CVE-2026-40478

Improper neutralization of specific syntax patterns for unauthorized expressions in Thymeleaf

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.

Affected

thymeleaf · org.thymeleaf:thymeleaf-spring5 · org.thymeleaf:thymeleaf-spring6

CVSS v3.1 CNA

8.5 HIGHCVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:H

CVSS v3.1 GITHUB

9.0 CRITICALCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H

EPSS

1.20% chance of exploitation in the next 30 days, 68th percentile

Published

2026-04-17

Updated

2026-08-18

Proof-of-concept exploits (1)

• bmvermeer/thymeleaf.CVE_2026_404781★ · 2026-04-29

Security advisories

• thymeleaf/thymeleaf/security/advisories/GHSA-xjw8-8c5c-9r79
• advisories/GHSA-xjw8-8c5c-9r79

References

• CVE Record
• NVD entry