Sources: National Vulnerability Database, CVE.org, CISA KEV, FIRST EPSS
CVE-2026-76877 Overview
The WPML Multilingual CMS plugin for WordPress is vulnerable to Authentication Bypass via Race Condition in versions up to, and including, 4.9.7. This is due to the `process_iframe_request` function's language-per-domain SSO handler generating the cross-domain sign-in token via `wp_create_nonce('wpml_sso')` on the logout landing page, where the browser has already discarded its authentication cookies — so `wp_get_session_token()` returns an empty string and the token collapses to the shared anonymous nonce for the current 12-hour tick rather than a user-bound secret — and then storing it in the `wpml_sso_user_<token>_<sha256('wpml_sso'.$domain)>` transient mapped to the victim's `user_id` with no binding to the specific sign-out action or requesting client. Because an unauthenticated attacker can independently derive the identical token by triggering the logout confirmation flow on `wp-login.php?action=logout`, and because the `is_iframe_request()` gate conditions (the per-domain SSO `started` transient and domain-hash derived from the public constant `SSO_NONCE`) are fully computable within the 60-second `SSO_TIMEOUT` window, an unauthenticated attacker can submit the forged `wpml_sso_token_domain` parameter with a `wpml_user_signed_in` status to a secondary language-domain endpoint before the legitimate `wpml_user_signed_out` iframe fires, causing WordPress authentication cookies to be issued for the victim. This makes it possible for unauthenticated attackers to gain access to accounts of users — including administrators — who are actively in the process of logging out during the race window.
Critical Impact
Affected Products
- WordPress WPML Multilingual CMS: see the vendor advisory for the exact affected versions
Discovery Timeline
- 2026-11-10: CVE-2026-76877 published to the National Vulnerability Database by security@wordfence.com
- 2026-11-10: last updated in the NVD database
Technical Details for CVE-2026-76877
Vulnerability Analysis
CVE-2026-76877 is a Improper Authentication weakness (CWE-287: Improper Authentication) in WordPress WPML Multilingual CMS. Based on its CVSS vector, the flaw can be reached over the network, needs no login, and needs no user interaction. The software does not properly prove who a user is.
With a CVSS base score of 8.1, apply the vendor fix and confirm exposure on internet facing and business critical assets first.
Root Cause
The weakness is classified as CWE-287: Improper Authentication. The software does not properly prove who a user is.
Attack Vector
Based on the CVSS vector, the flaw can be reached over the network, needs no login, and needs no user interaction. Attack complexity is high complexity.
No exploitation in the wild is confirmed by CISA at the time of the last update. Check the references below for any vendor or researcher proof of concept.
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
Detection Methods for CVE-2026-76877
Detection Strategies
- Inventory every instance of WordPress WPML Multilingual CMS and compare the running version with the affected range above.
- Check external attack surface scans for internet facing instances of the component.
- Run an authenticated vulnerability scan once your scanner ships a check for this CVE.
Monitoring Recommendations
- Forward WordPress WPML Multilingual CMS application, access and audit logs to your SIEM for retrospective hunting.
- Alert on new processes, configuration changes or outbound connections from the affected service.
- Track the vendor advisory and the CISA KEV catalog for changes in exploitation status.
How to Mitigate CVE-2026-76877
Immediate Actions Required
- Apply the fixed version of WordPress WPML Multilingual CMS named in the vendor advisory.
- Prioritize internet facing and business critical instances first.
- Rescan after the change to confirm the exposure is closed.
Patch Information
Use the fixed version listed in the vendor advisory for WordPress WPML Multilingual CMS.
Workarounds
- If patching must wait, restrict network access to the affected service and place it behind authentication or a web application firewall rule.
CWE References
- CWE-287: Improper Authentication More CVEs with this weakness
Technical References
This entry is built directly from NVD, CISA KEV and EPSS data. Verify fixed versions in the vendor advisory before you deploy.
Frequently asked questions
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