Overview
CVE-2025-66303 is a medium severity Denial of Service (DoS) vulnerability affecting Grav, a file-based web platform. Specifically, versions prior to 1.8.0-beta.27 are susceptible to a flaw that allows an attacker to render the administrative panel unusable by injecting malicious input into the scheduled_at parameter. This vulnerability arises from insufficient input sanitization when handling cron expressions, leading to a corrupted configuration and a non-functional admin interface.
Technical Details
The vulnerability lies in Grav’s handling of user-supplied input for scheduled tasks. The scheduled_at parameter, intended to define when a task should run based on a cron expression, lacks proper validation. An attacker can inject malicious characters, such as single quotes ('), into this parameter. This crafted input then corrupts the backup.yaml file, which stores scheduled task configurations. The result is a broken cron expression that prevents the admin panel from loading, effectively denying administrators access to essential management functions.
Recovery from this issue requires direct server access and manual modification of the backup.yaml file to correct the corrupted cron expression. This significantly disrupts administrative workflows and can lead to downtime.
CVSS Analysis
The Common Vulnerability Scoring System (CVSS) score for CVE-2025-66303 is 4.9 (Medium). The CVSS vector string is not provided in the initial data but would be something like: CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:L. This indicates:
- Attack Vector (AV): Network (N) – The vulnerability can be exploited remotely over the network.
- Attack Complexity (AC): Low (L) – Exploitation requires little specialized access or conditions.
- Privileges Required (PR): High (H) – The attacker needs administrative privileges to exploit the vulnerability.
- User Interaction (UI): None (N) – No user interaction is required for exploitation.
- Scope (S): Unchanged (U) – The vulnerability’s impact is limited to the affected component.
- Confidentiality Impact (C): None (N) – There is no impact on data confidentiality.
- Integrity Impact (I): None (N) – There is no impact on data integrity.
- Availability Impact (A): Low (L) – There is a denial of service.
Possible Impact
Exploitation of CVE-2025-66303 can have the following impacts:
- Denial of Service: The primary impact is the inability to access and manage the Grav admin panel. This disrupts content updates, configuration changes, and other essential administrative tasks.
- Downtime: The manual recovery process required to fix the corrupted
backup.yamlfile can lead to significant downtime for the affected Grav website. - Frustration and Inconvenience: System administrators will experience frustration and inconvenience due to the need to manually resolve the issue.
Mitigation and Patch Steps
The vulnerability is fixed in Grav version 1.8.0-beta.27. The recommended mitigation is to upgrade to this version or a later release as soon as possible.
- Upgrade Grav: Update your Grav installation to version 1.8.0-beta.27 or later. Refer to the official Grav documentation for instructions on upgrading.
- Verify Upgrade: After upgrading, verify that the vulnerability is resolved by attempting to inject malicious input into the
scheduled_atparameter and confirming that the admin panel remains functional.
If upgrading is not immediately feasible, consider implementing temporary workarounds, such as restricting access to the admin panel or implementing input validation on the scheduled_at parameter. However, these are not substitutes for a proper upgrade.
