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Full vulnerability report · 2026
CVE-2026-40478High confidence

Improper neutralization of specific syntax patterns for unauthorized expressions in Thymeleaf

thymeleaf · thymeleaf

9.1CriticalCVSS 3.1
Recommended action
Within 72 hours

Critical technical impact with a remotely reachable, unauthenticated path; no CISA KEV confirmation is currently recorded.

Patch available
Direct vendor intelligence

Authoritative vendor CSAF and VEX advisories

Structured product status and remediation from the issuing vendor. Product-state explanations are always visible; large lists can be searched or downloaded.

1 current
CVE-2026-40478 · CSAF 2.0 · revision 3 · finalRed Hat Product Securitythymeleaf: Thymeleaf: Server-Side Template Injection via expression execution bypass
5 known affected

The vendor explicitly identifies these products as affected by this CVE.

  • thymeleaf as a component of Red Hat Fuse 7
  • spring-boot-starter-thymeleaf as a component of Red Hat Single Sign-On 7
  • thymeleaf as a component of Red Hat Single Sign-On 7
  • thymeleaf-extras-java8time as a component of Red Hat Single Sign-On 7
  • thymeleaf-spring5 as a component of Red Hat Single Sign-On 7
Summary
A flaw was found in Thymeleaf, a server-side Java template engine. An unauthenticated remote attacker can exploit this vulnerability by providing unvalidated user input to the template engine. This bypasses existing security mechanisms, allowing for the execution of unauthorized expressions and leading to Server-Side Template Injection (SSTI).
Remediation
Before applying this update, make sure all previously released errata relevant to your system have been applied. For details on how to apply this update, refer to: https://access.redhat.com/articles/11258
Optional official sources

National CERT insights
?CERT means Computer Emergency Response Team; CSIRT is the closely related term Computer Security Incident Response Team.

Select the national-authority views to include. The exact source language is shown on each matched advisory. Your choice is remembered on this device and encoded in the shareable URL.

Official European source

ENISA European Vulnerability Database

Official EUVD identifiers, advisory evidence and known-exploited context. Missing fields are not treated as evidence of low risk.

1 current
ENISA EUVD identifier

EUVD-2026-23573

No EUVD known-exploited evidence

ENISA has published the identifier mapping but no EUVD description has been stored yet.

EUVD state
Present in the current official mapping
Known exploitation
Not present in the current ENISA EUVD known-exploited dataset. This is not proof of no exploitation.
ENISA score
Not supplied in the stored EUVD record
Advisory evidence
No linked advisory details stored yet
Recommended actionWithin 72 hours

Critical technical impact with a remotely reachable, unauthenticated path; no CISA KEV confirmation is currently recorded.

Patch available
01

What, why and how

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.

What

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.

Why

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.

How

An attacker operating through a network path may attempt exploitation without authentication or user interaction. If successful, the issue may cause the confidentiality, integrity or availability impact described by the vendor.

What

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.

Why

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.

How

An attacker operating through a network path may attempt exploitation without authentication or user interaction. If successful, the issue may cause the confidentiality, integrity or availability impact described by the vendor.

02

Exploit reality and attack path

CVSS severity, EPSS forecast probability, public exploit material and CISA-confirmed exploitation are separate signals.

Observed exploitation
?Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.
No confirmed evidence

No CISA KEV match was present at the last successful refresh. This means no confirmation from that source, not proof of no exploitation.

Public PoC / exploit material
?Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.
None recorded

No exploit-tagged reference or CISA SSVC proof-of-concept state is currently recorded. Research may still exist outside the structured feeds.

Likely attack path
a network path → Improper Neutralization of Special Elements used in an Expression Language Statement ('Expression Language Injection') → cause the confidentiality, integrity or availability impact described by the vendor
Attack surface
Network
Privileges required
None: unauthenticated exploitation is possible
User interaction
None
Attack complexity
High: exploitation depends on specific conditions
Security boundary
Changed: exploitation can affect a different security authority
Weakness
?CWE means Common Weakness Enumeration: a standard category for the underlying weakness.
CWE-917 ↗

CWE-917: 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.

CVSS vector
?CVSS means Common Vulnerability Scoring System. The vector records the metric values used to calculate technical severity.
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H

Common Vulnerability Scoring System 3.1: the compact vector below is decoded into plain language.

AVNetworkAttack vector: The vulnerable component can be reached over a network.ACHighAttack complexity: Successful exploitation depends on specific conditions outside the attacker's direct control.PRNonePrivileges required: The attacker does not need an account or existing privileges.UINoneUser interaction: No action by another user is required.SChangedScope: The attack can affect a component governed by a different security authority.CHighConfidentiality impact: A successful attack can cause a major loss.IHighIntegrity impact: A successful attack can cause a major loss.AHighAvailability impact: A successful attack can cause a major loss.
Post-exploitation / living off the land
No specific living-off-the-land technique is confirmed in the structured sources. Monitor normal administration tools for activity inconsistent with the affected service's baseline.
NetworkUnauthenticatedCWE-917
A

Official authority intelligence

Only matched European and national findings are included. Language selectors and unavailable sources are omitted.

03

Patch and workaround

Operational remediation based on structured source evidence.

