What’s Vulnerable › Vulnerabilities

CVE-2026-40478: Improper neutralization of specific syntax patterns for unauthorized expressions in Thymeleaf

• Severity: critical (CVSS 9.0 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 1.1% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-04-17 · updated 2026-10-26
• Weakness: CWE-917

Description

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 products

• thymeleaf: before 3.1.4 — fixed in 3.1.4

How to fix

Upgrade to a fixed version: thymeleaf 3.1.4. Check the vendor advisory for mitigations.

References

• https://github.com/thymeleaf/thymeleaf/security/advisories/GHSA-xjw8-8c5c-9r79
• https://access.redhat.com/errata/RHSA-2026:21772
• https://access.redhat.com/security/cve/CVE-2026-40478
• https://bugzilla.redhat.com/show_bug.cgi?id=2459349
• https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-40478.json

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