CVE-2026-40478
Improper neutralization of specific syntax patterns for unauthorized expressions in Thymeleaf
Description
### 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.
How to fix CVE-2026-40478
To remediate CVE-2026-40478, upgrade the affected package to a fixed version below.
- —upgrade to 3.1.4.RELEASE or later
- —upgrade to 3.1.4.RELEASE or later
- —upgrade to 3.1.4.RELEASE or later
Is CVE-2026-40478 being exploited?
Low — EPSS is 0.1%, meaning exploitation activity has not been observed at scale.
Affected packages (3)
- from 0, < 3.1.4.RELEASE
- from 0, < 3.1.4.RELEASE
- from 0, < 3.1.4.RELEASE
CVSS scores
| Source | Version | Severity | Vector |
|---|---|---|---|
| osv | CVSS 3.1 | CRITICAL9.0 | CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H |