CVE-2015-6432 in IOS XR
Summary
by MITRE
Cisco IOS XR 4.2.0, 4.3.0, 5.0.0, 5.1.0, 5.2.0, 5.2.2, 5.2.4, 5.3.0, and 5.3.2 does not properly restrict the number of Path Computation Elements (PCEs) for OSPF LSA opaque area updates, which allows remote attackers to cause a denial of service (device reload) via a crafted update, aka Bug ID CSCuw83486.
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Analysis
by VulDB Data Team • 07/02/2022
The vulnerability described in CVE-2015-6432 represents a critical denial of service flaw affecting Cisco IOS XR software versions spanning multiple release branches including 4.2.0 through 5.3.2. This issue specifically targets the Path Computation Element (PCE) functionality within the OSPF LSA opaque area update processing mechanism, where the software fails to properly enforce limits on the number of PCEs that can be included in a single update message. The flaw exists at the protocol implementation level where the system lacks adequate input validation and resource management controls for handling PCE data within OSPF link state advertisements. The vulnerability is particularly concerning as it allows remote attackers to exploit this weakness without requiring authentication, making it accessible to any network entity capable of communicating with the affected device. The impact of exploitation manifests as a complete device reload or system crash, effectively rendering the network device unavailable and disrupting critical network services.
The technical root cause of this vulnerability lies in the insufficient bounds checking and resource allocation mechanisms within the OSPF implementation of Cisco IOS XR. When processing OSPF LSA opaque area updates containing Path Computation Elements, the system does not properly validate or constrain the number of PCE entries that can be processed in a single update message. This lack of proper input validation creates a condition where an attacker can craft a malicious update containing an excessive number of PCE entries, causing the device to consume excessive memory resources or trigger internal processing errors. The flaw operates at the network protocol processing layer where the device attempts to parse and store PCE information in its routing tables and memory structures, leading to resource exhaustion or memory corruption. According to CWE classification, this vulnerability maps to CWE-129 Input Validation and Bounds Checking, while the ATT&CK framework would categorize this under TA0040 Initial Access with T1190 Exploit Public-Facing Application as the attack vector involves exploiting a protocol implementation weakness.
The operational impact of CVE-2015-6432 extends beyond simple service disruption to potentially compromise network reliability and availability in production environments. Network administrators managing devices running affected IOS XR versions face significant operational challenges as this vulnerability can be exploited remotely without any authentication requirements, making it particularly dangerous in untrusted network segments. The device reload condition caused by this flaw can result in cascading failures throughout the network infrastructure, especially in environments where multiple devices are interconnected through OSPF routing protocols. Organizations with extensive deployments of Cisco IOS XR devices may experience widespread service degradation or complete network outages if attackers successfully exploit this vulnerability. The vulnerability affects critical infrastructure components that rely on OSPF for dynamic routing, making it particularly impactful for service providers and enterprise networks where network availability is paramount for business continuity. The exploitability of this vulnerability means that network devices in the affected versions are inherently at risk, requiring immediate attention and remediation to prevent potential service disruption.
Mitigation strategies for CVE-2015-6432 should prioritize immediate software updates to the latest available IOS XR releases that contain the necessary patches for this vulnerability. Cisco has released security advisories and software updates addressing this specific issue, and organizations should implement these patches as part of their vulnerability management processes. Network administrators should also consider implementing access controls and firewall rules to limit OSPF traffic to trusted sources, reducing the attack surface for this particular vulnerability. Additionally, monitoring and logging of OSPF LSA updates can help detect anomalous patterns that may indicate exploitation attempts. The implementation of rate limiting mechanisms for OSPF updates and the configuration of appropriate resource limits for PCE processing can provide additional defense in depth. Organizations should also conduct thorough network segmentation to ensure that potentially compromised segments cannot affect critical network infrastructure. Regular vulnerability assessments and penetration testing should be performed to identify other potential weaknesses in the network architecture that could be exploited in conjunction with this vulnerability. The remediation process should include comprehensive testing of patched systems to ensure that the vulnerability is fully resolved without introducing new operational issues.