thymeleaf/thymeleaf-spring5/thymeleaf-spring6 up to 3.1.3 expression language injection

Summaryinfo

A vulnerability marked as problematic has been reported in thymeleaf, thymeleaf-spring5 and thymeleaf-spring6 up to 3.1.3. Affected is an unknown function. This manipulation causes expression language injection. The identification of this vulnerability is CVE-2026-40478. It is possible to initiate the attack remotely. There is no exploit available. It is suggested to upgrade the affected component.

Detailsinfo

A vulnerability has been found in thymeleaf, thymeleaf-spring5 and thymeleaf-spring6 up to 3.1.3 and classified as problematic. Affected by this vulnerability is an unknown code. The manipulation with an unknown input leads to a expression language injection vulnerability. The CWE definition for the vulnerability is CWE-917. The product constructs all or part of an expression language (EL) statement in a framework such as a Java Server Page (JSP) using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify the intended EL statement before it is executed. As an impact it is known to affect confidentiality, integrity, and availability. The summary by CVE is:

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.

It is possible to read the advisory at github.com. This vulnerability is known as CVE-2026-40478 since 04/13/2026. The exploitation appears to be difficult. The attack can be launched remotely. The exploitation doesn't need any form of authentication. The technical details are unknown and an exploit is not publicly available.

Upgrading to version 3.1.4 eliminates this vulnerability.

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Productinfo

Name

• thymeleaf
• thymeleaf-spring5
• thymeleaf-spring6

Version

• 3.1.0
• 3.1.1
• 3.1.2
• 3.1.3

Website

• Product: https://github.com/thymeleaf/thymeleaf/

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