RCE in Thymeleaf Org.thymeleaf:thymeleaf-Spring5

CVE-2026-40478

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.

Vulnerability class: Log4Shell (CVE-2021-44228)

Published · last modified .

CVSS v3 metric

CVSS v3 base score 9.0 (Critical). Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H.

EPSS exploit prediction

EPSS: 0.012 (67.1th percentile), scored .

Low probability of exploitation in the next 30 days, but still tracked. 67th percentile — 67.1% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS trend (30 days)EPSS over the last 30 days for CVE-2026-40478: held from 0.009 to 0.012.

EPSS over last 30 days · oldest: 0.009 · newest: 0.012 · change: +0.003

Affected products

Weakness classification (CWE)

References

Frequently asked questions

What is CVE-2026-40478?
CVE-2026-40478 is a critical-severity vulnerability in Thymeleaf Org.thymeleaf:thymeleaf-Spring5, classified under Improper Neutralization of Special Elements used in an Expression Language Statement (Expression Language Injection). CVSS score: 9.0/10. Published 2026-04-17.
How severe is CVE-2026-40478?
Critical severity. CVSS v3 base score is 9.0 out of 10.