Summary: 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. These vulnerabilities were found during internal testing and are not known to be actively exploited. 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). Cisco has released software updates that address these vulnerabilities. There are no workarounds that address these vulnerabilities.

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Vulnerable Products: 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 ["#fs"] section of this advisory. Note: This evaluation focused on Cisco IOS XE Software releases 17.9, 17.12, 17.15, 17.18, and 26.1. Cisco Catalyst 3650 and 3850 Series Switches do not run any of these releases and therefore were not evaluated as part of this review. Any vulnerabilities that are confirmed to affect Cisco Catalyst 3650 and 3850 Series Switches will be fixed in a future release as outlined in our public Security Vulnerability Policy ["https://sec.cloudapps.cisco.com/security/center/resources/security_vulnerability_policy.html"].

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Products Confirmed Not Vulnerable: Only products listed in the Vulnerable Products ["#vp"] section of this advisory are known to be affected by this vulnerability.

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Details: The following table outlines the vulnerability classes that are addressed in these software hardening releases. The CVSS score that is assigned to each CVE ID represents the maximum potential severity of the single most impactful underlying bug within that specific CWE category. CVE ID Highest CVSS Score Vulnerability Class (Highest-Level CWE) Description CVE-2026-20267 9.0 CWE-284 Improper access control (covers authorization, authentication, privileges, and bypasses) CVE-2026-20268 8.6 CWE-119 Improper restriction of operations within the bounds of a memory buffer (covers buffer overflows and out-of-bounds writes) CVE-2026-20269 8.6 CWE-664 Improper control of a resource through its lifetime (covers memory and file handlers, null pointer dereferences, invalid frees) CVE-2026-20270 8.6 CWE-682 Incorrect calculation (covers arithmetic or numeric conversion errors including integer overflow, underflow, truncation) CVE-2026-20271 8.6 CWE-691 Insufficient control flow management (covers infinite loops, uncontrolled recursion, race conditions) CVE-2026-20272 9.8 CWE-74 Improper neutralization of special elements (covers command, OS, argument injection) CVE-2026-20273 8.6 CWE-20 Improper input validation (covers input validation, path traversal, and external path control)

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Workarounds: There are no workarounds that address these vulnerabilities.

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Fixed Software: 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. Fixed Releases 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 ["https://sec.cloudapps.cisco.com/security/center/resources/security_vulnerability_policy.html#fixes"] as indicated in this section. Cisco IOS XE Software Release First 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.

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Vulnerability Policy: To learn about Cisco security vulnerability disclosure policies and publications, see the Security Vulnerability Policy ["http://www.cisco.com/web/about/security/psirt/security_vulnerability_policy.html"]. This document also contains instructions for obtaining fixed software and receiving security vulnerability information from Cisco. For additional information on Cisco's vulnerability management, disclosure cadence, and software patching strategy, see Cisco's Transition to a Risk-Based Vulnerability Disclosure Model ["https://sec.cloudapps.cisco.com/security/center/resources/risk-based-disclosure"].

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Exploitation and Public Announcements: The Cisco PSIRT is not aware of any public announcements or malicious use of the vulnerabilities that are described in this advisory.

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Source: These vulnerabilities were found during internal security testing using existing testing processes as well as frontier AI models.

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Legal Disclaimer: SOFTWARE DOWNLOADS AND TECHNICAL SUPPORT The Cisco Support and Downloads ["https://www.cisco.com/c/en/us/support/index.html"] page on Cisco.com provides information about licensing and downloads. This page can also display customer device support coverage for customers who use the My Devices tool. Please note that customers may download only software that was procured from Cisco directly or through a Cisco authorized reseller or partner and for which the license is still valid. Customers who purchase directly from Cisco but do not hold a Cisco service contract and customers who make purchases through third-party vendors but are unsuccessful in obtaining fixed software through their point of sale should obtain upgrades by contacting the Cisco Technical Assistance Center (TAC) ["https://www.cisco.com/c/en/us/support/web/tsd-cisco-worldwide-contacts.html"]. Customers should have the product serial number available and be prepared to provide the URL of this advisory as evidence of entitlement to a free upgrade. When considering software upgrades ["https://sec.cloudapps.cisco.com/security/center/resources/security_vulnerability_policy.html#fixes"], customers are advised to regularly consult the advisories ["https://www.cisco.com/go/psirt"] for the relevant Cisco products to determine exposure and a complete upgrade solution. In all cases, customers should ensure that the devices to be upgraded contain sufficient memory and confirm that current hardware and software configurations will continue to be supported properly by the new release. If the information is not clear, customers are advised to contact the Cisco Technical Assistance Center (TAC) ["https://www.cisco.com/c/en/us/support/web/tsd-cisco-worldwide-contacts.html"] or their contracted maintenance providers. LEGAL DISCLAIMER DETAILS CISCO DOES NOT MAKE ANY EXPRESS OR IMPLIED GUARANTEES OR WARRANTIES OF ANY KIND, INCLUDING THE WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR USE. WITHOUT LIMITING THE GENERALITY OF THE FOREGOING, CISCO DOES NOT GUARANTEE THE ACCURACY OR COMPLETENESS OF THIS INFORMATION. THIS DOCUMENT IS PROVIDED ON AN "AS IS" BASIS. YOUR USE OF THE INFORMATION ON THE DOCUMENT OR MATERIALS LINKED FROM THE DOCUMENT IS AT YOUR OWN RISK. CISCO RESERVES THE RIGHT TO CHANGE OR UPDATE THIS DOCUMENT AT ANY TIME. Copies or summaries of the information contained in this Security Advisory may lack important information or contain factual errors. Customers are advised to visit the Cisco Security Advisories ["https://www.cisco.com/go/psirt"] page for the most recent version of this Security Advisory. The Cisco Product Security Incident Response Team (PSIRT) assesses only the affected and fixed release information that is documented in this advisory. See the Cisco Security Vulnerability Policy ["https://sec.cloudapps.cisco.com/security/center/resources/security_vulnerability_policy.html#fixes"] for more information.