CVE-2025-20350 is a stack-based buffer overflow vulnerability identified in the web user interface component of Cisco Session Initiation Protocol (SIP) Software running on various Cisco IP phones, including the Desk Phone 9800 Series, IP Phone 7800 and 8800 Series, and Video Phone 8875. The flaw arises from improper handling of HTTP packets, where crafted input can overflow a buffer on the device, causing it to crash and reload, thereby triggering a denial-of-service (DoS) condition. The vulnerability is exploitable remotely without any authentication or user interaction, provided that the affected phone is registered to Cisco Unified Communications Manager and has the Web Access feature enabled. Since Web Access is disabled by default, exploitation requires that this feature be explicitly enabled, which may limit exposure but does not eliminate risk. The vulnerability affects a broad range of Cisco SIP software versions, spanning multiple major and minor releases, indicating a long-standing issue. The CVSS v3.1 base score is 7.5, reflecting high severity due to network attack vector, low attack complexity, no privileges required, no user interaction, and impact limited to availability (device reload causing DoS). No known exploits have been reported in the wild as of the publication date. The vulnerability does not allow for confidentiality or integrity compromise but can disrupt critical voice communication services by causing device unavailability. This could impact organizations relying on Cisco IP telephony infrastructure for daily operations. Cisco has not yet published patches or mitigation details, but disabling Web Access or restricting access to the management interface can reduce risk. Organizations should monitor Cisco advisories for updates and prepare to deploy patches promptly once available.

For European organizations, the primary impact of CVE-2025-20350 is the potential disruption of voice communication services due to denial-of-service conditions on affected Cisco IP phones. Many enterprises, government agencies, and critical infrastructure operators in Europe rely heavily on Cisco telephony solutions for internal and external communications. A successful exploit could cause phones to reload unexpectedly, interrupting calls and potentially degrading business operations, emergency response, and customer service. This could be particularly damaging in sectors such as finance, healthcare, public administration, and telecommunications, where reliable voice communication is essential. Additionally, widespread exploitation could lead to reputational damage and operational delays. Although the vulnerability does not allow data theft or device takeover, the availability impact alone can have significant operational consequences. The requirement that phones be registered to Cisco Unified Communications Manager and have Web Access enabled somewhat limits exposure, but organizations with these configurations remain at risk. Attackers could target exposed management interfaces from the internet or internal networks if proper segmentation and access controls are not in place. The lack of known exploits currently provides a window for proactive mitigation, but the ease of exploitation and high severity score indicate that rapid action is necessary to prevent future incidents.

1. Immediately verify if Web Access is enabled on any Cisco IP phones running affected SIP software versions; disable Web Access if it is not required, as it is disabled by default and disabling it removes the attack vector. 2. Restrict network access to the management interfaces of affected devices by implementing strict firewall rules and network segmentation to limit exposure to trusted administrative hosts only. 3. Monitor Cisco security advisories closely for the release of official patches or firmware updates addressing CVE-2025-20350 and plan for rapid deployment once available. 4. Conduct internal audits to identify all affected Cisco IP phones and their software versions to prioritize remediation efforts. 5. Employ intrusion detection/prevention systems (IDS/IPS) with updated signatures to detect and block attempts to exploit this vulnerability by monitoring for anomalous HTTP traffic targeting the phones. 6. Educate IT and security teams about this vulnerability to ensure awareness and readiness to respond to any incidents. 7. Consider isolating voice infrastructure from general corporate networks to reduce the attack surface. 8. Regularly back up configuration and maintain incident response plans specific to telephony infrastructure disruptions.