What is the CVSS score of CVE-2026-20271?

CVE-2026-20271 has a CVSS 3.1 base score of 8.6 (High). CVSS vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H. EPSS exploitation probability: 0.3%.

Which versions of Cisco IOS XE are affected by CVE-2026-20271?

Cisco IOS XE Software versions 16.6.x through 26.1.x contain an unauthenticated remote denial-of-service vulnerability (CVE-2026-20271, CVSS 8.6) capable of forcing device reloads, affecting…

How to fix or mitigate CVE-2026-20271?

Within 24 hours, conduct a complete asset inventory of all Cisco IOS XE devices and document installed versions, prioritizing production and critical infrastructure segments. Within 7 days, implement network access controls restricting unauthenticated connections to management interfaces on affected devices, coordinate with Cisco technical support to establish patch timeline expectations, and deploy monitoring to detect abnormal device reloads or unexpected availability degradation. Within 30 days, maintain active tracking of Cisco security advisories for patch releases, validate patches in a staging environment immediately upon release, and execute a prioritized deployment plan rolling patched versions to critical devices first.

Cisco IOS XE CVE-2026-20271

EUVD-2026-53457 HIGH

Insufficient Control Flow Management (CWE-691)

2026-08-05 cisco

GHSA-g2mx-jm98-x82v

Information Disclosure Apple Cisco Cisco Ios Xe Software

8.6

CVSS 3.1 · Vendor: cisco

Severity by source

Vendor (cisco) PRIMARY

8.6 HIGH

AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H

vuln.today AI

8.6 HIGH

IOS XE processes unauthenticated network traffic; scope change reflects full device reload impacting all services; no confidentiality or integrity impact is supported by the description.

3.1 AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H

4.0 AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:H

Primary rating from Vendor (cisco).

CVSS VectorVendor: cisco

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

None

Scope

Changed

Confidentiality

None

Integrity

None

Availability

High

Lifecycle Timeline

Analysis Generated

Aug 05, 2026 - 17:27 vuln.today

CVE Published

Aug 05, 2026 - 16:19 nvd

HIGH 8.6

DescriptionCVE.org

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.  

AnalysisAI

Unauthenticated remote denial-of-service in Cisco IOS XE Software allows network-accessible attackers to crash IOS processes or force full device reloads by exploiting insufficient control flow management flaws (CWE-691), with a scope-changing availability impact rated CVSS 8.6. The vulnerabilities were discovered internally by Cisco's own engineering team as part of a proactive security review and addressed through software hardening releases - no active exploitation or public proof-of-concept has been identified at time of analysis. The affected version range is exceptionally broad, spanning IOS XE 16.6.x through 26.1.x, meaning virtually every Cisco IOS XE device on networks that has not been recently patched is likely running a vulnerable version.

Technical ContextAI

Cisco IOS XE is the Linux-kernel-based network operating system running on Cisco's enterprise routing and switching platforms, including Catalyst, ASR, ISR, CSR, and related families. The CPE string cpe:2.3:a:cisco:cisco_ios_xe_software:*:*:*:*:*:*:*:* confirms the vulnerability applies across all IOS XE platform sub-variants without exception. CWE-691 (Insufficient Control Flow Management) is a pillar-level weakness that encompasses improper exception handling, state machine logic errors, unreachable code, and malformed loop termination - root causes that in packet-processing or protocol-handling code paths can trigger IOS process crashes or full device reloads. Cisco's grouping of multiple distinct findings under a single CVE is consistent with their practice of consolidating related internally discovered defects into one advisory. The CVSS S:C scope-change metric indicates the availability impact extends beyond the initially faulting process, consistent with a device reload disrupting all routing, switching, and management services on the affected platform.

RemediationAI

The primary remediation is upgrading to a Cisco-released fixed version of IOS XE Software as specified in the Software Fixed Releases table within the Cisco Security Advisory at https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-hardening-iosxe-V8NMuMZJ - specific fixed version numbers are not present in the available intelligence data and must be confirmed directly from that advisory before planning upgrades. For organizations unable to immediately upgrade, the following compensating controls reduce exposure: deploy Control Plane Policing (CoPP) policies to rate-limit and filter unexpected or malformed traffic destined to the IOS XE control plane, reducing the attack surface for protocol-level triggering; apply Infrastructure Access-Lists (iACLs) to restrict which source addresses can reach management-plane and control-plane interfaces; and ensure management access (SSH, SNMP, NETCONF) is restricted to dedicated out-of-band management networks. These controls reduce but do not eliminate risk, particularly if the vulnerability is triggered by transit data-plane traffic rather than management-plane sessions - the exact trigger surface is not publicly documented, limiting the precision of protocol-specific workarounds.