CVE-2026-56702 in Adminer
Summary
by MITRE • 08/25/2026
Adminer versions before 5.4.3 contain an unrestricted file upload vulnerability in the AdminerFileUpload plugin that allows authenticated users to upload PHP files by exploiting a permissive default extension allowlist. Attackers can upload PHP webshells to columns ending in _path and execute arbitrary code as the web-server user when uploadPath is web-served.
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Analysis
by VulDB Data Team • 08/25/2026
The vulnerability identified in Adminer versions prior to 5.4.3 represents a critical security flaw within the AdminerFileUpload plugin, specifically categorized under CWE-434, which describes an unrestricted file upload that can lead to arbitrary code execution. This issue stems from a permissive default configuration where the system allows files with specific extensions to be uploaded without sufficient validation of their content or context beyond simple extension matching. The core technical flaw lies in the handling of columns ending in _path, which are designed to store file paths rather than binary data. When an authenticated user interacts with these fields, the application accepts uploads based on a whitelist that includes executable script extensions such as PHP. This design oversight fails to distinguish between legitimate static assets and malicious scripts, allowing attackers to bypass standard security controls by simply appending allowed extensions to their payloads.
From an operational perspective, this vulnerability enables remote code execution (RCE) under specific environmental conditions. If the uploadPath configuration is set to a directory that is directly web-served, meaning it is accessible via HTTP requests, any PHP file uploaded through this mechanism becomes immediately executable by the web server process. An attacker who has obtained valid credentials for an account with write access can exploit this flaw to deploy a PHP webshell into the public-facing document root or a subdirectory thereof. Once deployed, the attacker gains full control over the underlying system as the user running the web service, typically resulting in complete compromise of the application server and potential lateral movement within the internal network. This scenario aligns with MITRE ATT&CK technique T1505.003, which involves Server Side Web Shell deployment via file upload mechanisms.
The impact of this vulnerability is severe due to its reliance on authentication rather than being an unauthenticated remote exploit. While this limits the initial attack surface to users who have already compromised or been granted legitimate credentials, it significantly lowers the barrier for exploitation once access is achieved. Attackers often use credential stuffing, phishing, or other initial access vectors to gain entry before leveraging this privilege escalation path via file upload. The ability to execute arbitrary code as the web-server user means that attackers can read sensitive configuration files, exfiltrate database credentials stored in application config files, install backdoors for persistent access, and pivot to other systems connected to the same network segment. In cloud environments or containerized deployments, this could lead to broader infrastructure compromise if the web server has elevated privileges or access to critical services.
Mitigation strategies must address both immediate remediation and long-term architectural improvements. The most effective solution is to upgrade Adminer to version 5.4.3 or later, where the developers have addressed the permissive extension handling in the AdminerFileUpload plugin. For organizations unable to patch immediately due to compatibility constraints, a robust workaround involves modifying the upload configuration to ensure that uploaded files are stored outside of any web-served directory structure. If storage must be within a web-accessible path, it is imperative to configure the web server to deny execution for directories containing user-uploaded content by disabling script interpretation through directives such as php_flag engine off in Apache or location blocks denying execute permissions in Nginx. Additionally, implementing strict Content-Type validation alongside extension checking can provide defense-in-depth, although this should not be relied upon solely due to potential header spoofing risks. Regular auditing of file upload mechanisms and adherence to the principle of least privilege for application accounts further reduces the risk profile associated with such vulnerabilities.