CVE-2012-3893 in IOS
Summary
by MITRE
The FlexVPN implementation in Cisco IOS 15.2 and 15.3 allows remote authenticated users to cause a denial of service (spoke crash) via spoke-to-spoke traffic, aka Bug ID CSCtz02622.
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Analysis
by VulDB Data Team • 04/17/2017
The vulnerability described in CVE-2012-3893 represents a significant denial of service flaw within Cisco's IOS software implementation of FlexVPN functionality. This issue specifically affects versions 15.2 and 15.3 of the Cisco IOS operating system, where the FlexVPN implementation contains a critical design flaw that can be exploited by authenticated remote attackers to crash spoke devices within the VPN infrastructure. The vulnerability manifests when spoke-to-spoke traffic traverses the network, creating a condition that leads to system instability and complete service disruption.
The technical root cause of this vulnerability stems from improper handling of certain packet processing sequences within the FlexVPN module of Cisco IOS. When authenticated users send specific types of traffic between spoke devices in a FlexVPN configuration, the system fails to properly validate or process these packets, leading to memory corruption or resource exhaustion that ultimately results in the device crashing. This flaw operates at the network protocol level where the system's packet handling logic does not adequately account for certain edge cases in spoke-to-spoke communication patterns. The vulnerability falls under CWE-121, which describes buffer overflow conditions, and more specifically relates to improper handling of network traffic in VPN implementations.
The operational impact of this vulnerability is severe for organizations relying on Cisco FlexVPN deployments, as it can result in complete disruption of VPN services across affected network segments. When a spoke device crashes, all connections originating from or terminating at that device become unavailable, potentially affecting hundreds or thousands of users depending on the network topology. The authentication requirement for exploitation adds a layer of complexity to the threat model, as attackers must first establish valid credentials to access the network before they can execute the attack. This characteristic makes the vulnerability particularly dangerous in environments where credential compromise is possible, as it can be exploited to create sustained denial of service conditions that are difficult to detect and mitigate.
Organizations affected by this vulnerability should implement immediate mitigations including applying the relevant Cisco security patches and updates released to address the specific flaw. Network administrators should also consider implementing traffic filtering rules that can detect and block the specific packet patterns that trigger the vulnerability. The mitigation strategies align with ATT&CK technique T1499.004, which covers network disruption attacks, and organizations should implement monitoring solutions to detect unusual traffic patterns that may indicate exploitation attempts. Additionally, network segmentation and redundant spoke device configurations can help reduce the impact of such attacks by ensuring that a single device crash does not bring down entire network segments. Regular security assessments and vulnerability scanning should be conducted to identify other potential weaknesses in the VPN infrastructure that could be exploited in conjunction with this vulnerability.