CVE-2026-1916 in WPGSI Plugin
Summary
by MITRE • 02/25/2026
The WPGSI: Spreadsheet Integration plugin for WordPress is vulnerable to unauthorized modification and loss of data due to missing capability checks and an insecure authentication mechanism on the `wpgsi_callBackFuncAccept` and `wpgsi_callBackFuncUpdate` REST API functions in all versions up to, and including, 3.8.3. Both REST endpoints use `permission_callback => '__return_true'`, allowing unauthenticated access. The plugin's custom token-based validation relies on a Base64-encoded JSON object containing the user ID and email address, but is not cryptographically signed. This makes it possible for unauthenticated attackers to forge tokens using publicly enumerable information (admin user ID and email) to create, modify, and delete arbitrary WordPress posts and pages, granted they know the administrator's email address and an active integration ID with remote updates enabled.
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Analysis
by VulDB Data Team • 05/29/2026
The WPGSI Spreadsheet Integration plugin for WordPress presents a critical security vulnerability that undermines the integrity and confidentiality of WordPress installations through improper access control mechanisms and weak authentication implementation. This vulnerability affects all versions up to and including 3.8.3, creating a persistent risk for WordPress users who rely on the plugin for spreadsheet integration functionality. The flaw manifests in two primary REST API endpoints: `wpgsi_callBackFuncAccept` and `wpgsi_callBackFuncUpdate`, which are designed to handle callback functions for spreadsheet data synchronization. These endpoints are exposed without proper authentication requirements, creating an attack surface that allows malicious actors to exploit the system's trust model and gain unauthorized access to critical administrative functions. The vulnerability directly violates fundamental security principles of least privilege and proper authentication, as evidenced by the `permission_callback => '__return_true'` implementation that grants unrestricted access to these endpoints regardless of user authentication status.
The technical implementation of the plugin's authentication mechanism demonstrates a critical design flaw that combines multiple security weaknesses into a single exploitable vector. While the plugin attempts to implement a token-based validation system, this approach fails catastrophically due to the lack of cryptographic signing of the Base64-encoded JSON objects that contain user identifiers and email addresses. The absence of digital signatures means that attackers can easily reconstruct valid tokens by leveraging publicly available information such as administrator user IDs and email addresses that are often discoverable through various reconnaissance techniques. This weakness creates a scenario where an attacker with minimal information can forge authentication tokens and gain access to administrative capabilities that should be restricted to legitimate users only. The vulnerability aligns with CWE-345: Insufficient Verification of Data Authenticity, which specifically addresses the danger of accepting unverified data without proper cryptographic validation, and CWE-287: Improper Authentication, which covers weak authentication mechanisms that can be easily bypassed.
The operational impact of this vulnerability extends far beyond simple unauthorized access, creating a comprehensive threat that can result in complete compromise of WordPress installations and data loss. Attackers can leverage this vulnerability to perform arbitrary modifications to WordPress content, including creating new posts, pages, and media files, as well as deleting existing content and potentially injecting malicious code into the system. The ability to modify content through the REST API endpoints means that attackers can manipulate website content, deface sites, inject malware, or redirect users to malicious destinations. The fact that the vulnerability requires knowledge of the administrator's email address and an active integration ID with remote updates enabled does not adequately protect against determined attackers who can enumerate this information through various means including social engineering, public information discovery, or previous compromise of the system. This vulnerability enables attackers to achieve persistent access and control over WordPress installations, potentially leading to complete site compromise, data exfiltration, and further lateral movement within network environments.
The exploitation of this vulnerability can be achieved through multiple attack vectors that align with the tactics, techniques, and procedures described in the MITRE ATT&CK framework, particularly under the TTPs related to privilege escalation and persistence. The attack begins with reconnaissance to identify active integrations and gather administrator email addresses, followed by exploitation of the unauthenticated REST endpoints using forged tokens. This approach corresponds to ATT&CK technique T1078: Valid Accounts, where attackers leverage legitimate credentials or forged tokens to gain access to systems. The vulnerability also enables techniques such as T1566: Phishing and T1083: File and Directory Discovery, as attackers can use the compromised system to explore the WordPress installation and identify additional targets for exploitation. Organizations should consider implementing network segmentation, monitoring for unusual API access patterns, and conducting regular security assessments to detect and remediate such vulnerabilities before they can be exploited in the wild. The weakness in the plugin's authentication mechanism represents a failure to implement proper cryptographic security measures, which is consistent with the broader class of vulnerabilities that affect web applications and require robust authentication and authorization controls to prevent unauthorized access.
Mitigation strategies for this vulnerability should focus on immediate remediation through plugin updates to versions that address the authentication and authorization flaws, while also implementing additional security controls at the network and application levels. Organizations should ensure that all WordPress installations are regularly updated with the latest security patches, and that plugins are vetted for security vulnerabilities before deployment. The implementation of proper authentication mechanisms including cryptographic signing of tokens, rate limiting on API endpoints, and monitoring for suspicious access patterns can help prevent exploitation of similar vulnerabilities. Security teams should also consider implementing web application firewalls to detect and block malicious API requests, and establish incident response procedures to quickly address potential exploitation attempts. The vulnerability serves as a reminder of the importance of proper security testing and validation of authentication mechanisms in web applications, particularly those that handle sensitive data and administrative functions. Organizations should conduct regular security audits of their WordPress installations and third-party plugins to identify and remediate similar weaknesses that could compromise system integrity and user data.