CVE-2026-20270 is a high-severity vulnerability in Cisco IOS XE Software with a CVSS score of 8.6. It involves incorrect calculation, including integer overflow, underflow, and truncation. Cisco has released fixes in versions 17.9.10, 17.12.8, 17.15.6, 17.18.4/17.18.4a, and 26.1.2.