An attacker exploited a previously unknown and unpatched Cisco vulnerability earlier this year to infiltrate a communications service provider and gain the highest level of access possible, Mandiant said Wednesday.

Cisco has since patched the flaw, one of seven actively exploited zero-day vulnerabilities this year in its SD-WAN (software-defined wide area network) software used to manage internet traffic within organizations, typically those that are widely distributed, such as banks with numerous branches.

But Google-owned cybersecurity firm Mandiant said the attacker (or attackers) could have used its root-level access to obtain broad and undetected visibility into the internal traffic throughout the provider’s entire corporate network. In a caveat, Mandiant also said it could not fully assess how far the compromise actually went because of how cleverly the perpetrators hid their activity.

The attack illustrated hackers’ ongoing targeting of edge devices, Mandiant said. Attacks on such devices have been very common and involved in some of the most consequential breaches in recent years, prompting the Cybersecurity and Infrastructure Agency to direct federal agencies to give them special attention this year.

“This campaign underscores the living off the edge paradigm, where threat actors prioritize the compromise of network appliances to bypass traditional security perimeters,” Mandiant wrote in a blog post. “As organizations increasingly adopt software-defined networking, the orchestrators managing these environments become primary targets. These devices offer a black box environment for threat actors: they often lack the telemetry required for deep forensic analysis, and their role as a central control plane provides a stealthy platform for persistent, wide-scale access to internal enterprise traffic.”

Mandiant didn’t attribute the attack to any specific group, citing the work the attacker did to cover their tracks and delete evidence. But it noted that “for state-sponsored actors, the ability to exploit zero-day vulnerabilities in these platforms remains a premier vector for long-term strategic intelligence collection.”

Kelli Vanderlee, senior manager for Google Threat Intelligence Group, told CyberScoop that “exploiting zero day vulnerabilities in edge devices and the extensive anti-forensic activities are consistent with previously documented cyber espionage threat actor behavior.”

The company also didn’t name the victim service provider.

The attacks on the service provider came in two waves. The first activity Mandiant observed from late 2025 to early 2026 exploited one of two then-unpatched vulnerabilities (CVE-2026-20127 or CVE-2026-20182), with the attacker making unauthorized “peering” connections to the victim’s SD-WAN Manager devices in a kind of digital handshake to verify identity and trust.

Once there, the attacker facilitated its access and used it to manipulate default account passwords in hopes of avoiding detection. Next, the attacker exploited the zero-day vulnerability (CVE-2026-20245) in Cisco Catalyst SD-WAN Manager, activity Mandiant observed in March, and created a rogue user account, “troot” that gave full root-level control.

“On June 4, 2026, Cisco published a security advisory about a privilege escalation vulnerability in Cisco Catalyst SD-WAN Manager,” a Cisco spokesperson said. “Cisco strongly recommends customers upgrade to a fixed software release as outlined in the advisory.”

Updated 6/24/26: to include Cisco comment.

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Cisco customers are confronting yet another actively exploited zero-day vulnerability affecting the vendor’s SD-WAN management software, reinforcing pressure on organizations that have experienced rare breaks from active threats this year.

The vulnerability — CVE-2026-20245 — marks the seventh actively exploited zero-day in Cisco SD-WANs this year.

Cisco said it first became aware of active exploitation of the latest defect in the network management software earlier this month. The company disclosed the vulnerability, which was first spotted by Mandiant, on Thursday and warned that a security patch is not yet available and there are no workarounds to mitigate the defect in the meantime.

“A patch for this vulnerability will be provided on a future date,” a company spokesperson said in a statement. 

Cisco did not attribute the attacks to any specific group, describe the objectives of those attacks or share how many organizations have already been impacted.

The validation error defect affecting the Cisco Catalyst SD-WAN Manager allows authenticated or local attackers to execute commands as root, resulting in command-injection attacks on an affected system, the company said.

Yet, the scope of potential impact may be limited because exploitation requires valid credentials or privileged access through other means. Cisco said exploitation of a pair of zero-days it disclosed earlier this year —  CVE-2026-20182 or CVE-2026-20127 — could allow attackers the access required to exploit the new vulnerability. 

The company said it is “not aware of successful exploitation by other means,” adding that it “observed limited cases where the exploitation of this bug resulted in a configuration change pushed to edge devices.”

Landon Rice, senior exploit developer at VulnCheck, said the need for existing privileges “makes an attacker heavily reliant on previous vulnerabilities, or a net-new initial access vector, in order to be able to reach the privilege escalation path.”

Cisco advised customers to upgrade to fixed software released in May as part of its response to CVE-2026-20182 as a protective measure. 

Absent a patch that would provide organizations more protection against the new vulnerability, Cisco provided some indicators of compromise but noted that those same log entries may occur during standard operations. The company encouraged customers that need help distinguishing between legitimate and malicious activity to contact Cisco Technical Assistance Centers.

Cisco isn’t the only security vendor facing an onslaught of attacks on its customers, but it is among the most heavily targeted. The Cybersecurity and Infrastructure Security Agency has added seven vulnerabilities affecting Cisco SD-WANs and firewalls to its known exploited vulnerabilities catalog this year, not including CVE-2026-20245, which has yet to be added to the catalog.

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