CVE-2026-75828 in Grav
Summary
by MITRE • 08/18/2026
Grav before 2.0.15 contains a stored cross-site scripting vulnerability in the detectXss() function where unpaired quotes in unquoted attribute values bypass event-handler detection. Authenticated editors can inject event handlers like onerror= that pass validation and execute in visitor browsers when page content is rendered.
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Analysis
by VulDB Data Team • 08/18/2026
The security flaw identified in Grav versions prior to 2.0.15 represents a significant stored cross-site scripting vulnerability rooted in the application's input sanitization logic, specifically within the detectXss function. This component is designed to scan user-supplied data for malicious patterns before storing it or rendering it on web pages. The core technical deficiency lies in how the parser handles unquoted attribute values that contain unpaired quotes. In standard HTML parsing and security filtering mechanisms, event handlers such as onload, onclick, or onerror are typically detected by looking for specific keyword prefixes followed by an equals sign within quoted attributes. However, this implementation fails to account for edge cases where a quote character is present but not properly paired or closed in the attribute value structure. This oversight allows attackers to craft payloads that appear syntactically valid enough to bypass the initial regex-based detection rules while still being interpreted as executable JavaScript by modern web browsers during rendering.
From an operational perspective, this vulnerability enables authenticated users with editor privileges to inject persistent malicious scripts into the content managed by the Grav platform. Because the attack vector is stored rather than reflected, the impact extends beyond a single session or request. When other visitors access pages containing the compromised content, their browsers will execute the injected event handlers automatically. This persistence transforms what might otherwise be a limited phishing opportunity into a widespread compromise mechanism. An attacker can leverage this to steal user sessions via cookie theft, perform actions on behalf of victims such as changing account settings or publishing malicious content, or redirect users to phishing sites designed to harvest credentials. The ability to bypass validation through unpaired quotes demonstrates a critical gap in the application's defense-in-depth strategy regarding input normalization and context-aware output encoding.
This vulnerability aligns with CWE-79, which classifies improper neutralization of input during web page generation as cross-site scripting. Furthermore, from an offensive security framework perspective, this behavior corresponds to techniques found in MITRE ATT&CK under the Execution category, specifically relating to client-side script injection via stored payloads. The exploitation relies on the trust relationship between the application and its authenticated users, highlighting a risk associated with insufficient privilege separation or overly permissive content editing capabilities for lower-privileged roles like editors who should not be able to inject executable code into public-facing views.
To mitigate this vulnerability, organizations running Grav versions earlier than 2.0.15 must apply the official patch immediately. The update addresses the logic error in the detectXss function by enhancing the parsing rules to correctly identify and neutralize event handlers even when they appear within unquoted or partially quoted attribute contexts. In addition to updating the software, administrators should review their access control policies to ensure that only trusted users with a need-to-know basis are granted editor privileges capable of modifying page content. Implementing a Content Security Policy header can also provide an additional layer of defense by restricting the sources from which scripts can be loaded and executed, thereby reducing the impact if similar vulnerabilities exist in other components or future releases. Regular security audits and static code analysis focused on input validation logic are recommended to prevent recurrence of such sanitization bypasses.