Bug 2459344 (CVE-2026-40477)

Summary:	CVE-2026-40477 thymeleaf: Thymeleaf: Server-Side Template Injection via security bypass in expression execution
Product:	[Other] Security Response	Reporter:	OSIDB Bzimport <bzimport>
Component:	vulnerability	Assignee:	Product Security DevOps Team <prodsec-dev>
Status:	NEW ---	QA Contact:
Severity:	high	Docs Contact:
Priority:	high
Version:	unspecified	CC:	aschwart, asoldano, aszczucz, bbaranow, bmaxwell, boliveir, bstansbe, dlofthou, drichtar, fmariani, gmalinko, istudens, ivassile, iweiss, janstey, mosmerov, mposolda, msvehla, nwallace, pberan, pdelbell, pesilva, pjindal, pmackay, rmartinc, rstancel, rstepani, sdawley, smaestri, ssilvert, sthorger, tcunning, thjenkin, vdosoudi, vmuzikar, yfang
Target Milestone:	---	Keywords:	Security
Target Release:	---
Hardware:	All
OS:	Linux
Whiteboard:
Fixed In Version:		Doc Type:	---
Doc Text:	A flaw was found in Thymeleaf, a server-side Java template engine. An unauthenticated remote attacker can exploit a security bypass vulnerability in the expression execution mechanisms. By providing unvalidated user input directly to the template engine, the attacker can bypass the library's protections, leading to Server-Side Template Injection (SSTI). This allows access to potentially sensitive objects from within a template.	Story Points:	---
Clone Of:		Environment:
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Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:

Description OSIDB Bzimport 2026-04-17 23:01:15 UTC

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.