Cisco zero-day under ongoing attack by persistent threat group

Attackers returned once again to a common target with a massive user base by exploiting a max-severity zero-day vulnerability affecting Cisco Catalyst SD-WAN Controller and Manager.

The threat group behind the “limited” number of attacks Cisco is aware of thus far are also linked to a series of previously disclosed vulnerabilities in the vendor’s firewalls and SD-WAN systems, the company said in a threat advisory Thursday.

The authentication bypass vulnerability — CVE-2026-20182 — has a CVSS rating of 10 and “behaves like a master key,” Douglas McKee, director of vulnerability intelligence at Rapid7, wrote in a blog post. 

“An attacker can present themselves to the controller as a trusted network router and, if the system accepts that claim without properly validating it, they can obtain the highest level of administrative access,” he added. “That is the cybersecurity version of a Jedi mind trick.”

Rapid7 discovered and reported the vulnerability to Cisco on March 9, and Cisco said it became aware of limited exploitation of the vulnerability earlier this month. The vendor disclosed and released a patch for the vulnerability Thursday, and the Cybersecurity and Infrastructure Security Agency quickly added the defect to its known exploited vulnerabilities catalog.

Cisco did not explain what occurred during that two-month window. Yet, the disclosure and warning from researchers marks another challenge for Cisco customers that have confronted a flood of actively exploited vulnerabilities affecting the vendor’s network edge software since late February. 

Cisco isn’t the only security vendor facing an onslaught of attacks on its customers, but it is among the most heavily targeted. CISA has added seven vulnerabilities affecting Cisco SD-WANs and firewalls to its known exploited vulnerabilities catalog in less than three months.

Cisco Talos researchers attributed the latest round of zero-day attacks to UAT-8616, the same attackers that exploited a pair of separate zero-days in Cisco’s network edge software for at least three years before the activity was discovered and reported in February. 

The company, which described the exploitation of the new zero-day as ongoing, once again declined to answer questions about the origins or motivations of UAT-8616. 

“We strongly recommend customers apply the available fixed software releases and follow the guidance provided in the advisories and Cisco Talos blog,” a spokesperson for the company said in a statement.

Cisco Talos researchers also warned that UAT-8616 and at least 10 other threat groups have chained together and achieved “widespread in-the-wild active exploitation of three vulnerabilities in unpatched Cisco Catalyst SD-WAN Infrastructure.” The company previously disclosed and released patches for the vulnerabilities — including CVE-2026-20122, CVE-2026-20128 and CVE-2026-20133 — in February. 

Rapid7 said it discovered the latest critical authentication bypass vulnerability when it was researching CVE-2026-20127, a previous zero-day the Five Eyes identified and confirmed as actively exploited by UAT-8616 in late 2025. Authorities and Cisco waited at least two months to disclose and patch the vulnerability, and share emergency mitigation guidance.

That campaign, which got underway at least three years prior, marked the second series of actively exploited zero-days in Cisco edge technology in less than a year. Both campaigns prompted CISA to issue emergency directives months after the attacks were first detected, and both attack sprees were underway for at least a year before they were discovered. 

The latest zero-day, which bypasses authentication in the same control-plane service as CVE-2026-20127,  requires no credentials or prior knowledge of the target environment for exploitation, Jonah Burgess, senior security researcher at Rapid7, told CyberScoop.

“Cisco confirmed it affects all deployment types, including on-premises, cloud, and FedRAMP environments. The SD-WAN Controller manages routing and policy for the entire overlay network, so a single compromised controller can potentially give an attacker influence over every branch, data center, and cloud edge connected to that fabric,” Burgess added.

His colleague at Rapid7, McKee, said attackers have become very good at turning weaknesses in central network infrastructure into high-impact operations. 

“Compromising one branch router is useful. Compromising the controller that manages the entire estate is a very different conversation. Now you are talking about the ability to reroute traffic, intercept communications, push malicious configuration, or simply break connectivity across the whole organization,” he wrote.

“That is the real paradox here,” McKee added. “The same architecture that gives defenders scale and simplicity can also give attackers a single point of catastrophic leverage.”