EUVD-2026-58842
GHSA-r26j-82cg-5h6c
Severity by source
AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Remote unauthenticated request with predictable static crypto yields admin auth cookie, so PR:N/UI:N/AC:L and full C/I/A impact; scope unchanged within the WordPress app.
Primary rating from Vendor (Wordfence).
CVSS VectorVendor: Wordfence
Lifecycle Timeline
2DescriptionCVE.org
The User Session Synchronizer plugin for WordPress is vulnerable to Authentication Bypass leading to Account Takeover in all versions up to, and including, 1.4.0. The synchronize_session() function, hooked on init and therefore executed on every request, performs no nonce, capability, or shared-secret validation against the attacker-supplied ussync-key, ussync-token, and ussync-ref parameters; when ussync-key references an unregistered slot, get_option() returns false for both the secret key and the domain list, causing the AES-256-CBC encryption key to degrade to the fully predictable md5('') and the referer allowlist to collapse to an empty-string match, while the AES IV is unconditionally hard-coded as md5('another-secret'). This makes it possible for unauthenticated attackers to supply a crafted request encrypting any known or guessable user email address in the ussync-ref parameter, causing the handler to call wp_set_auth_cookie() for the matched user and granting full authentication as that user - including administrators - with no prior knowledge of site secrets.
Articles & Coverage 1
AnalysisAI
Authentication bypass and full account takeover in the User Session Synchronizer WordPress plugin (versions ≤1.4.0) lets unauthenticated attackers log in as any user, including administrators, by abusing the init-hooked synchronize_session() handler. Because an unregistered ussync-key slot makes get_option() return false, the AES-256-CBC key silently degrades to the predictable md5('') and the referer allowlist collapses to an empty match, while the IV is hard-coded, so an attacker who knows or guesses a target email can forge a valid ussync-ref token. No public exploit is identified at time of analysis and the flaw is not in CISA KEV, but the CVSS 9.8 rating and trivial cryptographic prerequisites make weaponization straightforward.
Technical ContextAI
The vulnerability lives in a WordPress plugin (CPE cpe:2.3:a:rafasashi:user_session_synchronizer) that is designed to synchronize logged-in sessions across multiple sites/domains by passing encrypted tokens between them. The root cause is CWE-287 (Improper Authentication): synchronize_session() is hooked on the init action, so it runs on every HTTP request and processes attacker-controlled ussync-key, ussync-token, and ussync-ref parameters with no nonce, capability, or shared-secret validation. The design relies on AES-256-CBC to protect the token, but the secret key and permitted-domain list are fetched via get_option() keyed on ussync-key; when that slot is unregistered, get_option() returns false, the encryption key falls back to md5('') (a constant, publicly known value) and the domain allowlist becomes an empty string that trivially matches. Combined with a static IV of md5('another-secret'), the entire cryptosystem becomes deterministic and forgeable, so the plugin's own decryption yields an attacker-chosen email and then calls wp_set_auth_cookie() for that user.
RemediationAI
No fixed version is named in the provided data, so treat this as 'No vendor-released patch identified at time of analysis' and verify against the Wordfence advisory (https://www.wordfence.com/threat-intel/vulnerabilities/id/cbc32e6d-47c5-4050-ba77-5a54203fe56a?source=cve) for a release beyond 1.4.0 before relying on an upgrade. Until a patched version is confirmed, the most effective compensating control is to deactivate and remove the User Session Synchronizer plugin, which fully eliminates the init-hooked handler at the cost of losing cross-site session synchronization. If the plugin must remain active, block or filter requests carrying the ussync-key, ussync-token, and ussync-ref parameters at a WAF or reverse proxy (side effect: legitimate synchronization traffic will also be blocked), and restrict access to wp-admin and login flows by IP allowlisting where feasible. Because the flaw grants administrator access, also rotate credentials, invalidate active sessions, and audit for rogue admin accounts after remediation.
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Same weakness CWE-287 – Improper Authentication
View allSame technique Authentication Bypass
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External POC / Exploit Code
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