CVE-2026-40478: Improper neutralization of specific syntax patterns for unauthorized expres

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.

Affected products

Version statuses are supplied by the assigning organization. Consult the original record for detailed ranges and platform conditions.

thymeleaf thymeleaf

< 3.1.4.RELEASEaffected

thymeleaf org.thymeleaf:thymeleaf-spring5

< 3.1.4.RELEASEaffected

thymeleaf org.thymeleaf:thymeleaf-spring6

< 3.1.4.RELEASEaffected

CVE-2026-40478

Improper neutralization of specific syntax patterns for unauthorized expressions in Thymeleaf