CVE-2026-40478: Thymeleaf is a server-side Java template engine for web and standalone environments

Q: How do I fix CVE-2026-40478?

thymeleaf: upgrade to 3.1.4. Exact commands for each OS are on this page.

Q: Is CVE-2026-40478 being exploited?

CVE-2026-40478 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2026-40478 affect?

CVE-2026-40478 affects thymeleaf. Severity is critical (CVSS 9.0). 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 mechanis

Q: How urgent is CVE-2026-40478?

Priority 53/100. Critical severity; Remotely exploitable, no login, no user action

This month

CRITICAL 9.0REMOTEUPGRADE

CVE-2026-40478 is a critical-severity flaw (CVSS 9.0) affecting thymeleaf. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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 d

Why this priority

Critical severity
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	9.0 (Critical)
Attack vector	Network (remote)
Attack complexity	High
Privileges needed	None
User interaction	None
EPSS exploit chance	1.1% (top 35%)
CISA exploited list	No
Weakness	CWE-917, CWE-1336
Published	2026-04-17
Last modified	2026-10-26

Publisher (CNA): GitHub, Inc. · Vendor: thymeleaf

Last updated 2026-10-26 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-04-17 22:16 UTCPublished CVE record published
2026-10-26 21:10 UTCUpdated Record last modified

thymeleaf thymeleaf UPGRADE

Affected: < 3.1.4

Fixed in: 3.1.4

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy thymeleaf || rpm -q thymeleaf || thymeleaf --version

2. UPGRADE to 3.1.4 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade thymeleaf

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade thymeleaf

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

Advisories and coverage

Research and news

Snyk Security: Don't Panic: The Thymeleaf Template Injection That Only Hurts If You Let It (CVE-2026-40478) 2026-04-29

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-40478?

thymeleaf: upgrade to 3.1.4. Exact commands for each OS are on this page.

Is CVE-2026-40478 being exploited?

CVE-2026-40478 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-40478 affect?

CVE-2026-40478 affects thymeleaf. Severity is critical (CVSS 9.0). 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 mechanis

How urgent is CVE-2026-40478?

Priority 53/100. Critical severity; Remotely exploitable, no login, no user action

Software pages

Java vulnerabilities

Related CVEs

CVE-2026-40477 CRITICAL 9.0 UPGRADE Thymeleaf is a server-side Java template engine for web and standalone environments

References

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