Status
?Patch availability is based on structured fixed-version fields and authoritative update references. If no fix is verified, check the vendor advisory before making a change.
Patch available
Affected
thymeleaf as a component of Red Hat Fuse 7; spring-boot-starter-thymeleaf as a component of Red Hat Single Sign-On 7; thymeleaf as a component of Red Hat Single Sign-On 7; thymeleaf-extras-java8time as a component of Red Hat Single Sign-On 7; thymeleaf-spring5 as a component of Red Hat Single Sign-On 7
Fixed
registry.redhat.io/devspaces/openvsx-rhel9@sha256:341c8f0f91bd41d4bded00443cd7ab2ddab4972a5ee1ddff4dcbfcdd5c2764f4_arm64 as a component of Red Hat OpenShift Dev Spaces 3.28; registry.redhat.io/devspaces/openvsx-rhel9@sha256:94d4124c7884916fbce4af4655b8a5eef5b62df6a21afabf6461bbb898d895b9_ppc64le as a component of Red Hat OpenShift Dev Spaces 3.28; registry.redhat.io/devspaces/openvsx-rhel9@sha256:e9eef99fc45b2ce06fadacf3db85e6e2f1fbabb16afc250929387ce2589732c3_amd64 as a component of Red Hat OpenShift Dev Spaces 3.28; registry.redhat.io/devspaces/openvsx-rhel9@sha256:fe8c450b4f48bd6935495464a3c2a7bfcf29e2bee04d44f9e60344351c49b049_s390x as a component of Red Hat OpenShift Dev Spaces 3.28; registry.redhat.io/devspaces/pluginregistry-rhel9@sha256:5f22f4a4c2de62f4569dcfbdf3650edc51aacee3b4cb6c49c87b25c6bf530b6c_amd64 as a component of Red Hat OpenShift Dev Spaces 3.28; registry.redhat.io/devspaces/pluginregistry-rhel9@sha256:82fe544aa4f03ca665ad23acbb5472032ccdb04fc9e96d77b3b8e764e544f846_arm64 as a component of Red Hat OpenShift Dev Spaces 3.28; registry.redhat.io/devspaces/pluginregistry-rhel9@sha256:d0250c5ec7cd6f6a1584680bb23a9b86c7791a8b8176561b9d093301d41a6218_s390x as a component of Red Hat OpenShift Dev Spaces 3.28; registry.redhat.io/devspaces/pluginregistry-rhel9@sha256:e16a96851641fe2f7a92889a3ca6e8357d4a8f762bdd5b6116332965fdbd3a19_ppc64le as a component of Red Hat OpenShift Dev Spaces 3.28
Action
Before applying this update, make sure all previously released errata relevant to your system have been applied. For details on how to apply this update, refer to: https://access.redhat.com/articles/11258
Workaround
No verified workaround is recorded. If business-safe, reduce exposure to the affected interface and allow only trusted sources until authoritative guidance is available.
04

Evidence and provenance

Published 17 Apr 2026 · Last source change 18 Aug 2026, 12:05 UTC · CWE-917 · Improper Neutralization of Special Elements used in an Expression Language Statement ('Expression Language Injection')

CVE recordCVE.org · 5.2
CVSS sourceCNA
EPSS source
?The date BlackTree first stored a score for this CVE from the daily FIRST EPSS feed.
FIRST · tracked since 2026-08-14
European sourceENISA EUVD · EUVD-2026-23573
Product sourceVendor CSAF · Red Hat Product Security
Remediation sourceVendor CSAF · Red Hat Product Security
CWE sourceCNA
NVD statusNVD modified after enrichment

Core structured fields are present and their contributing authorities are shown above.

Material change intelligence

What changed after publication

View recent updates →

No material field changes have been recorded since change tracking began. Routine source refreshes and cosmetic edits are intentionally excluded.

Material fields only · duplicate refreshes suppressed · history retained for the configured operational retention period
CVE published
Fixed release or patch reference recorded
ENISA EUVD · EUVD-2026-23573↗Vendor CSAF · Red Hat Product Security↗CVE authority or vendor reference↗Official CVE record (CNA and ADP data)↗NVD record↗
Technical terms and abbreviations used in this report
CVE
Common Vulnerabilities and Exposures: the public identifier for one disclosed vulnerability.
CVSS
Common Vulnerability Scoring System: a technical severity framework; it is not patching priority by itself.
EPSS
Exploit Prediction Scoring System: FIRST's estimate of the probability that exploitation activity will be observed in the next 30 days; it is a forecast, not confirmation.
CWE
Common Weakness Enumeration: the standard category describing the underlying software or hardware weakness.
CNA
CVE Numbering Authority: an organisation authorised to assign and publish CVE records.
CISA ADP
Cybersecurity and Infrastructure Security Agency Authorized Data Publisher: structured enrichment added to a CVE record.
NVD
National Vulnerability Database: NIST's enrichment service for CVE records.
CERT / CSIRT
A computer security incident response team that publishes warnings or coordinates incident response.
PoC
Proof of concept: public material that demonstrates or helps reproduce exploitation.
CSAF
Common Security Advisory Framework: a machine-readable format for security advisories.
LoTL
Living off the land: abuse of legitimate tools or system functions during an attack.
Free version - for non-commercial use only.CVE-2026-40478 · cve.blacktree.nl