CVE-2026-20711 is a cross-site scripting vulnerability identified in the E-mail function of Cybozu Garoon versions 5.0.0 through 6.0.3. Cybozu Garoon is a groupware and collaboration platform widely used in enterprise environments. The vulnerability arises because the application fails to properly sanitize or encode user-supplied input within the email functionality, allowing an attacker to inject malicious scripts. When a victim user interacts with the crafted email content, the malicious script executes in their browser context. This XSS flaw can be leveraged to perform unauthorized actions, notably resetting arbitrary users’ passwords without requiring authentication. The CVSS v3.0 base score of 6.5 reflects a medium severity, with the vector indicating network attack vector (AV:N), low attack complexity (AC:L), no privileges required (PR:N), but user interaction needed (UI:R), unchanged scope (S:U), no confidentiality impact (C:N), high integrity impact (I:H), and no availability impact (A:N). No public exploits are known at this time, but the vulnerability poses a significant risk due to the ability to compromise user accounts and potentially gain unauthorized access to sensitive organizational data. The vulnerability was published on February 2, 2026, with the Japanese Computer Emergency Response Team (JPCERT) as the assigner. The lack of available patches at the time of disclosure necessitates immediate attention to alternative mitigations. The vulnerability’s exploitation could lead to account takeover, undermining the integrity of user credentials and organizational security policies.

For European organizations, the impact of CVE-2026-20711 could be substantial, especially for enterprises relying on Cybozu Garoon for internal communication and collaboration. Successful exploitation allows attackers to reset user passwords, potentially leading to unauthorized access to sensitive corporate information, disruption of business processes, and lateral movement within the network. This could result in data breaches, intellectual property theft, or sabotage of organizational operations. Given the medium severity and the requirement for user interaction, the risk is heightened in environments with less stringent email security policies or where users are not adequately trained to recognize phishing attempts. The integrity of user accounts is directly compromised, which may also affect compliance with European data protection regulations such as GDPR if personal data is exposed or manipulated. Organizations with high-value targets or critical infrastructure components integrated with Cybozu Garoon are at increased risk of targeted attacks leveraging this vulnerability.

1. Apply official patches from Cybozu as soon as they become available to remediate the vulnerability at the source. 2. Until patches are released, implement strict input validation and output encoding on all email content processed by Cybozu Garoon to prevent script injection. 3. Employ web application firewalls (WAFs) with custom rules to detect and block XSS payloads targeting the email function. 4. Restrict or disable HTML content rendering in emails within the platform to reduce attack surface. 5. Conduct user awareness training focusing on phishing and social engineering risks, emphasizing caution when interacting with unexpected or suspicious emails. 6. Monitor logs and user activities for unusual password reset requests or account changes to detect potential exploitation attempts. 7. Enforce multi-factor authentication (MFA) on user accounts to mitigate the impact of compromised credentials. 8. Segment networks and limit access rights to reduce lateral movement opportunities if an account is compromised. 9. Regularly review and update security policies related to email handling and collaboration tools.