CVE-2015-4199 in IOS
Summary
by MITRE
Race condition in the IPv6-to-IPv4 functionality in Cisco IOS 15.3S in the Performance Routing Engine (PRE) module on UBR devices allows remote attackers to cause a denial of service (NULL pointer free and module crash) by triggering intermittent connectivity with many IPv6 CPE devices, aka Bug ID CSCug47366.
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Analysis
by VulDB Data Team • 05/21/2022
The vulnerability described in CVE-2015-4199 represents a critical race condition within Cisco IOS 15.3S operating on Universal Bandwidth Router (UBR) devices, specifically affecting the Performance Routing Engine (PRE) module. This flaw manifests in the IPv6-to-IPv4 translation functionality, which serves as a crucial bridge for network connectivity between different addressing protocols. The vulnerability is particularly concerning because it operates at the core networking layer where routing decisions are made, potentially compromising the stability of entire network infrastructures. The issue was identified as Bug ID CSCug47366 and affects devices that must handle significant IPv6 client device connections, making it a prime target for exploitation in environments with substantial IPv6 connectivity demands.
The technical implementation of this race condition occurs within the PRE module's handling of IPv6-to-IPv4 translation processes, where concurrent access to shared memory resources creates a scenario where a NULL pointer is freed while still being referenced. This memory management flaw results from improper synchronization mechanisms during the processing of IPv6 connectivity requests from multiple Customer Premises Equipment (CPE) devices. The vulnerability is triggered when numerous IPv6 CPE devices establish intermittent connections with the affected router, creating a high-frequency scenario that exposes the race condition. The flaw essentially allows attackers to manipulate the timing of memory operations in such a way that the system attempts to free memory that has already been deallocated or is in an inconsistent state, leading to unpredictable behavior and system instability.
The operational impact of this vulnerability extends beyond simple denial of service, as it can lead to complete module crashes and subsequent network disruption across affected UBR devices. Network administrators face the challenge of maintaining stable connectivity when multiple IPv6 CPE devices are present on the network, particularly in environments where IPv6 transition mechanisms are actively deployed. The intermittent nature of the triggering conditions makes this vulnerability particularly difficult to detect and mitigate, as it may not manifest consistently under normal network loads. This characteristic aligns with common patterns observed in race condition vulnerabilities classified under CWE-362, which deals with concurrent execution issues where the timing of operations creates security flaws. The vulnerability's potential for causing sustained network disruption makes it particularly dangerous in mission-critical infrastructure environments where continuous availability is essential.
Mitigation strategies for CVE-2015-4199 should prioritize immediate patch deployment through official Cisco security advisories and firmware updates that address the specific race condition in the PRE module's IPv6-to-IPv4 translation functionality. Network administrators must implement monitoring solutions that can detect unusual patterns of IPv6 CPE device connectivity that might indicate exploitation attempts, utilizing techniques aligned with ATT&CK framework's T1499 sub-technique for network disruption. The implementation of rate limiting and connection throttling mechanisms can help reduce the likelihood of triggering the race condition by limiting the number of concurrent IPv6 connections that can be processed. Additionally, network segmentation strategies should be employed to isolate vulnerable PRE modules from critical network paths, while maintaining regular vulnerability assessments to identify similar race condition vulnerabilities in other network components. The vulnerability's classification under CWE-362 emphasizes the need for proper synchronization mechanisms and memory management practices in network device software development, reinforcing industry standards that require robust handling of concurrent operations in network infrastructure software.