CVE-2026-40478
CRITICALDescription
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.
How to fix
TridentStack Control can deploy fixes like this automatically across your Windows, macOS, and Linux fleet. See how it works
Remediation is compiled from vendor and distribution security advisories. Always confirm against the linked source for your exact version and platform.
CVSS v3 Vector
Exploitability
Impact
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H
Exploit Intelligence
Moderate risk: more likely to be exploited than 67% of all known CVEs.
References
Related Vulnerabilities
Other CWE-917 vulnerabilities, ordered by exploit likelihood. View all
| CVE | Severity | CVSS | EPSS | Exploited | Fix |
|---|---|---|---|---|---|
| CVE-2022-26134 | Critical | 9.8 | 100% | KEV + Ransom | Fix |
| CVE-2021-44228 | Critical | 10.0 | 100% | KEV + Ransom | Fix |
| CVE-2021-26084 | Critical | 9.8 | 100% | KEV + Ransom | Fix |
| CVE-2021-45046 | Critical | 9.0 | 100% | KEV + Ransom | Fix |
| CVE-2022-22963 | Critical | 9.8 | 100% | KEV | - |
| CVE-2020-10199 | High | 8.8 | 99% | KEV | Fix |
Common questions
How do I fix CVE-2026-40478?
Upgrade thymeleaf to 3.1.4 or later.
Is CVE-2026-40478 being actively exploited?
Not that we know of. CVE-2026-40478 is not in the CISA Known Exploited Vulnerabilities catalog. Its EPSS score of 1.2% is the estimated probability that it will be exploited in the next 30 days. That is higher than 67% of all scored CVEs.
How severe is CVE-2026-40478?
CVE-2026-40478 has a CVSS v3 base score of 9.0, rated critical. CVSS rates the technical impact if the vulnerability is exploited, not how likely that is, so weigh it alongside the exploit-prediction score when you decide what to patch first.
What does CVE-2026-40478 affect?
Published advisories record a fix for thymeleaf (NVD). Only products with a sourced advisory are listed, so treat this as what we can cite rather than a complete inventory.
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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2026-08-18.