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-2020-3569HighActively exploited
Multiple vulnerabilities in the Distance Vector Multicast Routing Protocol (DVMRP) feature of Cisco IOS XR Software could allow an unauthenticated, remote attacker to immediately crash the IGMP process or cause memory exhaustion and eventual crash. This is due to incorrect handling of IGMP packets.
- CVE-2020-3566HighActively exploited
A vulnerability in the Distance Vector Multicast Routing Protocol (DVMRP) feature of Cisco IOS XR Software could allow an unauthenticated, remote attacker to exhaust process memory of an affected device. This is due to insufficient queue management for IGMP packets.
- CVE-2026-20280High
A vulnerability in Cisco IOS XR Software was discovered during an internal security review. It relates to improper checking or handling of exceptional conditions, classified as CWE-703.
- CVE-2026-20278High
A vulnerability in Cisco IOS XR Software was discovered during an internal security review. It relates to improper neutralization issues, classified as CWE-707.
- CVE-2026-20277High
A vulnerability in Cisco IOS XR Software was discovered during an internal security review. It relates to protection mechanism failure issues, classified as CWE-693.
- CVE-2026-20276High
A vulnerability in Cisco IOS XR Software was discovered during an internal security review. It relates to insufficient control flow management issues, classified as CWE-691.
- CVE-2026-20275High
A vulnerability in Cisco IOS XR Software was discovered during an internal security review. It relates to incorrect calculation issues, classified as CWE-682.
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.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS