CVE-2025-58791 is a medium severity vulnerability classified as CWE-79, which corresponds to Improper Neutralization of Input During Web Page Generation, commonly known as Cross-site Scripting (XSS). This vulnerability affects the Arjan Olsder SEO Auto Linker plugin, specifically versions up to 1.5.3. The flaw allows an attacker to inject malicious scripts that are stored persistently within the application, leading to Stored XSS attacks. Stored XSS occurs when malicious input is saved by the application and later rendered in a web page without proper sanitization or encoding, enabling the execution of arbitrary JavaScript code in the context of the victim’s browser. The CVSS 3.1 base score is 5.9, indicating a medium severity level. The vector string (CVSS:3.1/AV:N/AC:L/PR:H/UI:R/S:C/C:L/I:L/A:L) reveals that the attack can be performed remotely over the network (AV:N) with low attack complexity (AC:L), but requires high privileges (PR:H) and user interaction (UI:R). The scope is changed (S:C), meaning the vulnerability affects resources beyond the security scope of the vulnerable component. The impact affects confidentiality, integrity, and availability at a low level. No known exploits are reported in the wild yet, and no patches are currently linked. The vulnerability arises from improper input validation and output encoding during web page generation, allowing malicious payloads to be stored and executed when other users access the affected pages. This can lead to session hijacking, defacement, or redirection to malicious sites.

For European organizations using the Arjan Olsder SEO Auto Linker plugin, this vulnerability poses a risk of client-side attacks that can compromise user sessions, steal sensitive data, or manipulate website content. Since SEO Auto Linker is typically used to automate internal or external linking on websites, exploitation could affect customer-facing portals, content management systems, or e-commerce platforms. The requirement for high privileges to inject the payload suggests that attackers would need to compromise or have access to an authorized user account, which limits the attack surface but does not eliminate risk, especially in environments with multiple administrators or editors. The stored nature of the XSS means that once injected, all visitors to the affected pages are at risk, potentially leading to widespread impact. Confidentiality and integrity of user data can be compromised, and availability may be affected if malicious scripts disrupt normal site operations. European organizations are subject to strict data protection regulations such as GDPR; exploitation leading to data leakage or unauthorized access could result in regulatory penalties and reputational damage.

Organizations should immediately audit their use of the SEO Auto Linker plugin and restrict administrative access to trusted personnel only. Since no official patches are currently available, temporary mitigations include disabling or removing the plugin until a fix is released. Implementing a Web Application Firewall (WAF) with rules to detect and block common XSS payloads can reduce risk. Additionally, applying Content Security Policy (CSP) headers to restrict script execution sources can mitigate the impact of injected scripts. Regularly scanning web applications for XSS vulnerabilities using automated tools and manual testing is recommended. Educate administrators and content editors about the risks of injecting untrusted content. Monitor logs for suspicious activity indicative of attempted exploitation. Once a patch is released by the vendor, prioritize timely deployment. Finally, ensure that all user inputs are properly sanitized and output is encoded according to context to prevent similar vulnerabilities.