CVE-2026-111255 in Affiliate Toolkit Plugin
Summary
by MITRE • 10/28/2026
The affiliate-toolkit – Multi-Network Affiliate & Amazon Product Display plugin for WordPress is vulnerable to Arbitrary File Upload in all versions up to, and including, 3.9.2 via the upload_image function. This is due to insufficient file type validation in upload_image due to a weak Content-Type prefix check and extension derivation from the attacker-controlled URL path, with no dangerous-extension stripping. This makes it possible for authenticated attackers, with contributor-level access and above, to upload files that may be executable, which makes remote code execution possible. Exploitation requires the "import product image" option to be enabled in the plugin settings, as this activates the image download pipeline triggered on product post save.
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Analysis
by VulDB Data Team • 10/28/2026
The affiliate-toolkit – Multi-Network Affiliate & Amazon Product Display plugin for WordPress contains a critical security vulnerability affecting all versions up through 3.9.2 that allows authenticated attackers to achieve remote code execution via arbitrary file upload. This flaw is located within the upload_image function, which serves as an entry point for processing image uploads during product post saves when the import product image option is enabled in the plugin settings. The core technical deficiency lies in insufficient validation of uploaded files, specifically regarding how the system determines whether a file is safe to store on the server. Instead of performing robust content-type verification or analyzing the actual binary signature of the file, the vulnerability stems from a weak Content-Type prefix check and an insecure method for deriving the file extension directly from the attacker-controlled URL path provided in the request payload.
This architectural weakness means that if an attacker provides a URL pointing to a malicious script with a deceptive filename ending in .php or another executable extension, the plugin will accept it without stripping dangerous extensions or verifying that the underlying data actually matches the claimed image format. Because there is no mechanism to validate the file content against its declared type, attackers can bypass standard security controls by simply manipulating the URL path to include an allowed but dangerous extension while ensuring the Content-Type header suggests a benign media type such as image/jpeg or image/png. This combination of flawed validation logic allows malicious PHP code or other server-side executable scripts to be written directly into the WordPress upload directory, where they can subsequently be executed by the web server.
The operational impact of this vulnerability is severe, resulting in full remote code execution on the compromised WordPress instance. Since exploitation requires authenticated access with at least contributor-level privileges, it targets users who have been granted limited administrative rights but still possess sufficient trust to manage content and media assets. Once an attacker successfully uploads a web shell through this vector, they gain the ability to execute arbitrary commands within the context of the web server process. This typically leads to complete compromise of the underlying operating system, unauthorized access to sensitive databases, installation of persistent backdoors, and potential lateral movement across the network infrastructure hosting the WordPress application. The requirement for specific plugin settings to be enabled means that while not every instance is immediately vulnerable by default, any site with this feature activated remains at high risk if user accounts are compromised or if privilege escalation occurs within the platform.
From a classification perspective, this vulnerability aligns with CWE-434, which describes the unrestricted upload of files with dangerous types, and CWE-20, indicating improper input validation where external data is not sufficiently verified before use in security decisions. In terms of offensive cyber operations mapping, this exploit technique corresponds to ATT&CK T1505.003, specifically Server Side Request Forgery leading to file upload, or more broadly T1105 for Ingress Tool Transfer when the uploaded script facilitates further malicious activity. The lack of extension stripping and reliance on URL-derived metadata represents a classic implementation error where developers assume that client-supplied headers are trustworthy without cross-referencing them against actual file signatures.
Mitigation strategies must address both immediate remediation and long-term defensive posture improvements. The most effective solution is to upgrade the affiliate-toolkit plugin to version 3.9.3 or later, where these validation checks have been corrected to enforce strict allow-listing of permitted image extensions and perform deep content inspection rather than relying on superficial header analysis. For environments unable to patch immediately due to compatibility constraints, administrators should disable the import product image feature within the plugin settings if it is not actively required for business operations, thereby removing the attack surface entirely. Additionally, implementing web application firewall rules that detect anomalous file upload patterns and restricting write permissions on WordPress directories can provide an additional layer of defense against exploitation attempts by preventing successful execution even if a malicious file is uploaded.