CVE-2025-61931 is a stored cross-site scripting vulnerability identified in Implem Inc.'s Pleasanter software, specifically affecting versions 1.4.20.0 and earlier. The vulnerability resides in the Body, Description, and Comments fields where user-supplied input is not properly sanitized or encoded before being stored and subsequently rendered in other users' browsers. This flaw allows an attacker with at least limited authenticated access to inject malicious JavaScript code that executes when a logged-in user views the affected content. The attack vector is network-based, requiring the attacker to submit crafted input and rely on victim interaction to trigger the script execution. The vulnerability impacts confidentiality and integrity by enabling theft of session tokens, user credentials, or performing unauthorized actions on behalf of the victim. Availability is not impacted. The CVSS v3.0 base score of 5.4 reflects the medium severity, considering the low attack complexity but requiring privileges and user interaction. No public exploits are currently known, but the vulnerability poses a risk especially in environments where Pleasanter is used for collaboration or sensitive information management. The vulnerability was published on October 24, 2025, and no official patches or mitigations have been linked yet. The flaw highlights the importance of secure coding practices such as input validation and output encoding to prevent XSS in web applications.

For European organizations, this vulnerability could lead to unauthorized disclosure of sensitive information, session hijacking, and potential privilege escalation within the Pleasanter application. Since Pleasanter is often used for project management and collaboration, exploitation could compromise business workflows and confidential data. The requirement for authenticated access limits the attack surface but insider threats or compromised accounts could be leveraged. The integrity of data could be undermined by unauthorized script execution, potentially enabling attackers to manipulate content or perform actions on behalf of users. Although availability is not directly affected, the resulting trust erosion and potential data breaches could have regulatory and reputational consequences, especially under GDPR. Organizations in sectors such as finance, government, and critical infrastructure using Pleasanter are particularly at risk due to the sensitivity of their data and regulatory scrutiny.

European organizations should implement the following specific mitigations: 1) Immediately audit and restrict user privileges in Pleasanter to the minimum necessary, reducing the risk of malicious input submission. 2) Apply strict input validation and output encoding on the Body, Description, and Comments fields to neutralize malicious scripts; if the vendor has not released patches, implement web application firewall (WAF) rules to detect and block common XSS payloads targeting these fields. 3) Monitor logs for unusual activity or repeated input of suspicious scripts. 4) Educate users about the risks of clicking on untrusted links or content within Pleasanter. 5) Segregate Pleasanter instances from critical networks to limit lateral movement if exploitation occurs. 6) Engage with Implem Inc. for timely patching and verify updates before deployment. 7) Consider deploying Content Security Policy (CSP) headers to restrict script execution sources. These targeted steps go beyond generic advice by focusing on the specific vulnerable components and operational context of Pleasanter.