CVE-2026-40478: Improper neutralization of specific syntax patterns for unauthorized expressions in Thymeleaf
Impact A security bypass vulnerability exists in the expression execution mechanisms of Thymeleaf up to and including 3.1.3.RELEASE. 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.
Published Apr 15, 2026 · Updated Apr 24, 2026
Affected packages
org.thymeleaf:thymeleaf
- Ecosystem
- Maven
- Affected
- <= 3.1.3.RELEASE
- Fixed in
- 3.1.4.RELEASE
- Check
mvn dependency:tree -Dincludes=org.thymeleaf:thymeleaf
org.thymeleaf:thymeleaf-spring5
- Ecosystem
- Maven
- Affected
- <= 3.1.3.RELEASE
- Fixed in
- 3.1.4.RELEASE
- Check
mvn dependency:tree -Dincludes=org.thymeleaf:thymeleaf-spring5
org.thymeleaf:thymeleaf-spring6
- Ecosystem
- Maven
- Affected
- <= 3.1.3.RELEASE
- Fixed in
- 3.1.4.RELEASE
- Check
mvn dependency:tree -Dincludes=org.thymeleaf:thymeleaf-spring6
Advisory details
From the GitHub Advisory Database (CC BY 4.0).
Impact
A security bypass vulnerability exists in the expression execution mechanisms of Thymeleaf up to and including 3.1.3.RELEASE. 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).
Patches
This has been fixed in Thymeleaf 3.1.4.RELEASE.
Workarounds
No workaround is available beyond ensuring applications do not pass unvalidated user input directly to the template engine. Upgrading to 3.1.4.RELEASE is strongly recommended in any case.
Credits
Thanks to Dawid Bakaj (VIPentest.com) for responsible disclosure.
References
How this page is made: the data panel comes from the GitHub Advisory Database, CISA’s KEV catalog, the NVD and FIRST EPSS, and updates twice a day. No analysis has been written for this entry yet. Methodology