CRITICAL: CVE-2026-40477 (CVSS 9) — thymeleaf thymeleaf

CVE: CVE-2026-40477

CVSS: 9 (3.1) — CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H

Severity: CRITICAL

Status: Critical advisory

Affected

thymeleaf thymeleaf

Summary

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 expression execution mechanisms. Although the library provides mechanisms to prevent expression injection, it fails to properly restrict the scope of accessible objects, allowing specific potentially sensitive objects to be reached from within a template. 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.

Verified Sources

References

https://github.com/thymeleaf/thymeleaf/security/advisories/GHSA-r4v4-5mwr-2fwr

_Validated by the Lyrie Threat Intelligence Pipeline — 3 independent sources confirmed before publication. No speculation._

Lyrie Verdict

A vulnerability of this severity is exactly what Lyrie's anti-rogue-AI defense is built for: continuous, autonomous monitoring that doesn't wait for human reaction time.

#thymeleaf #critical