CVE-2013-6686 in IOS
Summary
by MITRE
The SSL VPN implementation in Cisco IOS 15.3(1)T2 and earlier allows remote authenticated users to cause a denial of service (interface queue wedge) via crafted DTLS packets in an SSL session, aka Bug IDs CSCuh97409 and CSCud90568.
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Analysis
by VulDB Data Team • 12/23/2024
The vulnerability identified as CVE-2013-6686 represents a critical denial of service weakness within Cisco IOS software versions 15.3(1)T2 and earlier, specifically affecting the SSL VPN implementation. This flaw manifests through the improper handling of crafted DTLS packets during SSL sessions, creating a condition where authenticated remote attackers can trigger interface queue wedges that effectively disable network connectivity. The vulnerability impacts Cisco's SSL VPN functionality, which is commonly deployed in enterprise environments for secure remote access, making it particularly concerning for organizations relying on these services for business continuity.
The technical root cause of this vulnerability stems from insufficient input validation and error handling within the DTLS packet processing mechanism of the SSL VPN module. When legitimate SSL sessions are established, the system processes DTLS packets that contain control information and session management data. However, the implementation fails to properly validate the structure and content of these packets, allowing attackers who have authenticated credentials to craft malicious DTLS packets that exploit memory management and queue processing functions. This weakness falls under the category of improper input validation as defined by CWE-20, which specifically addresses issues where applications fail to properly validate input data leading to system instability and potential denial of service conditions.
The operational impact of CVE-2013-6686 extends beyond simple service disruption, creating cascading effects that can compromise entire network segments. When an interface queue wedge occurs, the affected network interface becomes unresponsive and unable to process additional packets, effectively creating a denial of service condition that can persist until the device is manually rebooted or the problematic session is manually cleared. This vulnerability is particularly dangerous because it requires only authenticated access, meaning that attackers with valid user credentials can exploit it without requiring privileged access or sophisticated attack vectors. The attack can be executed from within the network perimeter, making it difficult to detect and prevent through traditional perimeter security measures.
Organizations affected by this vulnerability should prioritize immediate remediation through official Cisco security patches and updates, as the company released specific fixes for this issue in subsequent IOS releases. Network administrators should implement monitoring solutions to detect unusual DTLS packet patterns and establish automated alerting for potential exploitation attempts. The mitigation strategy should include regular security assessments of SSL VPN implementations and enforcement of least privilege access controls to limit the potential impact of authenticated attackers. From an ATT&CK framework perspective, this vulnerability maps to the T1499.004 technique related to network denial of service, and the T1566.001 technique for credential harvesting, as it exploits valid authentication to cause system instability. Additionally, implementing network segmentation and access controls can help limit the scope of potential exploitation while maintaining necessary network functionality for legitimate users.