The U.S.Cybersecurity and Infrastructure Security Agency (CISA) on Thursday added a newly disclosed vulnerability impacting Cisco Catalyst SD-WAN Controller to its Known Exploited Vulnerabilities (KEV) catalog, requiring Federal Civilian Executive Branch (FCEB) agencies to remediate the issue by May 17, 2026.

The vulnerability is a critical authentication bypass tracked as CVE-2026-20182. It’s rated 10.0 on the CVSS scoring system, indicating maximum severity.

“Cisco Catalyst SD-WAN Controller and Manager contain an authentication bypass vulnerability that allows an unauthenticated, remote attacker to bypass authentication and obtain administrative privileges on an affected system,” CISA said.

In a separate advisory, Cisco attributed the active exploitation of CVE-2026-20182 with high confidence to UAT-8616, the same cluster behind the weaponization of CVE-2026-20127 to gain unauthorized access to SD-WAN systems.

“UAT-8616 performed similar post-compromise actions after successfully exploiting CVE-2026-20182, as was observed in the exploitation of CVE-2026-20127 by the same threat actor,” Cisco Talos said. “UAT-8616 attempted to add SSH keys, modify NETCONF configurations, and escalate to root privileges.”

It’s assessed that the infrastructure used by UAT-8616 to carry out exploitation and post-compromise activities overlaps with Operational Relay Box (ORB) networks, with the cybersecurity company also observing multiple threat clusters exploiting CVE-2026-20133, CVE-2026-20128, and CVE-2026-20122 beginning March 2026.

The three vulnerabilities, when chained together, can allow a remote unauthenticated attacker to gain unauthorized access to the device. They were added to the CISA’s KEV catalog last month.

The activity has been found to leverage publicly available proof-of-concept exploit code to deploy web shells on hacked systems, allowing the operators to run arbitrary bash commands. One such JavaServer Pages (JSP)-based web shell has been codenamed XenShell owing to the use of a PoC released by ZeroZenX Labs.

At least 10 different clusters have been linked to the exploitation of the three flaws –

• Cluster 1 (Active since at least March 6, 2026), which deploys the Godzilla web shell
• Cluster 2 (Active since at least March 10, 2026), which deploys the Behinder web shell
• Cluster 3 (Active since at least March 4, 2026), which deploys the XenShell web shell and a variant of Behinder
• Cluster 4 (Active since at least March 3, 2026), which deploys a variant of the Godzilla webshell
• Cluster 5 (Active since at least March 13, 2026), which malware agent compiled off the AdaptixC2 red teaming framework
• Cluster 6 (Active since at least March 5, 2026), which deploys the Sliver command-and-control (C2) framework
• Cluster 7 (Active since at least March 25, 2026), which deploys an XMRig miner
• Cluster 8 (Active since at least March 10, 2026), which deploys the KScan asset mapping tool and Nim-based backdoor that’s likely based on NimPlant and comes with capabilities to perform file operations, execute files using bash, and collect system information
• Cluster 9 (Active since at least March 17, 2026), which deploys an XMRig miner and a peer-based proxying and tunneling tool called gsocket
• Cluster 10 (Active since at least Mar 13, 2026), which deploys a credential stealer that attempts to obtain an admin user’s hashdump, JSON Web Tokens (JWT) key chunks that are used for REST API authentication, and AWS credentials for vManage

Cisco is recommending that customers follow the guidance and recommendations outlined in the advisories for the aforementioned vulnerabilities to protect their environments.