Cisco Unified CM Flaw Exploited After PoC Reveals File-Write Path to Root

Ravie LakshmananJun 24, 2026Vulnerability / Network Security

Threat actors have begun to exploit a recently disclosed critical security flaw impacting Cisco Unified Communications Manager (Unified CM) and Unified Communications Manager Session Management Edition (Unified CM SME).

The vulnerability, tracked as CVE-2026-20230 (CVSS score: 8.6), is a case of improper input validation for specific HTTP requests that could allow an unauthenticated, remote attacker to conduct server-side request forgery (SSRF) attacks through an affected device.

“An attacker could exploit this vulnerability by sending a crafted HTTP request to an affected device,” Cisco said in an advisory released earlier this month. “A successful exploit could allow the attacker to write files to the underlying operating system that could be used later to elevate to root.”

In a post shared on X earlier this week, Defused Cyber said it observed active exploitation of the vulnerability in attacks. “This is currently being exploited from a single source using an unvetted PoC, with genuinely-formatted file:// file-write payloads landing on our decoys,” it noted.

However, for successful exploitation to occur, the WebDialer service must be enabled. It’s disabled by default. To check if the WebDialer is enabled, users can complete the following steps –

• Log in to the Cisco Unified CM Administration interface
• From the Navigation menu, choose Cisco Unified Serviceability and click Go
• From the Tools menu, choose Control Center – Feature Services
• In the CTI Services section of the page, check whether the current status of the Cisco WebDialer Web Service is Started or Not Running
• If the status is Started, WebDialer is enabled

The vulnerability has been patched in Unified CM and Unified CM SME versions 14SU6 and 15SU5. If immediate patching is not an option, it’s advised to disable the WebDialer service until a fix can be applied.

SSD Secure Disclosure has since published additional technical specifics of CVE-2026-20230, describing it as a flaw that allows unauthenticated attackers to arbitrarily write files in the server by leveraging the Webdialer component to obtain the true hostname of the target and ultimately achieve code execution.

Cisco has yet to update the advisory to reflect the exploitation status. Last week, the network security company released security updates for a medium-severity security flaw in Catalyst SD-WAN Manager (CVE-2026-20262, CVSS score: 6.5) that has come under active exploitation in the wild.