CVE-2025-20351 is a cross-site scripting (XSS) vulnerability identified in the web user interface of several Cisco IP and video phone models running Cisco Session Initiation Protocol (SIP) Software. The affected devices include Cisco Desk Phone 9800 Series, IP Phone 7800 and 8800 Series, and Video Phone 8875. The root cause is improper neutralization of user-supplied input during web page generation, allowing an attacker to inject malicious scripts. An unauthenticated remote attacker can exploit this by persuading a user to click a crafted URL that triggers script execution within the context of the device’s web UI. This could lead to unauthorized access to sensitive information displayed in the browser or manipulation of the web interface session. Exploitation requires that the phone be registered to Cisco Unified Communications Manager and have Web Access enabled, which is off by default, reducing the attack surface. The vulnerability affects a wide range of Cisco SIP software versions spanning multiple releases, indicating a longstanding issue. The CVSS 3.1 base score is 6.1, with an attack vector of network (remote), low attack complexity, no privileges required, but user interaction is necessary. The scope is changed, indicating potential impact beyond the vulnerable component. No known exploits have been reported in the wild yet. The vulnerability highlights risks in unified communications infrastructure, where compromised devices could be leveraged for further network intrusion or data leakage. Cisco has not yet published patches or mitigation links, so organizations must rely on configuration changes and monitoring until updates are available.

For European organizations, this vulnerability poses a risk to the confidentiality and integrity of communications managed via Cisco SIP-enabled phones. Exploitation could allow attackers to steal sensitive information accessible through the phone’s web UI or hijack user sessions, potentially leading to further compromise of unified communications infrastructure. Organizations in sectors with high reliance on secure voice and video communications—such as government, finance, healthcare, and critical infrastructure—may face increased risk. The requirement for user interaction and Web Access being disabled by default somewhat limits the attack surface, but environments that enable Web Access for remote management are vulnerable. Successful exploitation could facilitate espionage, data leakage, or lateral movement within corporate networks. Additionally, compromised devices could be used as footholds for launching further attacks against internal systems. The broad range of affected software versions indicates many deployed devices may be vulnerable, especially in large enterprises and public sector organizations across Europe. The lack of known exploits reduces immediate urgency but does not eliminate the threat, as attackers may develop exploits once details become widely known.

1. Immediately verify if Web Access is enabled on Cisco SIP phones; disable it if remote web management is not essential, as it is disabled by default and disabling it removes the attack vector. 2. Monitor Cisco’s security advisories closely for patches or firmware updates addressing CVE-2025-20351 and apply them promptly once available. 3. Implement strict network segmentation to isolate SIP devices from general user networks and restrict access to their management interfaces to trusted administrators only. 4. Employ web application firewalls (WAFs) or intrusion prevention systems (IPS) capable of detecting and blocking XSS payloads targeting device web UIs. 5. Educate users about the risks of clicking unsolicited or suspicious links, especially those related to device management interfaces. 6. Audit and harden unified communications infrastructure configurations, ensuring minimal exposure of management interfaces to external or untrusted networks. 7. Enable logging and continuous monitoring of SIP device web UI access to detect anomalous activities indicative of exploitation attempts. 8. Consider deploying endpoint protection solutions that can detect script injection or unusual browser behaviors when accessing device web UIs.