CVE-2021-24964 is a medium-severity vulnerability affecting the LiteSpeed Cache WordPress plugin versions prior to 4.4.4. The core issue stems from improper verification of request origins, specifically failing to confirm that incoming requests are genuinely from QUIC.cloud servers. Attackers can exploit this by crafting requests with a specific X-Forwarded-For header value to access certain plugin endpoints. One such endpoint, when a particular setting is enabled, allows the injection of CSS code that is subsequently rendered on pages without proper sanitization or escaping. This combination enables an unauthenticated attacker to inject Cross-Site Scripting (XSS) payloads into pages viewed by users. The vulnerability is categorized under CWE-79, indicating a classic reflected/stored XSS flaw. The CVSS v3.1 base score is 6.1, reflecting a network attack vector with low attack complexity, no privileges required, but requiring user interaction (visiting the affected page). The scope is changed, meaning the vulnerability affects components beyond the initially vulnerable module. The impact primarily affects confidentiality and integrity by allowing script execution in the context of the victim’s browser, potentially leading to session hijacking, defacement, or redirection to malicious sites. Availability is not impacted. No known exploits in the wild have been reported, but the vulnerability presents a tangible risk to WordPress sites using the affected plugin versions, especially if the vulnerable CSS injection setting is enabled. The lack of patch links suggests users should upgrade to version 4.4.4 or later where the issue is fixed.

For European organizations, this vulnerability poses a moderate risk primarily to websites running WordPress with the LiteSpeed Cache plugin prior to version 4.4.4. Exploitation could lead to unauthorized script execution in users’ browsers, potentially compromising user data, stealing authentication tokens, or conducting phishing attacks via manipulated page content. Organizations relying on WordPress for customer-facing portals, e-commerce, or internal communication could see reputational damage and loss of user trust if exploited. Given the unauthenticated nature of the attack, threat actors can target any vulnerable site without needing credentials, increasing the attack surface. The requirement for user interaction (visiting a maliciously crafted page) means social engineering or phishing campaigns could be used to trigger the exploit. While availability is not affected, the confidentiality and integrity risks could lead to regulatory compliance issues under GDPR if personal data is compromised. The impact is heightened for organizations with high web traffic or those in sectors like finance, healthcare, or government where data sensitivity is paramount.

European organizations should immediately verify the version of the LiteSpeed Cache plugin deployed on their WordPress sites and upgrade to version 4.4.4 or later where the vulnerability is patched. If upgrading is not immediately feasible, disabling the vulnerable CSS injection setting within the plugin configuration is critical to prevent exploitation. Additionally, organizations should implement Web Application Firewalls (WAFs) with rules to detect and block suspicious X-Forwarded-For header manipulations and anomalous requests targeting the plugin endpoints. Regular security audits and scanning for XSS vulnerabilities on public-facing sites can help identify residual risks. User education to recognize phishing attempts is also advisable given the user interaction requirement. Monitoring web server logs for unusual request patterns involving the X-Forwarded-For header can provide early detection of exploitation attempts. Finally, applying Content Security Policy (CSP) headers can mitigate the impact of injected scripts by restricting script execution contexts.