Vulnerability in Cisco iOS Xr Software
CVE-2026-20074
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.
Published · last modified .
CVSS v3 metric
CVSS v3 base score 7.4 (High). Vector: CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H.
EPSS exploit prediction
EPSS: 0.002 (4.4th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 4th percentile — 4.4% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.002 · newest: 0.002 · change: 0.000
Affected products
- Cisco iOS Xr Software — versions 7.8.1, 7.9.1, 7.10.1
- Cisco iOS Xr — versions 25.3.0
Weakness classification (CWE)
References
- sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-… (Mitigation, Vendor Advisory)
Frequently asked questions
- What is CVE-2026-20074?
- CVE-2026-20074 is a high-severity vulnerability in Cisco iOS Xr Software, classified under CWE-1287. CVSS score: 7.4/10. Published 2026-03-11.
- How severe is CVE-2026-20074?
- High severity. CVSS v3 base score is 7.4 out of 10.