Attack Chain

1. An attacker identifies a Grav API endpoint susceptible to the ?token= parameter vulnerability.
2. A valid JWT admin access token for the Grav API is acquired through passive means (e.g., from web server access logs, browser history, proxy/CDN logs, or HTTP Referer header leakage).
3. The attacker constructs a malicious HTTP request to a Grav API endpoint, embedding the leaked JWT token in the ?token= URL query parameter.
4. The Grav API processes the request, authenticating the attacker with the legitimate admin token.
5. The attacker proceeds to read sensitive configuration and user data from the Grav system via authenticated API calls.
6. Utilizing API functionality, the attacker creates new administrative user accounts to establish persistence within the Grav environment.
7. The attacker modifies critical system settings or configuration parameters via API calls to further control the application.
8. Finally, the attacker deletes content, such as pages, or performs other destructive actions, achieving unauthorized control and data manipulation within the Grav instance.

Impact

The successful exploitation of CVE-2026-62386 can lead to severe consequences for affected Grav instances. Unauthorized individuals gaining access to valid admin JWT tokens can bypass authentication mechanisms and achieve full control over the Grav API. This can result in the complete compromise of data confidentiality through the reading of sensitive configuration and user data, including potentially private content. Furthermore, the ability to create new administrator accounts and modify system settings grants attackers persistent access and potential privilege escalation, allowing them to subvert the website's functionality and integrity. The deletion of pages represents a direct impact on data availability and can lead to significant reputational damage or operational disruption.

Recommendation

• Patch CVE-2026-62386 immediately by upgrading the Grav API plugin to version 1.0.0-rc.16 or higher.
• Review web server access logs, proxy logs, and CDN logs for any instances of ?token= parameters in URL paths, which could indicate prior or ongoing token exposure.
• Configure web server logging to filter or redact sensitive URL query parameters (specifically token=) to prevent future leakage, even after patching.
• Deploy the Sigma rule provided in this brief to your SIEM to detect attempts to exploit this vulnerability or unusual token usage patterns.