Zero-day vulnerability in Catalyst SD-WAN Controller (formerly SD-WAN vSmart)

Improper authentication
CVE-2026-20127

Vulnerability details

Advisory: SB2026022553 - Authentication Bypass in Cisco Catalyst SD-WAN Controller

Vulnerable component: Catalyst SD-WAN Controller (formerly SD-WAN vSmart)

CVE-ID: CVE-2026-20127

CVSSv3 score: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H/E:H/RL:O/RC:C

CWE-ID: CWE-287 - Improper Authentication

Description:

The vulnerability allows a remote attacker to bypass authentication process.

The vulnerability exists due to an error in authentication mechanism. A remote non-authenticated attacker can send specially crafted requests to bypass authentication process and access NETCONF, which would then allow to manipulate network configuration for the SD-WAN fabric.

Note, the vulnerability is being actively exploited in the wild. 

External links:

https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-sdwan-rpa-EHchtZk

About zero-day vulnerabilities

Zero-day vulnerability is an undisclosed vulnerability in software that hackers can exploit to compromise computer programs, gain unauthorized access to sensitive data, penetrate networks, etc. We consider vulnerability a zero-day when there is no solution provided from software vendor and the vulnerability is being actively exploited by malicious actors.

Zero-day candidate is a potential zero-day vulnerability in software which might have been used in targeted attacks, however there is no evidence to support this suggestion.