CVE-2019-1910 in IOS XR
Summary
by MITRE
A vulnerability in the implementation of the Intermediate System–to–Intermediate System (IS–IS) routing protocol functionality in Cisco IOS XR Software could allow an unauthenticated attacker who is in the same IS–IS area to cause a denial of service (DoS) condition. The vulnerability is due to incorrect processing of crafted IS–IS link-state protocol data units (PDUs). An attacker could exploit this vulnerability by sending a crafted link-state PDU to an affected system to be processed. A successful exploit could allow the attacker to cause all routers within the IS–IS area to unexpectedly restart the IS–IS process, resulting in a DoS condition. This vulnerability affects Cisco devices if they are running a vulnerable release of Cisco IOS XR Software earlier than Release 6.6.3 and are configured with the IS–IS routing protocol. Cisco has confirmed that this vulnerability affects both Cisco IOS XR 32-bit Software and Cisco IOS XR 64-bit Software.
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Analysis
by VulDB Data Team • 07/22/2020
The vulnerability identified as CVE-2019-1910 represents a critical denial of service weakness within Cisco IOS XR Software that specifically targets the Intermediate System-to-Intermediate System routing protocol implementation. This flaw exists in the processing of link-state protocol data units and affects devices running IOS XR Software versions prior to 6.6.3. The vulnerability operates at the network protocol level where IS-IS routing information is exchanged between network devices, making it particularly dangerous in production environments where network stability is paramount. The issue manifests when an unauthenticated attacker within the same IS-IS area can manipulate protocol data units to trigger unexpected behavior in the routing process.
The technical exploitation of this vulnerability occurs through the deliberate crafting of IS-IS link-state PDUs that contain malformed or specially constructed data elements. These crafted PDUs are processed by the vulnerable IOS XR software implementation, which fails to properly validate or handle the malformed data structures. The specific flaw lies in the insufficient input validation mechanisms within the IS-IS protocol stack, causing the system to crash or restart the IS-IS process when encountering these malformed packets. This behavior follows the CWE-129 weakness classification related to improper validation of input boundaries and aligns with ATT&CK technique T1499.002 for network denial of service attacks.
The operational impact of this vulnerability extends beyond simple service disruption as it can cause cascading failures throughout the entire IS-IS area. When a single router experiences the DoS condition, the restart of the IS-IS process forces all routers within that same area to reinitialize their routing tables and redistribute routing information. This creates a network-wide disruption that can last from several minutes to hours depending on the size and complexity of the affected network topology. Network administrators may experience significant downtime as routing convergence processes take time to restore normal operations, potentially affecting critical network services and applications that depend on stable routing information.
Organizations affected by this vulnerability should immediately implement mitigation strategies focusing on network segmentation and access control measures. The primary recommended action is to upgrade affected Cisco IOS XR devices to version 6.6.3 or later, which contains the necessary patches to address the input validation weaknesses. Network administrators should also consider implementing access control lists or firewall rules to restrict IS-IS traffic to trusted sources within the same area, preventing unauthorized access to the routing protocol. Additionally, monitoring systems should be enhanced to detect unusual restart patterns in IS-IS processes, which could indicate exploitation attempts. The vulnerability demonstrates the importance of maintaining up-to-date network firmware and implementing proper network segmentation strategies as outlined in the NIST Cybersecurity Framework and ISO 27001 security standards.