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CVE-2026-62386 – JWT Admin Token Leakage via URL Parameter – Grav API Plugin before 1.0.0-rc.16

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Summary

CVE-2026-62386 is a high-severity vulnerability (CVSS 8.2) classified as CWE-598 (Use of GET Request Method With Sensitive Query Strings), affecting the Grav CMS API plugin (getgrav/grav-plugin-api) in all versions before 1.0.0-rc.16. The plugin’s JwtAuthenticator::extractBearerToken() method accepts JWT admin access tokens via the ?token= URL query parameter across every API route, causing valid tokens to be persistently logged and leaked through multiple channels. An attacker who obtains a leaked token gains full unauthorized administrative API access to the affected Grav installation.

Technical details

  • Root cause: The JwtAuthenticator::extractBearerToken() fallback method accepts JWT access tokens via the ?token= URL query parameter on every API endpoint, rather than restricting token acceptance to secure HTTP headers. Any API call made using the query parameter method embeds the admin token directly in the URL.
  • Trigger conditions: Any API request authenticated via the ?token= query parameter — whether issued by an authorized user, an API client, or a frontend application — exposes the JWT token through standard HTTP infrastructure: it is logged verbatim in web server access logs, transmitted in the HTTP Referer header to third-party sites, stored in browser history, and captured by upstream proxy and CDN logs.
  • Attack vector: Network-accessible. An attacker with access to any of the above log sources or intermediary infrastructure can extract a valid admin token and replay it to make fully authenticated API calls without ever possessing the original credentials. The CVSS 4.0 vector reflects AT:P (Attack Requirements: Present) due to this indirect dependency.
  • Impact: A leaked token grants complete administrative API access, including reading system configuration and user data, creating new admin accounts, modifying system settings, and deleting pages — effectively constituting a full site compromise.

Affected software

  • getgrav/grav-plugin-api all versions from 0 through v1.0.0-rc.15 (all versions before 1.0.0-rc.16)

Severity

CVSS v3.1 base score: 7.5 (High)
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

Mitigation and recommended actions

  • Immediate: Upgrade the Grav API plugin to version 1.0.0-rc.16 or later. This release removes ?token= query parameter token acceptance and restricts JWT authentication exclusively to the Authorization: Bearer and X-API-Token HTTP headers.
  • If immediate patching is not possible: Disable or restrict external access to the API plugin routes (default path: /api/v1/) at the web server or network perimeter level. Additionally, audit existing web server access logs, proxy logs, and CDN logs for any occurrences of ?token= in API request URLs, and immediately revoke any JWT tokens found to be exposed.

IONIX Status

The IONIX research team is tracking ongoing exploitation attempts and recommends immediate patching. Potentially affected assets are outlined in this post.

References

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