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CVE-2026-40478

9.0 · CRITICAL

Thymeleaf is a server-side Java template engine for web and standalone environments.

Published Apr 17, 2026CWE-917EPSS 1.20%

Overview

CVE-2026-40478 is a critical-severity vulnerability. It was published on April 17, 2026 and has a CVSS 3.1 base score of 9.0 (CRITICAL).

This vulnerability has a CVSS 3.1 base score of 9.0, rated CRITICAL. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.

Technical 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.

Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

References

GitHubgithub.com/thymeleaf/thymeleaf/security/advisories/GHSA-xjw8-8c5c-9r79Refaccess.redhat.com/errata/RHSA-2026:21772Refaccess.redhat.com/security/cve/CVE-2026-40478Refbugzilla.redhat.com/show_bug.cgi?id=2459349Refsecurity.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-40478.json

How CyberStrike helps

Frequently asked questions

What is CVE-2026-40478?

CVE-2026-40478 is a critical-severity vulnerability. It was published on April 17, 2026 and has a CVSS 3.1 base score of 9.0 (CRITICAL).

How severe is CVE-2026-40478?

This vulnerability has a CVSS 3.1 base score of 9.0, rated CRITICAL. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.

How do I fix or remediate CVE-2026-40478?

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

How can CyberStrike help with CVE-2026-40478?

CyberStrike is an open-source, AI-augmented pentesting engine. Rather than flag a version number, it tests whether an issue like CVE-2026-40478 is actually reachable in your own applications and APIs, then verifies each finding before reporting it. That tells you if the weakness is a real, exploitable risk in your environment or a false positive you can safely deprioritize.

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