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CVE-2026-40478

Thymeleaf code injection

9.0 CRITICALEPSS 1.20%
  1. Published17 Apr 2026

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.

CVSS 3.1 breakdown

Attack vectorNetwork
Attack complexityHigh
Privileges requiredNone
User interactionNone
ScopeChanged
ConfidentialityHigh
IntegrityHigh
AvailabilityHigh
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H

Affected products

Thymeleaf< 3.1.4

Remediation

Fixed in
Thymeleaf≥ 3.1.4

References

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Frequently asked

Is CVE-2026-40478 being actively exploited?

CVE-2026-40478 is not in the CISA KEV catalog. Its EPSS exploit probability is 1.20%.

How severe is CVE-2026-40478?

CVE-2026-40478 has a CVSS 3.1 base score of 9.0, rated critical. EPSS estimates a 1.20% probability of exploitation.

Which products are affected by CVE-2026-40478?

Affected products include Thymeleaf.

How do I fix CVE-2026-40478?

Upgrade affected software to a fixed version, for example Thymeleaf 3.1.4 or later, then confirm no affected versions remain in your inventory.

How Secuno handles this

Secuno correlates vulnerabilities like CVE-2026-40478 against the real software inventory on every managed device, as each hourly inventory arrives. Rather than a static severity, each match is scored in context: exploit availability, EPSS, the asset's exposure, and business criticality decide where it lands in the queue. If an affected version is present anywhere across your portfolio, it surfaces automatically with a prioritised remediation path.

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Data from the NVD, CISA KEV catalog and FIRST EPSS. CVSS 3.1 base score shown where available.