aligns with ATT&CK technique T1078.004, Valid Accounts, as it exploits legitimate authentication mechanisms to gain access to the system and cause disruption. Security teams should also consider implementing network intrusion detection systems that can identify and alert on malformed SNMP packet patterns that match the characteristics of this vulnerability. The implementation of these mitigations should be prioritized based on the criticality of the affected network devices and the potential impact of service disruption on business operations.