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CVE-2026-40478 is a server-side template injection vulnerability in Thymeleaf 3.1.3.RELEASE and earlier, including the core, Spring 5, and Spring 6 integration artifacts. Thymeleaf expression-execution protections inadequately neutralize certain syntax patterns. In SpringTemplateEngine/SpEL use cases, a parsing mismatch allowed alternate whitespace after the SpEL object-instantiation keyword to evade a check expecting an ASCII space. Type restrictions also incompletely blocked dangerous classes outside the java.* namespace. Where attacker-controlled data reaches expression text, view names, fragment selectors, or another Thymeleaf-parsed channel, an unauthenticated attacker can cause unauthorized expression evaluation.
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What an attacker gets, and what they’ve been doing with it.
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No public exploit code observed for this vulnerability.
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Vendor-confirmed product mapping. Mallory continuously reconciles this list against your asset inventory.
12 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.
A critical Thymeleaf sandbox bypass enabling arbitrary code execution in Spring applications, mentioned as broader ecosystem context rather than the main subject.
A specific Thymeleaf template injection vulnerability discussed in the referenced post/article; the content suggests its impact depends on deployment or usage conditions.
A security bypass vulnerability in Thymeleaf's expression execution mechanisms that can allow unauthenticated remote attackers to achieve server-side template injection (SSTI) when unvalidated user input is passed directly to the template engine.
A critical server-side template injection vulnerability in Thymeleaf 3.1.3 and earlier that allows bypass of built-in protections via whitespace parsing and incomplete type blocklisting, enabling arbitrary expression execution, file writes, and potential remote code execution in Spring-based applications.
Query your assets running an affected version, and investigate the blast radius.
Every observed campaign linking this CVE to a named adversary.
Malware families riding this exploit, with evidence and IOCs.
YARA, Sigma, Snort, and vendor rules, auto-deployed to your SIEM.
Cross-references every affected SKU, including bundled OEM variants.
Community discussion across Reddit, Mastodon, and other social sources.