CVE-2026-40477

Description

### Impact A security bypass vulnerability exists in the expression execution mechanisms of Thymeleaf up to and including 3.1.3.RELEASE. 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). ### Patches This has been fixed in Thymeleaf 3.1.4.RELEASE. ### Workarounds No workaround is available beyond ensuring applications do not pass unvalidated user input directly to the template engine. Upgrading to 3.1.4.RELEASE is strongly recommended in any case. ### Credits Thanks to Thomas Reburn (Praetorian) for responsible disclosure.

How to fix CVE-2026-40477

To remediate CVE-2026-40477, upgrade the affected package to a fixed version below.

• —upgrade to 3.1.4.RELEASE or later
• —upgrade to 3.1.4.RELEASE or later
• —upgrade to 3.1.4.RELEASE or later

Is CVE-2026-40477 being exploited?

Low — EPSS is 0.1%, meaning exploitation activity has not been observed at scale.

Affected packages (3)

• from 0, < 3.1.4.RELEASE
• from 0, < 3.1.4.RELEASE
• from 0, < 3.1.4.RELEASE

CVSS scores

References (3)

• ADVISORYnvd.nist.gov/vuln/detail/CVE-2026-40477
• PATCHgithub.com/thymeleaf/thymeleaf
• WEBgithub.com/thymeleaf/thymeleaf/security/advisories/GHSA-r4v4-5mwr-2fwr