CVE-2026-18781 in Drag and Drop Multiple File Upload for Contact Form 7 Plugin
Summary
by MITRE • 08/21/2026
The Drag and Drop Multiple File Upload for Contact Form 7 WordPress plugin before 1.3.9.9 does not validate the final name of an uploaded file after stripping characters from it, allowing unauthenticated users to defeat its file type restrictions and execute arbitrary code on the server.
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Analysis
by VulDB Data Team • 08/21/2026
The vulnerability identified in versions of the Contact Form 7 WordPress plugin prior to version 1.3.9.9 represents a critical security flaw within the drag-and-drop multiple file upload functionality. This issue stems from an insufficient validation mechanism that fails to properly sanitize and verify filenames after initial character stripping operations are performed. The core technical failure lies in the sequence of operations where the application processes user-supplied input for filename sanitization but does not re-validate the resulting string against security policies before accepting it as a valid file path or name. This oversight allows attackers to manipulate the final resolved filename, effectively bypassing the intended restrictions on allowed file types and extensions.
From an operational perspective, this flaw enables unauthenticated remote code execution with significant severity. An attacker can craft a malicious payload disguised within a seemingly benign upload request by exploiting the gap between the initial character stripping logic and the final acceptance of the file name. By carefully constructing filenames that survive the sanitization process while retaining executable extensions or dangerous characters, an adversary can trick the server into storing web shell scripts in accessible directories. Once these files are uploaded, they can be invoked via HTTP requests to execute arbitrary commands on the underlying system, leading to a complete compromise of the WordPress installation and potentially the host environment.
This vulnerability aligns with CWE-434, which describes the unrestricted upload of file with dangerous type, as well as CWE-20, indicating improper input validation where external data is not adequately verified before use in security-critical decisions. In terms of attack vectors, this flaw facilitates exploitation consistent with MITRE ATT&CK techniques related to Initial Access through web applications and Execution via command line scripts uploaded to the server. The lack of strict enforcement on final file names after transformation creates a classic path traversal or arbitrary write scenario that undermines the integrity of the application's security controls.
Mitigation for this vulnerability requires an immediate upgrade to version 1.3.9.9 or later, where the developers have implemented stricter validation protocols for uploaded filenames. Administrators should ensure that their WordPress environments are updated promptly to close this attack vector. Additionally, defense-in-depth strategies such as configuring web servers to prevent execution of scripts in upload directories and implementing strict Content Security Policies can provide additional layers of protection against similar exploitation attempts even if other vulnerabilities exist within the application stack.