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Vulnerability record · CVE-2026-54239 · published 17 September 2026

CVE-2026-54239: Insufficient verification of data authenticity vulnerability

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.

8.8 CVSS 3.1 High EPSS 0.32% · top 77.1% CWE-345 · Insufficient verification of data authenticityCWE-639 · Insecure direct object reference Awaiting Analysis
8.8CVSS 3.1 base score
0.32%EPSS exploitation probability, 30 days
NoNot in CISA KEV
0Affected product versions listed by NVD
3References
24 Sep 2026Last modified by NVD

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.

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

References

LinkTags
https://github.com/wpengine/faustjs/commit/cda00de7290f9b178cb1652d30b4cdf5bb8688d0
https://github.com/wpengine/faustjs/pull/2386
https://github.com/wpengine/faustjs/security/advisories/GHSA-q6pm-r77q-qcv3

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Source: NIST National Vulnerability Database (record CVE-2026-54239), CISA KEV, FIRST EPSS (scores of 2026-09-27). This page is refreshed as NVD updates the record.