CVE-2012-3918 in IOS
Summary
by MITRE
Cisco IOS before 15.3(1)T on Cisco 2900 devices, when a VWIC2-2MFT-T1/E1 card is configured for TDM/HDLC mode, allows remote attackers to cause a denial of service (serial-interface outage) via certain Frame Relay traffic, aka Bug ID CSCub13317.
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Analysis
by VulDB Data Team • 05/11/2026
Cisco IOS versions prior to 15.3(1)T on Cisco 2900 series devices contain a critical vulnerability in the handling of Frame Relay traffic when configured with VWIC2-2MFT-T1/E1 cards operating in TDM/HDLC mode. This flaw enables remote attackers to trigger a denial of service condition that results in serial interface outages, effectively disrupting network connectivity and service availability. The vulnerability specifically manifests when the device processes certain types of Frame Relay frames that are improperly handled within the TDM/HDLC interface processing pipeline.
The technical root cause of this vulnerability lies in the insufficient input validation and error handling mechanisms within the IOS kernel when processing Frame Relay protocol packets on TDM/HDLC configured interfaces. When maliciously crafted Frame Relay traffic is transmitted to the affected devices, the system fails to properly validate the frame structure and protocol headers, leading to memory corruption or state machine inconsistencies that ultimately cause the serial interface to shut down. This represents a classic buffer overflow condition or improper state management issue that falls under CWE-129, which covers improper validation of length fields, and CWE-248, which addresses unhandled exceptions in the software.
The operational impact of this vulnerability extends beyond simple service disruption as it can affect mission-critical network infrastructure components that rely on TDM/HDLC interfaces for voice and data transmission. Network administrators may experience unexpected outages in voice services, data connectivity, and remote access capabilities that depend on these specific interface configurations. The remote exploitability means that attackers can trigger this condition without physical access or local network credentials, making it particularly dangerous for enterprise and service provider networks where such devices are commonly deployed. This vulnerability aligns with ATT&CK technique T1499.004, which covers network denial of service attacks, and represents a significant threat to network availability and business continuity.
Organizations should prioritize immediate remediation by upgrading affected Cisco 2900 series devices to IOS version 15.3(1)T or later, which contains the necessary patches to address the Frame Relay handling logic. Network administrators should also implement temporary mitigation strategies such as disabling TDM/HDLC mode interfaces when not actively required, implementing traffic filtering rules to block suspicious Frame Relay frames, and monitoring interface status for unusual outages. The vulnerability demonstrates the importance of proper protocol implementation and input validation in network operating systems, highlighting the need for comprehensive security testing of network infrastructure software. Additionally, organizations should consider implementing network segmentation and monitoring solutions to detect and respond to similar anomalies in their network infrastructure.