Stored XSS in Grav Media URL Fragment Rendering

Grav before 2.0.15 contains a stored cross-site scripting vulnerability in the audio and video media rendering through the sourceParsedownElement method. The media URL fragment is concatenated unescaped into rawHtml source elements, allowing attackers to inject arbitrary HTML and JavaScript that executes in viewers' sessions.

Casky was already ahead

This CVE exploits attack patterns that Casky's 322matched 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

Grav CMS versions before 2.0.15 suffer from a stored cross-site scripting (XSS) vulnerability in how media files are processed and rendered. When audio or video URLs are parsed through the sourceParsedownElement method, the URL fragments are directly concatenated into HTML without proper sanitization or encoding. This allows attackers to inject malicious JavaScript that persists in the content and executes whenever any user views the affected media—making this a particularly dangerous stored variant rather than a reflected attack. Organizations running vulnerable Grav installations, content creators, and their audiences are at risk of session hijacking, credential theft, and account takeover.

Casky's 322 matched skills leverage Claude's extended reasoning to map attack detection across MITRE ATT&CK's Initial Access (TA0001) and Persistence (TA0043) techniques. Practitioners using Casky would identify this threat through detection patterns that flag: (1) unsanitized user input flowing into HTML rendering contexts, (2) media URL parameters that bypass encoding validation, and (3) JavaScript execution within viewer sessions tied to persistent content storage. The platform's skill mapping helps security teams recognize that this CVE represents both an entry point for attackers and a persistence mechanism, since the malicious payload remains embedded in the content management system indefinitely. Detection would surface anomalous HTML/JS injection attempts in media metadata, unusual script execution during content rendering, and behavioral indicators consistent with post-exploitation activity following successful XSS execution.

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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 →

322 Casky skills cover this attack pattern

These skills use Claude AI's reasoning model to surface findings in the same attack categories as CVE-2026-75831.

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-2026-75831

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