CVE-2021-24964 in LiteSpeed Cache Plugin
Summary
by MITRE • 01/03/2022
The LiteSpeed Cache WordPress plugin before 4.4.4 does not properly verify that requests are coming from QUIC.cloud servers, allowing attackers to make requests to certain endpoints by using a specific X-Forwarded-For header value. In addition, one of the endpoint could be used to set CSS code if a setting is enabled, which will then be output in some pages without being sanitised and escaped. Combining those two issues, an unauthenticated attacker could put Cross-Site Scripting payloads in pages visited by users.
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Analysis
by VulDB Data Team • 05/22/2025
The CVE-2021-24964 vulnerability affects the LiteSpeed Cache WordPress plugin version 4.4.3 and earlier, representing a critical security flaw that undermines the plugin's access control mechanisms. This vulnerability stems from insufficient validation of request origins within the plugin's architecture, specifically failing to properly authenticate that incoming requests originate from legitimate QUIC.cloud servers. The flaw manifests through the manipulation of the X-Forwarded-For HTTP header, which attackers can exploit to bypass authentication checks and gain unauthorized access to restricted endpoints. This type of vulnerability aligns with CWE-284 Access Control Issues, where improper access control allows unauthorized users to perform privileged actions.
The technical implementation of this vulnerability involves two interconnected components that together create a path for cross-site scripting attacks. The first component involves the bypass of server authentication checks through header manipulation, while the second component involves a dangerous configuration option that allows CSS code injection when specific settings are enabled. When combined, these flaws create a persistent threat where attackers can inject malicious payloads into web pages that will be executed in the context of users' browsers. The vulnerability specifically targets the plugin's handling of user-supplied data through the CSS code setting, which is then output without proper sanitization or escaping mechanisms. This represents a classic example of CWE-79 Cross-Site Scripting, where untrusted data is directly incorporated into web pages without adequate input validation or output encoding.
The operational impact of this vulnerability extends beyond simple data theft or service disruption to encompass full user session hijacking and potential privilege escalation within the WordPress environment. An unauthenticated attacker can leverage this vulnerability to inject malicious JavaScript code that will execute whenever users visit affected pages, potentially leading to cookie theft, session manipulation, or redirection to malicious sites. The attack surface is particularly concerning because it requires no prior authentication and can be exploited through standard web browser interactions. The vulnerability's exploitation is facilitated by the plugin's configuration options that enable CSS code injection, which when combined with the header bypass mechanism creates a persistent XSS vector. This aligns with ATT&CK technique T1566.001 Phishing, as the malicious payloads could be used to harvest user credentials or redirect them to phishing sites.
Mitigation strategies for CVE-2021-24964 must address both the authentication bypass and the XSS execution vectors simultaneously. The immediate solution involves upgrading to LiteSpeed Cache plugin version 4.4.4 or later, which includes proper server origin verification and enhanced input sanitization. Organizations should also implement additional network-level controls such as firewall rules that restrict access to plugin endpoints to trusted IP ranges and monitor for suspicious X-Forwarded-For header values. The security configuration should include disabling unnecessary CSS code injection settings when not required, as these create additional attack surfaces. Additionally, implementing Content Security Policy headers can provide defense-in-depth against XSS exploitation attempts, while regular security scanning of WordPress installations can help identify other potentially vulnerable plugins or themes. The vulnerability demonstrates the importance of proper input validation and access control implementation in web applications, particularly in CMS environments where plugins can significantly expand attack surfaces.