CVE-2026-25916 is a vulnerability classified under CWE-420 (Unprotected Alternate Channel) affecting Roundcube Webmail versions before 1.5.13 and 1.6 before 1.6.13. The issue arises when the 'Block remote images' feature is enabled to prevent automatic loading of external images in emails, a common privacy and security measure. However, this protection does not extend to SVG feImage elements embedded within emails. SVG feImage is an SVG filter primitive that can reference external images, effectively bypassing the remote image blocking mechanism. This allows an attacker to embed malicious SVG content that loads external resources without user consent, potentially leaking user information such as IP addresses or other metadata through the unblocked SVG channel. The vulnerability has a CVSS v3.1 base score of 4.3 (medium severity), reflecting its network attack vector, low complexity, no privileges required, but requiring user interaction. The impact is limited to confidentiality as no integrity or availability impacts are noted. No patches or exploits are currently publicly available, but the vulnerability is published and should be addressed proactively. The vulnerability highlights a gap in the filtering logic of Roundcube Webmail's image blocking feature, which does not account for SVG-specific elements that can circumvent protections.

For European organizations, the primary impact is a potential confidentiality breach where attackers could track users or gather metadata by exploiting the SVG feImage bypass. This could undermine privacy policies and compliance with regulations such as GDPR, especially for organizations handling sensitive communications. While the vulnerability does not allow code execution or direct compromise of systems, the leakage of user information can facilitate targeted phishing or social engineering attacks. Organizations relying on Roundcube Webmail for internal or external communications may see increased risk of user tracking or data leakage. The absence of known exploits reduces immediate risk, but the widespread use of Roundcube in European hosting providers and enterprises means the vulnerability could be leveraged in the future. The medium severity rating suggests moderate urgency, but organizations should not delay remediation to maintain trust and compliance.

Organizations should upgrade Roundcube Webmail to versions 1.5.13 or 1.6.13 or later once patches are released to address this vulnerability. In the interim, administrators can consider disabling the 'Block remote images' feature if SVG content is not commonly used or implement additional email filtering rules to detect and block SVG attachments or embedded SVG content. Deploying advanced email security gateways that inspect and sanitize SVG elements can reduce risk. User awareness training should emphasize caution with emails containing SVG or other embedded content. Monitoring email logs for unusual SVG-related traffic or external resource requests can help detect exploitation attempts. Network-level controls to restrict outbound connections from mail clients to untrusted domains may also limit data leakage. Finally, organizations should review their privacy policies and incident response plans to incorporate potential confidentiality breaches via email.