CVE-2026-54239: wpengine faustjs

Vulnerability summary

CVE-2026-54239 is a high (CVSS 8.8) vulnerability in wpengine faustjs. EPSS estimates a 0.32% chance of exploitation in the next 30 days, higher than 24% of scored vulnerabilities.

Timeline

1. 17-09-2026
   PublishedVulnerability first disclosed.
2. 18-09-2026
   Last modifiedVulnerability information updated.

Description

Faust.js is a headless WordPress toolkit. Prior to 1.8.11, the FaustWP WordPress plugin authenticates only the ciphertext in its token envelope and excludes the 16-byte initialization vector from the HMAC in WPE\FaustWP\Auth\encrypt() and WPE\FaustWP\Auth\decrypt() in plugins/faustwp/includes/auth/functions.php. A logged-in non-administrator who obtains an authorization code from GET /generate can modify the unauthenticated initialization vector so that CBC decryption changes the token type and user identifier while the HMAC remains valid. This can produce an access token for an Administrator and permit full WordPress REST API access, administrator-account creation, plugin installation, and arbitrary code execution. This issue is fixed in repository version 1.8.11.

• CWE-345Insufficient Verification of Data AuthenticityThe product does not sufficiently verify the origin or authenticity of data, in a way that causes it to accept invalid data.
• CWE-639Authorization Bypass Through User-Controlled KeyThe system's authorization functionality does not prevent one user from gaining access to another user's data or record by modifying the key value identifying the data.