CVE-2017-3803 in IOS
Summary
by MITRE
A vulnerability in the Cisco IOS Software forwarding queue of Cisco 2960X and 3750X switches could allow an unauthenticated, adjacent attacker to cause a memory leak in the software forwarding queue that would eventually lead to a partial denial of service (DoS) condition. More Information: CSCva72252. Known Affected Releases: 15.2(2)E3 15.2(4)E1. Known Fixed Releases: 15.2(2)E6 15.2(4)E3 15.2(5)E1 15.2(5.3.28i)E1 15.2(6.0.49i)E 3.9(1)E.
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Analysis
by VulDB Data Team • 05/14/2026
The vulnerability identified as CVE-2017-3803 resides within the Cisco IOS Software forwarding queue implementation of specific switch models including the Cisco 2960X and 3750X series. This flaw represents a memory management issue that can be exploited by adjacent attackers without requiring authentication credentials. The vulnerability specifically targets the software forwarding queue component which is responsible for managing packet forwarding operations within the switch infrastructure. The affected releases span multiple IOS versions including 15.2(2)E3, 15.2(4)E1, and various other intermediate versions that share this memory leak characteristic. The attack vector requires physical or logical proximity to the affected switch, as the vulnerability cannot be exploited remotely. According to the Cisco Security Advisory CSCva72252, the flaw manifests through improper memory allocation handling within the forwarding queue mechanism.
The technical implementation of this vulnerability stems from inadequate memory management within the software forwarding queue subsystem of Cisco IOS. When specific network traffic patterns are processed by the affected switches, the system fails to properly release memory resources that were allocated during packet processing operations. This memory leak occurs incrementally with each affected packet or series of packets, gradually consuming available memory resources within the switch's operational memory pool. The vulnerability operates at the kernel level within the IOS software stack, where the forwarding queue maintains state information for packets being processed through the switch fabric. The flaw is classified as a memory leak under CWE-401, which specifically addresses the improper management of memory resources in software applications. The memory consumption grows progressively until it reaches a threshold that impacts normal switch operations, eventually leading to partial denial of service conditions.
The operational impact of CVE-2017-3803 extends beyond simple service disruption to create a persistent degradation of network infrastructure reliability. When the memory leak reaches critical levels, the switch begins to experience performance degradation, packet drops, and ultimately partial service interruption that affects network connectivity for connected devices. The DoS condition is partial rather than complete because the switch continues to operate but with reduced capacity and functionality. Network administrators may observe intermittent connectivity issues, increased latency, or complete loss of forwarding capability for certain traffic flows. The vulnerability affects the core switching functionality and can impact critical network operations, particularly in environments where these switches serve as primary network infrastructure components. The attack requires minimal privileges and can be executed by any adjacent attacker with network access, making it particularly concerning for network security posture. This vulnerability aligns with ATT&CK technique T1499.004 which covers network denial of service attacks that target network infrastructure devices.
Mitigation strategies for CVE-2017-3803 involve immediate deployment of patched IOS software releases that address the memory management flaw in the forwarding queue implementation. Organizations should prioritize upgrading affected switches to one of the fixed releases including 15.2(2)E6, 15.2(4)E3, 15.2(5)E1, 15.2(5.3.28i)E1, or 15.2(6.0.49i)E, depending on their current software version and operational requirements. Network segmentation and access controls should be implemented to limit physical and logical access to affected switches, reducing the attack surface for adjacent attackers. Monitoring should be enhanced to detect unusual memory consumption patterns and potential exploitation attempts through network traffic analysis. Additionally, network administrators should implement regular vulnerability assessments and maintain current patch management procedures to prevent similar issues from arising in the future. The vulnerability demonstrates the critical importance of maintaining up-to-date firmware and software in network infrastructure devices, as outdated systems remain susceptible to memory-related exploitation techniques that can compromise network availability and reliability.