CVE-2025-58070 is a stored cross-site scripting (XSS) vulnerability identified in the Pleasanter product by Implem Inc., affecting versions 1.4.20.0 and earlier. The vulnerability resides specifically in the Preview for Attachments functionality, where an attacker can embed malicious JavaScript code within an attachment preview. When a logged-in user accesses the preview, the malicious script executes in their browser context, potentially allowing the attacker to steal session tokens, perform actions on behalf of the user, or manipulate displayed data. The vulnerability does not require prior authentication, but user interaction is necessary to trigger the script execution. The CVSS 3.0 base score of 6.1 reflects a medium severity, with an attack vector over the network, low attack complexity, no privileges required, but requiring user interaction. The impact affects confidentiality and integrity but not availability. No known exploits have been reported in the wild, and no official patches have been released at the time of publication. The vulnerability is significant because stored XSS can persist across sessions and affect multiple users, increasing the attack surface. The scope is limited to users of vulnerable Pleasanter versions who preview attachments, making it a targeted but impactful threat. The vulnerability was published on October 24, 2025, and assigned by JPCERT.

For European organizations, this vulnerability poses a risk primarily to the confidentiality and integrity of user data within Pleasanter environments. Attackers exploiting this XSS flaw could hijack user sessions, steal sensitive information, or perform unauthorized actions under the victim's identity. This could lead to data breaches, unauthorized data modification, or lateral movement within the affected organization's network. Since Pleasanter is a collaborative platform, the compromise of one user could impact multiple users and business processes. The absence of availability impact reduces the risk of service disruption but does not diminish the potential damage from data exposure or manipulation. Organizations relying on Pleasanter for critical workflows or sensitive data management are particularly at risk. The lack of known exploits in the wild provides a window for proactive mitigation. However, the ease of exploitation (no authentication needed, low complexity) means attackers could quickly develop exploits once the vulnerability becomes widely known. European entities with regulatory requirements around data protection (e.g., GDPR) must consider the compliance implications of potential data leakage or unauthorized access resulting from this vulnerability.

1. Immediately restrict or disable the Preview for Attachments feature in Pleasanter until a patch is available. 2. Implement strict input validation and output encoding on all attachment previews to sanitize any embedded scripts. 3. Employ Content Security Policy (CSP) headers to limit the execution of unauthorized scripts within the application context. 4. Educate users to avoid opening suspicious attachments or previews from untrusted sources. 5. Monitor application logs and user activity for unusual behavior indicative of XSS exploitation attempts. 6. Isolate the Pleasanter environment within segmented network zones to reduce lateral movement risk. 7. Regularly update Pleasanter to the latest version once patches addressing this vulnerability are released. 8. Conduct security testing focused on XSS vectors in the application to identify any additional injection points. 9. Use web application firewalls (WAFs) with rules tailored to detect and block XSS payloads targeting the attachment preview feature. 10. Coordinate with Implem Inc. for timely patch deployment and vulnerability disclosure updates.