CVE-2026-40478
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedThymeleaf 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.
In the news
Third-party coverageSurfaced from public web coverage — external links open in a new tab.
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysis · high confidenceThymeleaf versions 3.1.3 and prior contain a security bypass in expression execution mechanisms that allows Server-Side Template Injection (SSTI). Although Thymeleaf provides protections against expression injection, it fails to properly neutralize specific syntax patterns. When developers pass unvalidated user input directly to the template engine, attackers can bypass these protections to achieve remote code execution.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.
NVD · CPE data< 3.1.4CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Network
- Complexity
- High
- Privileges
- None
- User interaction
- None
- Scope
- Changed
- Confidentiality
- High
- Integrity
- High
- Availability
- High
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H
Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.
dbcve checksWork through these to decide whether this CVE applies to you.
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Identify Thymeleaf versionCheck your project's dependency management file (pom.xml for Maven or build.gradle for Gradle) for the thymeleaf library version, or run a dependency command to list the installed Thymeleaf versionAffected if The version is 3.1.3 or prior (any version below 3.1.4)
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Inspect template processing codeReview source code where user-supplied input (request parameters, headers, body content) is passed directly to Thymeleaf template processing methods such as setVariable, process, or template engine execution callsAffected if User input is directly concatenated or passed into template engine methods without validation or sanitization
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Review template files for direct input usageExamine Thymeleaf templates (HTML, XML, TXT files in src/main/resources/templates) for patterns where request parameters or model attributes containing user data are used in expression syntax (${...}, *{...}, #{...})Affected if Templates contain expressions that directly reference user-controlled parameters without validation wrappers
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Audit template engine configurationCheck the Thymeleaf TemplateEngine configuration in your application code for whether sandbox mode is enabled or if expression protection mechanisms are in placeAffected if No sandboxing or additional expression protection is configured and user input flows to templates
You are affected if your Thymeleaf version is below 3.1.4 AND user-provided input is directly passed to the template engine without validation or sandboxing.
Generated from the published advisory. Verify against your own configuration.
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
dbcve · scoped3.1.4
Upgrade to Thymeleaf 3.1.4.RELEASE or later, and ensure no unvalidated user input is passed directly to the template engine—implement proper input validation as a defense-in-depth measure.
3.1.4.RELEASE
- Identify the build tool used in the project (Maven pom.xml or Gradle build.gradle)
- Locate the Thymeleaf dependency declaration
- Update the Thymeleaf version from the current version to 3.1.4.RELEASE
- For Maven: Change version in pom.xml to org.thymeleaf:thymeleaf:3.1.4.RELEASE
- For Gradle: Change dependency to implementation 'org.thymeleaf:thymeleaf:3.1.4.RELEASE'
- Rebuild the project to download the new version
- Test the application to ensure functionality remains intact after the upgrade
Generated from the published advisory — verify against the referenced sources before acting.
- Consultation4.0 h
- Implementation8.0 h
- Testing6.0 h
- Review / QA4.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2026-40478 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2026-40478 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- Verified mitigations, workarounds, and config changes
- Version or environment caveats, and links to real fixes
- No weaponised exploit code, or anything meant to cause harm
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