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CVE-2026-54239— FaustWP — Authentication Bypass via Initialization Vector Modification in Token Envelope

Quick assessment

Affected
wpengine faustjs
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Faust.js 是一款无头（headless）WordPress 工具包。在 1.8.11 版本之前，FaustWP WordPress 插件在其令牌信封（token envelope）中仅对密文进行身份验证，而在 文件的 和 函数中，未将 16 字节的初始化向量（Initialization Vector, IV）纳入 HMAC 校验范围。 已登录的非管理员用户若能从 接口获取授权码（authorization code），便可修改该未经认证的初始化向量，从而通过 CBC 解密机制改变令牌类型和用户标识符，同时

CVSS 8.8 · High

Possible ATT&CK Techniques 1 AI

T1190 · Exploit Public-Facing Application

Affected Version Matrix 1

VendorProduct Version RangeStatus
wpengine faustjs < 1.8.11 affected
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I. Basic Information for CVE-2026-54239

Vulnerability Information
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Vulnerability Title
FaustWP — Authentication Bypass via Initialization Vector Modification in Token Envelope
Source: CVE Program / CVE List V5
Vulnerability 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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
对数据真实性的验证不充分
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
wpengine faustjs < 1.8.11 -

II. Public POCs for CVE-2026-54239

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III. Intelligence Information for CVE-2026-54239

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Patches & Fixes for CVE-2026-54239 (2)

Vendor Advisories for CVE-2026-54239 (1)

IV. Related Vulnerabilities

Same vendor: wpengine
Same weakness: CWE-345

V. Comments for CVE-2026-54239

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