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Sandboxed Thymeleaf expressions vulnerable to improper recognition of unauthorized syntax patterns

Critical severity GitHub Reviewed Published Apr 29, 2026 in thymeleaf/thymeleaf • Updated May 4, 2026

Package

maven org.thymeleaf:thymeleaf (Maven)

Affected versions

<= 3.1.4.RELEASE

Patched versions

3.1.5.RELEASE
maven org.thymeleaf:thymeleaf-spring5 (Maven)
<= 3.1.4.RELEASE
3.1.5.RELEASE
maven org.thymeleaf:thymeleaf-spring6 (Maven)
<= 3.1.4.RELEASE
3.1.5.RELEASE

Description

Impact

A security bypass vulnerability exists in the expression execution mechanisms of Thymeleaf up to and including 3.1.4.RELEASE. Although the library provides mechanisms to avoid the execution of potentially dangerous expressions in some specific sandboxed (restricted) contexts, it fails to properly neutralize specific constructs that allow this kind of expressions to be executed. If an application developer passes to the template engine unsanitized variables that contain such expressions, and these values are used in sandboxed contexts inside the templates, these expressions can be executed achieving Server-Side Template Injection (SSTI).

Patches

This has been fixed in Thymeleaf 3.1.5.RELEASE. All users are advised to upgrade immediately.

Workarounds

No workaround is available beyond ensuring applications do not pass unvalidated/unsanitized data directly to the template engine. Upgrading to 3.1.5.RELEASE is strongly recommended in any case.

References

@danielfernandez danielfernandez published to thymeleaf/thymeleaf Apr 29, 2026
Published to the GitHub Advisory Database May 4, 2026
Reviewed May 4, 2026
Last updated May 4, 2026

Severity

Critical

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Network
Attack complexity
High
Privileges required
None
User interaction
None
Scope
Changed
Confidentiality
High
Integrity
High
Availability
High

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H

EPSS score

Weaknesses

Improper Neutralization of Special Elements used in an Expression Language Statement ('Expression Language Injection')

The product constructs all or part of an expression language (EL) statement in a framework such as a Java Server Page (JSP) using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify the intended EL statement before it is executed. Learn more on MITRE.

Improper Neutralization of Special Elements Used in a Template Engine

The product uses a template engine to insert or process externally-influenced input, but it does not neutralize or incorrectly neutralizes special elements or syntax that can be interpreted as template expressions or other code directives when processed by the engine. Learn more on MITRE.

CVE ID

CVE-2026-41901

GHSA ID

GHSA-c9ph-gxww-7744

Source code

Credits

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