Horizon Alert
Summary of the vulnerability and why it matters
This advisory concerns a stored cross-site scripting vulnerability in the Grav content management system. The flaw allows authenticated users with editing privileges to inject malicious code that can execute within the browsers of website visitors when content is displayed. This could potentially lead to various malicious actions, impacting user trust and data integrity.
- Authenticated editors can run code in visitor browsers.
- It affects how public websites present content securely.
- Confirm relevance and exposure for Grav installations.
Attack Path
How an attacker could exploit the issue
An attacker could exploit this vulnerability by leveraging their authenticated access as an editor within the Grav CMS. By injecting specially crafted code containing unpaired quotes into unquoted attribute values within page content, the attacker can bypass security checks in the `detectXss()` function. When a visitor views the compromised page content, the malicious script executes in their browser, potentially leading to further compromise.
- Entry condition: Authenticated editor access.
- Trigger point: Visitor viewing crafted page content.
- Resulting risk: Arbitrary script execution in browsers.
Live Threat
Current exploitation, exposure, and threat context
When supported by the advisory, authenticated editors could inject malicious code into page content that, when rendered, executes in visitor browsers. This could affect visitor browsers and potentially expose them to risks associated with the injected code.
- Visitor browser code execution.
- Malicious script injection via content editing.
- Unspecified risks to visitor browsers.
Operational Fix
Recommended remediation, mitigation, and detection steps
The Grav content management system's stored cross-site scripting vulnerability requires immediate attention from teams managing web applications and their content. The first step is to identify all Grav instances, determine their internet reachability and business criticality, and then locate the accountable owner for remediation planning. Coordination with the Grav vendor may be necessary if updates are managed externally or if specific patching guidance is required.
- Content owners and platform teams.
- Confirm Grav instance reachability and criticality.
- Plan risk-based remediation with vendor coordination.
