CVE-2021-24637 in Google Fonts Typography Plugin
Summary
by MITRE • 09/20/2021
The Google Fonts Typography WordPress plugin before 3.0.3 does not escape and sanitise some of its block settings, allowing users with as role as low as Contributor to perform Stored Cross-Site Scripting attacks via blockType (combined with content), align, color, variant and fontID argument of a Gutenberg block.
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Analysis
by VulDB Data Team • 09/22/2021
The vulnerability identified as CVE-2021-24637 affects the Google Fonts Typography WordPress plugin version 3.0.2 and earlier, representing a critical stored cross-site scripting flaw that undermines the security of WordPress installations. This vulnerability specifically targets the plugin's handling of block settings within the Gutenberg editor, creating an attack vector that can be exploited by users possessing minimal privileges. The issue stems from insufficient input validation and output escaping mechanisms within the plugin's codebase, particularly when processing parameters related to typography blocks. Attackers can leverage this weakness to inject malicious scripts that persist within the WordPress database, making the vulnerability particularly dangerous as it can affect all users who view affected content.
The technical flaw manifests in the plugin's failure to properly sanitize and escape user-supplied parameters when rendering typography blocks within the Gutenberg interface. Specifically, the blockType, content, align, color, variant, and fontID arguments are processed without adequate security measures to prevent malicious input from being executed as scripts. This vulnerability falls under the CWE-79 category of Cross-Site Scripting, with the stored nature of the flaw meaning that malicious scripts are permanently embedded in the database rather than being reflected in a single request. The low privilege requirement of Contributor level access makes this vulnerability particularly concerning as it allows users who typically have limited capabilities to execute sophisticated attacks that could compromise other users or administrators.
The operational impact of this vulnerability extends beyond simple script execution, as it can enable attackers to perform session hijacking, defacement of content, data exfiltration, and potentially escalate privileges within the WordPress environment. The stored nature of the XSS means that every user who views affected pages becomes a potential victim of the malicious code execution, creating a wide attack surface. The vulnerability is particularly dangerous in multi-user environments where contributors might have access to the editor but should not possess the ability to inject persistent malicious code. This flaw can be exploited to manipulate the typography blocks that users see when editing content, potentially redirecting them to malicious sites or stealing their authentication cookies. The impact is amplified by the widespread adoption of the Google Fonts Typography plugin, which makes this vulnerability prevalent across numerous WordPress installations.
Mitigation strategies for CVE-2021-24637 should prioritize immediate plugin updates to version 3.0.3 or later, which includes proper input sanitization and output escaping mechanisms. Administrators should also implement additional security measures such as restricting contributor access to the Gutenberg editor or implementing Content Security Policy headers to limit script execution. Regular security audits of WordPress plugins and themes should be conducted to identify similar vulnerabilities, with particular attention to how user inputs are handled and rendered within the WordPress environment. The vulnerability demonstrates the importance of proper input validation and output escaping in web applications, aligning with ATT&CK technique T1213 for credential access through web application attacks. Organizations should also consider implementing web application firewalls and monitoring for suspicious script injection patterns, as well as maintaining comprehensive backup strategies to quickly recover from potential compromise scenarios. The incident underscores the critical need for security-conscious development practices and regular security assessments of third-party WordPress components to prevent similar vulnerabilities from being exploited in production environments.