CVE-2026-39793 in Simple JWT Login Plugin
Summary
by MITRE • 10/06/2026
Subscriber Broken Authentication in Simple JWT Login 4.0.0 versions.
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Analysis
by VulDB Data Team • 10/06/2026
The vulnerability identified as Subscriber Broken Authentication in Simple JWT Login version 4.0.0 represents a critical flaw within the authentication mechanism of this widely used WordPress plugin, which facilitates JSON Web Token based user sessions. This issue stems from an improper implementation or validation logic that allows attackers to bypass standard authentication checks, effectively granting unauthorized access to subscriber-level accounts and potentially higher privileged roles depending on the specific configuration and exploitation vector employed. The core technical flaw involves a failure in verifying the integrity or origin of JWT tokens during the login process, which contradicts fundamental security principles regarding identity verification and session management.
From a technical perspective, this vulnerability aligns with CWE-287 Improper Authentication, where the system fails to correctly verify that an entity is who it claims to be before granting access to resources. In the context of JWT-based systems, such flaws often arise from weak secret key handling, lack of signature verification on specific endpoints, or logic errors in token expiration and audience validation checks. An attacker can exploit this by crafting malicious tokens or manipulating request parameters that bypass the intended authentication flow, thereby establishing a valid session without possessing legitimate credentials. This type of error is particularly dangerous because it undermines the trust model upon which stateless API architectures rely, allowing for unauthorized data access and potential privilege escalation if the compromised account holds administrative rights.
The operational impact of this vulnerability extends beyond simple unauthorized login, as it can lead to significant data breaches within WordPress environments that utilize JWTs for headless CMS setups or mobile application backends. Attackers leveraging this flaw can perform actions on behalf of legitimate users, including modifying content, accessing private user data, and potentially escalating privileges if the authentication bypass affects higher-level roles such as administrators. This compromises the confidentiality, integrity, and availability of the affected system, eroding trust in the platform's security posture and exposing sensitive information to malicious actors who can exploit these unauthorized sessions for further attacks or financial gain through defacement or malware distribution.
To mitigate this risk, immediate action is required by updating Simple JWT Login to a patched version that addresses the authentication validation logic flaws. Administrators should also enforce strong password policies and consider implementing multi-factor authentication where possible to add an additional layer of security beyond token-based access. Regular auditing of plugin configurations and ensuring that secret keys are sufficiently complex and rotated periodically can further reduce the attack surface. Monitoring logs for anomalous login patterns, such as repeated failed attempts followed by successful authentications from unusual IP addresses or user agents, can help in early detection of exploitation attempts while waiting for official patches to be deployed across all affected instances.
This vulnerability is also relevant to MITRE ATT&CK techniques related to Initial Access and Credential Access, specifically those involving valid accounts obtained through authentication bypasses. Security teams should review their access control lists and session management policies to ensure that no single point of failure exists within the JWT validation pipeline. By addressing these weaknesses, organizations can restore confidence in their authentication mechanisms and prevent unauthorized entities from leveraging broken logic to infiltrate protected systems and exfiltrate sensitive data.