CVE-2025-55996 identifies a medium-severity vulnerability in Viber Desktop version 25.6.0, specifically an HTML Injection flaw occurring via the 'text' parameter in the message compose/forward interface. This vulnerability is classified under CWE-79, which corresponds to Cross-Site Scripting (XSS) or similar injection issues involving untrusted HTML content. The flaw allows an attacker to inject arbitrary HTML code into messages composed or forwarded within the Viber Desktop client. When a user views or interacts with such a crafted message, the injected HTML could execute in the context of the application, potentially leading to unauthorized actions such as information disclosure, session hijacking, or manipulation of the user interface. The CVSS v3.1 base score is 6.3, indicating a medium severity level. The vector string (AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:L) shows that the attack can be launched remotely over the network without privileges, requires low attack complexity, no privileges, but does require user interaction (e.g., opening or forwarding a message). The impact affects confidentiality, integrity, and availability at a low level. No known exploits are currently reported in the wild, and no patches have been linked yet. The vulnerability affects the desktop client version 25.6.0, but specific affected versions beyond this are not detailed. The flaw's root cause is insufficient sanitization or validation of HTML content in the message text parameter, allowing injection of malicious HTML code.

For European organizations, the impact of this vulnerability can be significant, especially for enterprises and government entities that rely on Viber Desktop for internal or external communications. Exploitation could lead to leakage of sensitive information, such as contact lists, message contents, or authentication tokens, through injected scripts. Attackers could also manipulate message content to deceive users, potentially facilitating phishing or social engineering attacks. The integrity of communications could be compromised, undermining trust in the messaging platform. Availability impact is low but possible if injected code causes application crashes or denial of service. Since Viber is widely used in several European countries for personal and business communications, organizations using it without additional security controls may face increased risk of targeted attacks leveraging this vulnerability. The requirement for user interaction means social engineering tactics would likely be employed to trigger the exploit. The absence of known exploits in the wild suggests limited immediate risk, but the medium severity and ease of exploitation warrant proactive mitigation.

Organizations should immediately assess their use of Viber Desktop 25.6.0 and related versions. Since no official patch is currently available, users should be advised to exercise caution when receiving unexpected or suspicious messages, especially those containing links or unusual formatting. Implementing endpoint security solutions that can detect and block suspicious HTML or script injections within applications may help mitigate risk. Network-level protections such as filtering or sandboxing Viber traffic could reduce exposure. Administrators should monitor for updates from Viber and apply patches promptly once released. Additionally, user awareness training focused on recognizing social engineering attempts related to messaging platforms is critical. For organizations with strict security requirements, temporarily restricting or disabling Viber Desktop usage until a fix is available may be warranted. Logging and monitoring message activity for anomalies can aid in early detection of exploitation attempts.