CVE-2013-6693 in IOS
Summary
by MITRE
The MLDP implementation in Cisco IOS 15.3(3)S and earlier on 7600 routers, when many VRFs are configured, allows remote attackers to cause a denial of service (chunk corruption and device reload) by establishing many multicast flows, aka Bug ID CSCue22345.
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Analysis
by VulDB Data Team • 05/15/2017
The vulnerability described in CVE-2013-6693 represents a critical denial of service flaw within Cisco IOS software versions 15.3(3)S and earlier, specifically affecting 7600 series routers. This issue manifests through the Multicast Listener Discovery Protocol (MLDP) implementation, which is responsible for managing multicast group membership on network devices. When routers are configured with multiple Virtual Routing and Forwarding instances, the system becomes particularly susceptible to this vulnerability due to the increased complexity of multicast flow management across different VRF contexts.
The technical flaw stems from improper handling of multicast flow information within the MLDP implementation when numerous VRFs are present. Attackers can exploit this weakness by establishing a large number of multicast flows, which triggers memory corruption within the router's chunk allocation system. This corruption occurs at the kernel level where memory management structures become compromised, leading to unpredictable behavior and ultimately forcing the device to reload automatically. The vulnerability specifically targets the memory management subsystem where chunks of memory are allocated and deallocated during multicast flow processing, creating a condition where legitimate memory operations become corrupted.
The operational impact of this vulnerability is severe and can result in complete network disruption for affected organizations. When triggered, the device reload causes immediate loss of multicast services, potentially affecting critical applications that depend on multicast communication such as video streaming, voice over IP, and real-time data distribution systems. Network administrators may experience extended downtime as the device restarts and re-establishes multicast group memberships, with potential cascading effects on other network services that rely on stable routing and forwarding operations. The vulnerability is particularly dangerous in enterprise environments where 7600 routers serve as core infrastructure components.
Mitigation strategies for this vulnerability include applying the latest Cisco IOS software patches that address the MLDP implementation flaws in affected versions. Organizations should prioritize upgrading their 7600 routers to IOS versions that contain the security fixes for CSCue22345. Network administrators should also consider implementing access control measures to limit the number of multicast flows that can be established, potentially through firewall rules or QoS policies that restrict multicast traffic. Additionally, monitoring systems should be configured to detect unusual multicast flow patterns that may indicate exploitation attempts. From a compliance perspective, this vulnerability aligns with CWE-129, which addresses improper handling of buffer bounds, and represents a significant concern under ATT&CK technique T1499.002, focusing on network denial of service attacks. Organizations should also implement network segmentation strategies to limit the scope of potential exploitation and maintain detailed logging of multicast activities for forensic analysis.