Vulnerability intelligence
CVE-2026-20271 and is rated High severity with a CVSS score of 8.6. It is not in the current CISA KEV record we collected. That does not prove exploitation has not occurred.
To assist customers in patching and streamline the disclosure process, Cisco has grouped these issues by their underlying vulnerability class - Common Weakness Enumeration (CWE) - and assigned a single Common Vulnerabilities and Exposures identifier (CVE ID).
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-2026-20271 are related to insufficient control flow management issues that are grouped under the Common Weakness Enumeration (CWE) Pillar CWE-691.
Source: NVD
Cisco Security Advisories · Updated Oct 2, 2026
These vulnerabilities affect Cisco IOS XE Software when it is running in autonomous or controller mode, regardless of device configuration.
For information about which Cisco software releases are vulnerable, see the Fixed Software section of this advisory.
Note: Cisco IOS XE Software releases 16.12 and earlier for Cisco Catalyst 3650 and 3850 Series Switches are affected by these vulnerabilities. Cisco will not release a security-hardened version of Cisco IOS XE Software Release 16.12. High-risk issues that are confirmed to affect Cisco Catalyst 3650 and 3850 Series Switches will be fixed in a future release as outlined in the public Cisco Security Vulnerability Policy.
Customers with questions or concerns about hardening releases for Cisco IOS XE Software releases 16.12 and earlier should reach out to their Cisco representative or to the Cisco Technical Assistance Center (TAC).
There are no workarounds that address these vulnerabilities.
To fully remediate these vulnerabilities and avoid future exposure as described in this advisory, Cisco strongly recommends that customers upgrade to the fixed software indicated in this advisory.
In the following table, the left column lists Cisco software releases. The right column indicates whether a release is affected by the vulnerabilities that are described in this advisory and the first release that includes the fix for these vulnerabilities. Customers are advised to upgrade to an appropriate fixed software release as indicated in this section.
Cisco IOS XE Software Release | First Fixed Release |
|---|---|
17.8 and earlier | Migrate to a fixed release. |
17.9 | 17.9.10 |
17.12 | 17.12.8 |
17.15 | 17.15.6 |
17.18 | 17.18.4, 17.18.4a |
26.1 | 26.1.2 |
The Cisco Product Security Incident Response Team (PSIRT) validates only the affected and fixed release information that is documented in this advisory.
The Cisco PSIRT is not aware of any public announcements or malicious use of the vulnerabilities that are described in this advisory.