Cisco IOS XE Software vulnerability

What happened

As part of Cisco's ongoing commitment to proactive security and product quality, the Cisco IOS XE Software engineering team has conducted a comprehensive internal security review. This review resulted in software hardening releases that address multiple internally discovered vulnerabilities. The vulnerabilities tracked by CVE-2026-20270 are related to incorrect calculation issues that are grouped under the Common Weakness Enumeration (CWE) Pillar CWE-682.

Affected versions

Cisco IOS XE Software: 17.2.1a; 16.12.1y; 16.12.3s; 16.7.1b; 16.6.2; 16.6.5; 16.12.1w; 16.9.1d; 17.3.1; 16.9.4c; 16.7.1; 17.2.1; 16.6.8; 16.9.1b; 16.9.2s; 16.12.4; 16.12.3a; 17.1.1s; 16.11.1a; 16.7.2; 16.11.1b; 16.9.1s; 16.9.3h; 16.9.1c; 16.6.5a; 16.6.3; 16.10.1f; 17.2.1v; 16.8.1e; 16.9.3a; 16.12.1a; 16.12.1x; 16.6.4s; 16.10.1c; 16.12.3; 16.11.2; 16.6.5b; 16.12.2s; 16.10.1b; 16.7.3; 16.6.7; 16.9.6; 16.9.2; 16.10.1; 16.12.1t; 16.9.1; 16.8.1a; 16.9.3s; 16.6.7a; 16.12.2; 16.11.1; 16.9.3; 16.11.1s; 16.12.1; 17.1.1; 17.1.2; 16.10.1d; 17.1.1t; 16.9.4; 16.8.3; 16.12.2t; 16.9.5; 16.8.1s; 16.10.1e; 16.8.2; 16.6.4; 16.8.1b; 16.10.1a; 16.12.1z; 16.8.1c; 16.9.1a; 16.6.4a; 16.10.1g; 16.8.1; 16.6.6; 16.9.2a; 16.8.1d; 16.10.3; 16.7.1a; 16.11.1c; 16.10.1s; 17.2.1r; 17.1.1a; 16.10.2; 16.12.2a; 16.12.1c; 16.12.1s; 16.7.4; 17.2.2; 16.9.8; 16.9.7; 17.1.3; 17.3.1a; 17.3.2a; 16.12.5; 17.3.1w; 17.3.2; 17.4.1; 16.12.4a; 17.4.1a; 17.3.1x; 17.3.3; 16.6.9; 17.2.3; 17.5.1; 16.12.1z1; 16.12.5a; 17.4.1b; 17.3.1z; 16.12.5b; 17.4.2; 17.3.3a; 17.3.5; 17.3.4; 17.5.1a; 16.12.6; 17.6.1; 16.12.1z2; 16.6.10; 17.3.4a; 17.6.1a; 17.7.1; 17.6.1x; 17.6.2; 16.12.6a; 17.3.4c; 17.4.2a; 17.3.4b; 17.7.1a; 16.12.7; 17.8.1a; 17.6.3a; 17.6.3; 17.7.2; 17.7.1b; 17.9.1w; 17.3.5a; 17.6.1z; 16.12.8; 17.8.1; 17.9.1; 17.6.4; 17.3.5b; 17.9.1a; 17.3.6; 17.10.1; 16.9.8a; 17.6.1z1; 17.10.1a; 17.9.2; 17.6.5; 17.9.1x; 17.9.1y; 16.9.8b; 17.3.7; 17.9.2a; 17.9.3; 16.12.9; 17.11.1; 17.10.1b; 17.6.6; 17.9.1x1; 17.11.1a; 17.9.3a; 17.12.1; 17.3.8; 17.9.4; 16.12.10; 17.12.1w; 17.9.1y1; 17.12.1a; 17.9.5; 17.13.1; 17.12.1x; 17.12.2; 17.14.1; 17.9.4a; 17.3.8a; 17.6.6a; 17.6.5a; 17.6.7; 16.12.10a; 17.15.1; 17.13.1a; 17.12.2a; 16.12.11; 17.12.3; 17.12.1y; 17.12.1z; 17.9.5a; 17.14.1a; 17.9.5b; 17.6.8; 16.12.12; 17.12.4; 17.9.6; 17.17.1; 17.16.1; 17.15.1w; 17.12.3a; 17.9.5c; 17.15.1a; 17.12.1z1; 17.15.2; 17.15.1b; 17.9.5d; 17.15.1x; 17.9.6a; 17.12.1z2; 17.6.8a; 17.16.1a; 16.12.13; 17.15.3; 17.9.7; 17.12.5; 17.15.1y; 17.9.5e; 17.12.4a; 17.15.2a; 17.15.2c; 17.15.2b; 17.12.1z3; 17.9.5f; 17.12.4b; 17.12.5a; 17.18.1; 17.12.6; 17.12.1z4; 17.9.8; 17.9.7a; 17.15.3a; 17.15.4; 17.12.5b; 17.15.3b; 16.12.14; 17.18.1z; 17.9.7b; 17.12.5c; 26.1.1; 17.18.1a; 17.15.4a; 17.18.2; 17.18.1w; 17.15.4b; 17.12.6a; 17.12.7; 17.15.4c; 17.9.9; 17.12.5d; 16.12.15; 17.15.4s1; 17.15.5; 17.12.1z5; 17.18.1x; 17.12.1z6; 17.15.4d; 17.12.6b; 17.4.1c; 17.15.5a; 17.18.1y; 17.12.7a; 17.18.3; 17.12.7b; 17.18.3a; 26.1.1a; 17.15.7; 16.12.16; 17.18.5x; 26.1.3; 17.12.9; 17.18.5 Fixed: See vendor advisory.

Why it matters

Review the vendor advisory and exposure of the affected product to determine operational impact.

Detection & mitigation

• Apply vendor-provided updates or mitigations.
• Review affected product exposure and access logs.