WordPress Relevanssi Plugin Stored XSS in Comment Content

The Relevanssi – A Better Search plugin for WordPress is vulnerable to Stored Cross-Site Scripting via Comment Content in all versions up to, and including, 4.28.3 due to insufficient input sanitization and output escaping. This makes it possible for unauthenticated attackers to inject arbitrary web scripts in pages that will execute whenever a user accesses an injected page. This is only exploitable when the administrator has configured a non-empty value for the "Allowable tags in excerpts" setting, such as the default example value of <p><a><strong>, as the prefix-matching regex must have an allowable tag whose name is a prefix of the injected tag name.

Casky was already ahead

This CVE exploits attack patterns that Casky's 323matched skills already investigate — long before this vulnerability was disclosed. Claude's reasoning model maps these techniques to MITRE ATT&CK, so practitioners who ran these skills have already seen the threat behaviour in their findings.

Analysis

The Relevanssi – A Better Search plugin for WordPress contains a Stored Cross-Site Scripting (XSS) vulnerability affecting all versions up to 4.28.3. This vulnerability exists due to insufficient input sanitization and output escaping when processing comment content, particularly when administrators have configured non-empty values for the "Allowable tags in excerpts" setting. Unauthenticated attackers can exploit this flaw to inject malicious JavaScript that persists in the database and executes whenever users access affected pages. This poses a significant risk to WordPress sites using this popular search plugin, potentially compromising visitor sessions, stealing credentials, defacing content, or distributing malware to site users.

Casky's 323 matching skills leverage Claude AI with extended reasoning to detect the attack patterns associated with this vulnerability across MITRE ATT&CK techniques TA0001 (Reconnaissance) and TA0043 (Reconnaissance). Practitioners using the platform would identify suspicious patterns through detection of CWE-79 signature characteristics—specifically monitoring for improper neutralization of input during web page generation. The skills would flag comment submissions containing script tags or event handlers that bypass the plugin's excerpt tag allowance logic, analyze DOM-based payload structures, and correlate stored XSS indicators with comment metadata. Security teams would receive findings highlighting injection points in comment fields, unsafe output rendering in search excerpts, and stored payload persistence, enabling them to prioritize patching and implement Web Application Firewalls (WAF) rules to block malicious comment content before it reaches vulnerable plugin code.

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Casky Risk Score

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EPSS Probability

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Shodan Exposure

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GreyNoise Signal

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Composite risk scoring from EPSS, CISA KEV, Shodan, and GreyNoise — 21 security APIs correlated into a single Casky Risk Score. Coming in Casky Pro. Join early access →

323 Casky skills cover this attack pattern

These skills use Claude AI's reasoning model to surface findings in the same attack categories as CVE-2026-97641.

Abuse of Public-Facing API: Mobile API Abuse

mobile security · low

Run

abusing-dpapi-for-credential-access

red teaming · high

Run

abusing-shadow-credentials-for-privesc

red teaming · high

Run

MITRE ATT&CK Techniques

TA0001 TA0043

Investigate the attack patterns behind CVE-2026-97641

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