What is the CVSS score of CVE-2026-20270?

CVE-2026-20270 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-2026-20270?

A vulnerability in Cisco IOS XE devices (used in most enterprise routers and switches) allows any network-connected attacker to remotely crash these devices, severing all network traffic dependent on…

How to fix or mitigate CVE-2026-20270?

Within 24 hours: contact Cisco TAC to confirm patch timeline for your affected IOS XE versions and request interim guidance; inventory all network devices running Cisco IOS XE by executing 'show version' on routers and switches to identify exposure. Within 7 days: implement network segmentation and access control lists restricting device access to trusted internal networks, enable IOS XE input validation and traffic rate limiting where available, and deploy continuous monitoring (NetFlow/SNMP) to detect exploitation attempts; prioritize internet-facing and core routing infrastructure. Within 30 days: test and deploy the vendor-released patch to all affected Cisco IOS XE devices starting with non-production environments; validate functionality and coordinate planned reboots with business stakeholders before deploying to production.

Cisco IOS XE CVE-2026-20270

EUVD-2026-53456 HIGH

Incorrect Calculation (CWE-682)

2026-08-05 cisco

GHSA-jmg2-f5xg-mf62

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

Network-reachable DoS with no auth or interaction needed; scope change reflects device-level crash disrupting all transit traffic beyond the process itself.

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 - 17:28 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-2026-20270 are related to incorrect calculation issues that are grouped under the Common Weakness Enumeration (CWE) Pillar CWE-682.

AnalysisAI

Denial-of-service conditions in Cisco IOS XE Software stem from multiple incorrect calculation flaws (CWE-682) discoverable over the network without authentication, capable of crashing the affected device and disrupting all traffic transiting it. The CVSS scope change (S:C) indicates impact extends beyond the vulnerable component itself, consistent with a network appliance crash affecting downstream routing and switching functions across an enterprise. Internally discovered and disclosed by Cisco as part of a proactive software hardening initiative, no public exploit identified at time of analysis and CISA KEV status is absent.

Technical ContextAI

Cisco IOS XE is the Linux-based operating system powering Cisco's enterprise routing and switching hardware platforms. CWE-682 (Incorrect Calculation) is a pillar-level weakness encompassing arithmetic errors, integer overflows, off-by-one conditions, and similar computational mistakes in software logic. In the context of a network operating system like IOS XE, such errors in packet-processing or protocol-handling code paths can cause process crashes or device reloads when malformed or edge-case inputs are processed. The CVSS vector AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H reflects that these calculation errors are reachable via the network without any credentials or user interaction, and the Changed Scope designation indicates the failure cascades beyond a single process to affect the entire device's operational availability, impacting all transit traffic. The CPE cpe:2.3:a:cisco:cisco_ios_xe_software:*:*:*:*:*:*:*:* confirms the vulnerability class covers the IOS XE software package broadly across platform variants.

RemediationAI

The primary remediation is to upgrade to a Cisco-released fixed version identified in the software hardening advisory at https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-hardening-iosxe-V8NMuMZJ. Exact fixed version numbers by software train are not enumerated in the available intelligence data and must be obtained directly from the advisory's fixed software table. As a compensating control where immediate patching is not feasible, restricting network-level access to affected devices using infrastructure ACLs or control plane policing (CoPP) to limit which source addresses can reach IOS XE services reduces the exposed attack surface - note this does not eliminate risk if the vulnerable code path is reachable via standard data-plane processing rather than the management plane. Enabling Cisco's Flexible NetFlow or similar telemetry to detect anomalous traffic patterns toward device control planes can support early detection. Organizations should prioritize patching on Internet-edge or perimeter devices where untrusted network access (AV:N/PR:N) is most directly applicable.