TinyWeb is a lightweight web server written in Delphi for Win32 platforms. Versions prior to 2.01 contain a critical vulnerability (CVE-2026-27613) classified as CWE-78 (OS Command Injection) and CWE-88 (Argument Injection or Modification). This vulnerability arises from improper neutralization of special elements in CGI parameters, allowing unauthenticated remote attackers to bypass CGI parameter security controls. Attackers can exploit this flaw by crafting malicious requests that inject OS commands through CGI parameters, particularly targeting CGI executables that accept command-line flags, such as php-cgi.exe. The impact varies by configuration: it can lead to source code disclosure or full remote code execution (RCE). The vulnerability does not require authentication or user interaction, making it highly exploitable. The vendor patched the issue in TinyWeb version 2.01. If immediate upgrading is not feasible, enabling the STRICT_CGI_PARAMS directive (enabled by default in define.inc) can mitigate the risk by enforcing stricter parameter validation. Additionally, avoiding CGI executables that accept dangerous flags reduces exposure. Deploying a Web Application Firewall (WAF) to block URL query parameters starting with a hyphen or containing encoded double quotes (%22) can further protect vulnerable servers. The CVSS 4.0 score of 10.0 reflects the critical nature of this vulnerability, with network attack vector, no required privileges or user interaction, and high impact on confidentiality, integrity, and availability.

The vulnerability poses a critical risk to organizations running TinyWeb versions prior to 2.01, especially those hosting CGI scripts like PHP. Successful exploitation can lead to unauthorized disclosure of sensitive source code, exposing intellectual property and potentially credentials or configuration data. More severely, attackers can achieve remote code execution, allowing full system compromise, data theft, lateral movement, or deployment of malware such as ransomware. Since no authentication or user interaction is required, the attack surface is broad and easily exploitable remotely over the network. This can disrupt business operations, cause data breaches, and damage organizational reputation. Environments with public-facing TinyWeb servers are at highest risk. The vulnerability also threatens hosting providers and managed service providers using TinyWeb, potentially impacting multiple clients. The critical severity and ease of exploitation make this a high-priority issue for incident response and patch management teams worldwide.

1. Upgrade TinyWeb to version 2.01 or later immediately to apply the official patch. 2. If upgrading is not immediately possible, ensure the STRICT_CGI_PARAMS directive is enabled in define.inc to enforce strict CGI parameter validation. 3. Avoid using CGI executables that accept dangerous command-line flags, such as php-cgi.exe, on vulnerable TinyWeb versions. 4. Deploy a Web Application Firewall (WAF) configured to block URL query parameters that start with a hyphen (-) or contain encoded double quotes (%22), as these are indicators of exploitation attempts. 5. Restrict network access to TinyWeb servers by implementing IP whitelisting or VPN access where feasible to reduce exposure. 6. Monitor web server logs for suspicious requests containing unusual CGI parameters or command injection patterns. 7. Conduct regular security assessments and penetration tests focusing on CGI interfaces. 8. Educate system administrators about the risks of running outdated TinyWeb versions and the importance of patching and secure CGI configurations.