---
id: CVE-2026-40478
title: >-
  Thymeleaf is a server-side Java template engine for web and standalone
  environments
summary: >-
  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 mecha…
severity: critical
cvss: 9
cvssVector: 'CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H'
cwe:
  - CWE-917
  - CWE-1336
  - CWE-917
vendor: thymeleaf
product: thymeleaf
affected:
  - thymeleaf < 3.1.4
patched:
  - thymeleaf 3.1.4
published: '2026-04-17'
updated: '2026-08-04'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-40478'
references:
  - url: >-
      https://github.com/thymeleaf/thymeleaf/security/advisories/GHSA-xjw8-8c5c-9r79
    label: security-advisories@github.com
  - url: 'https://access.redhat.com/errata/RHSA-2026:21772'
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
  - url: 'https://access.redhat.com/security/cve/CVE-2026-40478'
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
  - url: 'https://bugzilla.redhat.com/show_bug.cgi?id=2459349'
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
  - url: >-
      https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-40478.json
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
tags:
  - nvd
epss: 0.01102
epssPercentile: 0.64296
ingestedAt: '2026-08-05T12:47:47.769Z'
---

## Overview

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

- `thymeleaf < 3.1.4`

## Remediation

Upgrade past the affected range:

- `thymeleaf 3.1.4`