Zero-Day Exploitation of Vulnerability (CVE-2026-20245) in Cisco Catalyst SD-WAN Manager

Introduction 

In early 2026, Mandiant identified a threat actor targeting SD-WAN infrastructure at a service provider. After gaining initial access, the threat actor exploited a zero-day vulnerability (CVE-2026-20245) in Cisco Catalyst SD-WAN to escalate privileges from a compromised administrative account to root-level access.

The vulnerability stems from the device’s file upload feature lacking the ability to properly filter malicious data.

Throughout the intrusion, to maintain operational security and avoid detection, the threat actor consistently employed anti-forensic techniques, selectively deleting and restoring system configuration files that were modified during their activities.

Key Observations

• Rogue Peering and Credential Manipulation: In March 2026, a threat actor established initial access via unauthorized peering connections to facilitate Secure Shell (SSH) access. The threat actor used that access to manipulate default account passwords to evade detection.

• Exploitation of CVE-2026-20245: Subsequently, the attacker leveraged a zero-day privilege escalation vulnerability (now tracked as CVE-2026-20245) in Cisco Catalyst SD-WAN Manager to gain root-level access via a malicious CSV upload.

• Extensive Anti-Forensic Cleanup: The threat actor deleted malicious files, reverted configuration changes, and executed a validation script to ensure indicators are purged.

What is SD-WAN?

Traditional Wide Area Networks (WANs) rely heavily on physical, proprietary hardware routers to direct traffic. This model is often rigid, complex to scale, and struggles to handle the demands of modern cloud computing.

Software-Defined Wide Area Network (SD-WAN) solves this by decoupling the network’s management and control logic from the underlying physical hardware. Instead of configuring individual routers one by one, a centralized software controller is used to orchestrate the entire network from a single dashboard. SD-WANs are typically used by highly distributed organizations, such as banks, retail corporations, technology services, and healthcare providers, to securely connect multiple remote branch locations directly to central cloud services.

What is Peering?

Within an SD-WAN fabric, peering is the logical process of establishing a trusted, authenticated relationship between distinct network components, such as edge routers, regional hubs, and central controllers.

Before any data can be securely transmitted across the network fabric, these devices must perform a digital handshake. During the peering phase, devices mutually authenticate each other using cryptographic certificates. Once identity and trust are verified, they exchange underlying routing tables and automatically build secure tunnels to facilitate safe data transport. 

Additional Vulnerabilities in Cisco Catalyst SD-WAN Controllers

CVE-2026-20127 and CVE-2026-20182 are critical vulnerabilities recently disclosed by Cisco that affect the peering authentication mechanism for Cisco Catalyst SD-WAN controllers. Both vulnerabilities could allow an unauthenticated, remote attacker to bypass authentication and obtain administrative privileges.

Intrusion Campaign Overview

Initial Access Via Rogue Peering Connections

From late 2025 to January 2026, Mandiant observed multiple unauthorized peering connections to the victim’s SD-WAN Manager devices. It is possible that these connections occurred due to the exploitation of CVE-2026-20127 or CVE-2026-20182 as the vulnerabilities were not disclosed, and patches were not available during this period.

Beginning in March 2026, further unauthorized peering connections were seen on a device running a software version unaffected by CVE-2026-20127. However, Cisco confirmed that these connections did not leverage CVE-2026-20182 either, and could instead be using stolen certificate material from a previous compromise of the same device.

It is unclear if the same threat actor was responsible for the late 2025 to January 2026 and March 2026 rogue peering activity. 

Successful Authentications By Altering The Admin Account Password

In March 2026, the threat actor established new rogue peer connections and successfully authenticated to the SD-WAN Manager device via SSH using the vmanage-admin account on the same victim devices.

Once authenticated via SSH, the threat actor executed commands to change the password of the default admin account. The threat actor authenticated directly to the SD-WAN Manager web application interface using the admin account and exfiltrated configurations of the SD-WAN fabric.