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CVE-2026-41901 is a server-side template injection vulnerability in Thymeleaf versions before 3.1.5.RELEASE. Thymeleaf's restricted expression-execution contexts are intended to prevent dangerous expression evaluation, but specific constructs are not properly neutralized and can bypass those restrictions. When an application supplies unsanitized variable values containing attacker-controlled expressions and uses them in these sandboxed template contexts, Thymeleaf can evaluate the expressions.
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1 valid exploit after Mallory filtered fakes, detection scripts, and README-only repos (1 hidden).
This repository is a small standalone Bash-based proof-of-concept exploit plus a local lab builder. It contains two executable scripts: setup-lab.sh creates a vulnerable Spring Boot/Thymeleaf application inside Docker, and exploit-cve-2026-41901.sh sends crafted Thymeleaf expression payloads to that app to demonstrate remote command execution. Repository structure and purpose: - README.md: usage notes and references. - exploit-cve-2026-41901.sh: main exploit script. - setup-lab.sh: generates a full local test lab, including pom.xml, Java controller, Thymeleaf template, and Dockerfile. Main exploit behavior: - Targets http://localhost:8080/poc. - Uses curl with a GET parameter named input. - Injects a Thymeleaf expression of the form [[${...}]]. - The expression calls T(java.lang.Runtime).getRuntime().exec("<cmd>") and reads stdout with java.util.Scanner. - Iterates through several hardcoded commands: id, whoami, hostname, ls /tmp, and cat /etc/passwd | head -5. - Greps the HTTP response for indicative output strings, implying the exploit expects reflected command output rather than a purely blind channel. Lab setup behavior: - Builds a Maven-based Spring Boot 3.2.0 application with Thymeleaf 3.1.4.RELEASE. - Exposes a GET /poc endpoint that accepts input and stores it in the model as userInput. - Generates a Thymeleaf template that reflects userInput and also includes a hardcoded Runtime.exec('whoami') demonstration in a <pre> block. - Builds and runs the app in Docker, publishing port 8080 to localhost. Assessment: - This is a real exploit POC, not merely a detector. - It is operational because it includes a working payload and a reproducible vulnerable lab, but it is not highly weaponized: commands and target are hardcoded and there is no generalized payload customization, stealth, or post-exploitation automation. - The attack vector is web/network-based expression injection leading to server-side command execution.
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