CVE-2026-20230, a server-side request forgery (SSRF) vulnerability affecting Cisco’s Unified Communications Manager (Unified CM), is being exploited to drop webshells and achieve remote code execution capability on the underlying server.

“Our honeypots are seeing automated sweeps dropping webshells, all via Tor,” threat intelligence firm Defused warned today, after observing initial attacks over the weekend.

The vulnerability

Cisco Unified Communications Manager is an enterprise-grade IP telephony and call processing platform. It’s typically deployed as a virtual machine, commonly on Cisco UCS servers running VMware ESXi.

CVE-2026-20230 was reported to Cisco by an independent security researcher working with SSD Secure Disclosure.

It stems from improper input validation for specific HTTP requests, and can be triggered by unauthenticated, remote attackers by sending a specially crafted HTTP request to a vulnerable instance.

“A successful exploit could allow the attacker to write files to the underlying operating system that could be used later to elevate to root, Cisco said on June 3, 2026, when it revealed the existence of the flaw and released patches for it.

At the time, the vendor confirmed the existence of a proof-of-concept (PoC) exploit for CVE-2026-20230, but said that they were “not aware of any malicious use of the vulnerability.”

A PoC is now public

The PoC they mentioned was likely the one published on Tuesday by the SSD Secure Disclosure technical team.

Knowing the target system’s hostname is a pre-requisite for leveraging the exploit, but that can easily be achieved by accessing a specific URL, they noted.

With the PoC now public, exploitation attempts by other threat actors are likely.

Earlier this year, attackers exploited CVE-2026-20045, a code injection vulnerability in Cisco enterprise communications products (including Unified Communications Manager), in zero-day attacks.

Customers who haven’t upgraded or aren’t able to upgrade to a fixed Cisco Unified Communications Manager or Cisco Unified Communications Manager Session Management Edition version are advised to mitigate the risk of exploitation by disabling the vulnerable WebDialer service.

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