CVE-2026-20074
HighCVSS 7.4Exploitation Probability (EPSS)
Low risk6th percentile - higher than 6% of all known CVEs
Summary
A vulnerability in the IS-IS multi-instance routing feature of Cisco IOS XR Software allows an unauthenticated, adjacent attacker to cause an unexpected restart of the IS-IS process. The issue is due to insufficient input validation of incoming IS-IS packets.
Risk Assessment
Successful exploitation leads to temporary loss of connectivity to advertised networks, causing a denial of service (DoS) condition for network traffic.
Recommendation
Apply the patches provided by Cisco in the security advisory immediately and restrict trusted IS-IS adjacencies to the necessary minimum.
Other vulnerabilities in Cisco IOS XR Software
See all- CVE-2017-6731High
A vulnerability in Multicast Source Discovery Protocol (MSDP) ingress packet processing for Cisco IOS XR Software could allow an unauthenticated, remote attacker to cause the MSDP session to be unexpectedly reset, leading to a short denial of service (DoS) condition. The MSDP session will restart within a few seconds.
- CVE-2017-6728High
A vulnerability in the CLI of Cisco IOS XR Software could allow an authenticated, local attacker to execute arbitrary code at the root privilege level on an affected system, due to Incorrect Permissions.
- CVE-2016-9205High
A vulnerability in the HTTP 2.0 request handling code of Cisco IOS XR Software could allow an unauthenticated, remote attacker to cause the Event Management Service daemon (emsd) to crash, resulting in a denial of service (DoS) condition.
- CVE-2026-20046High
A vulnerability in Cisco IOS XR Software allows a local attacker with low privileges to elevate privileges to full administrative control over the device. The issue stems from incorrect mapping of a CLI command to task groups in the source code.
- CVE-2026-20040High
A vulnerability in the CLI of Cisco IOS XR Software allows an authenticated local attacker to execute arbitrary commands as root on the underlying operating system. This is due to insufficient validation of user arguments passed to specific CLI commands.
Original NVD description (English source)
A vulnerability in the Intermediate System-to-Intermediate System (IS-IS) multi-instance routing feature of Cisco IOS XR Software could allow an unauthenticated, adjacent attacker to cause the IS-IS process to restart unexpectedly. This vulnerability is due to insufficient input validation of ingress IS-IS packets. An attacker could exploit this vulnerability by sending crafted IS-IS packets to an affected device after forming an adjacency. A successful exploit could allow the attacker to cause the IS-IS process to restart unexpectedly, resulting in a temporary loss of connectivity to advertised networks and a denial of service (DoS) condition. Note: The IS-IS protocol is a routing protocol. To exploit this vulnerability, an attacker must be Layer 2-adjacent to the affected device and must have formed an adjacency.