CVE-2026-40478 Thymeleaf Template Injection: From Sandbox Bypass to Unauthenticated RCE
CVE-2026-40478 Thymeleaf Template Injection: From Sandbox Bypass to Unauthenticated RCE Overview Published: 04/17/2026 CVE-ID: CVE-2026-40478 CVSS: 9.1 Critical Affected Engine: Thymeleaf Server Side Template Engine Affected Versions: 3.1.3.RELEASE and prior CWE: CWE-917: Improper Neutralization of Special Elements used in an Expression Language Statement (‘Expression Language Injection’) and CWE-1336: Improper Neutralization of Special Elements Used in a Template Engine Description Thymeleaf is a server-side Java template engine for web and standalone environments. Versions 3.1.3.RELEASE and prior contain a security bypass vulnerability in the the expression execution mechanisms. Although the library provides mechanisms to prevent expression injection, it fails to properly neutralize specific syntax patterns that allow for the execution of unauthorized expressions. If an application developer passes unvalidated user input directly to the template engine, an unauthenticated remote attacker can bypass the library’s protections to achieve Server-Side Template Injection (SSTI). This issue has ben fixed in version 3.1.4.RELEASE. ...