CVE-2026-23768 is a Server-Side Request Forgery (SSRF) vulnerability identified in NAVER's lucy-xss-filter, a security filter designed to prevent cross-site scripting (XSS) attacks. The vulnerability arises when either the ObjectSecurityListener or EmbedSecurityListener options are enabled, and an attacker crafts embed or object HTML tags with a src attribute that lacks a file extension. Under these conditions, the filter improperly processes the src attribute and triggers a server-side HEAD HTTP request to an arbitrary URL specified by the attacker. This SSRF flaw allows attackers to make the vulnerable server initiate HTTP requests to internal or external systems, potentially bypassing network access controls or firewall restrictions. The impact of such requests can include reconnaissance of internal services, access to sensitive metadata endpoints, or leveraging the server as a proxy for further attacks. The vulnerability affects versions of lucy-xss-filter before the commit identified as 7c1de6d, with no specific version range provided. No public exploits have been reported yet, and no CVSS score has been assigned. The vulnerability is categorized under CWE-918, which covers SSRF issues. The absence of a file extension in the src attribute is a key trigger, indicating that the filter's validation logic is insufficiently strict. This flaw highlights the risks of server-side components that process user-supplied URLs without proper validation or access controls. Since lucy-xss-filter is used to enhance web application security, its compromise ironically introduces a new attack vector that could undermine internal network security and confidentiality.

For European organizations, this SSRF vulnerability poses significant risks, especially for those deploying NAVER's lucy-xss-filter in web applications exposed to untrusted users or the internet. Exploitation could allow attackers to perform unauthorized internal network scans, access sensitive internal services such as databases, metadata endpoints, or administrative interfaces, and potentially exfiltrate confidential information. This could lead to data breaches, service disruptions, or facilitate lateral movement within corporate networks. Organizations in sectors with strict data protection regulations, such as finance, healthcare, and government, may face compliance violations if internal data is exposed. Additionally, SSRF can be a stepping stone for more complex attacks, including remote code execution or privilege escalation, if combined with other vulnerabilities. The lack of authentication requirements and the ease of triggering the vulnerability increase the risk profile. Although no known exploits exist currently, the potential impact on confidentiality and availability is high, warranting urgent attention from affected entities.

To mitigate CVE-2026-23768, organizations should first identify all deployments of lucy-xss-filter within their environments. Since no official patch or fixed version is currently linked, the immediate step is to update the lucy-xss-filter component to the version including commit 7c1de6d or later, where the vulnerability is addressed. If updating is not immediately feasible, temporarily disable the ObjectSecurityListener and EmbedSecurityListener options, which are the vulnerable features triggering SSRF. Additionally, implement strict validation and sanitization of all embed and object tag src attributes, ensuring they include valid file extensions and conform to expected URL patterns. Employ network-level controls such as egress filtering and segmentation to limit the server's ability to make arbitrary outbound HTTP requests, reducing the impact of potential SSRF exploitation. Monitor server logs for unusual HEAD requests or unexpected outbound connections. Finally, incorporate SSRF detection mechanisms in web application firewalls (WAFs) and conduct regular security assessments focusing on SSRF vectors.