CVE-2026-41901
CRITICALCVE-2026-41901 is a critical-severity (CVSS 9) Expression Language Injection vulnerability in org.thymeleaf:thymeleaf. O3 Security confirms whether CVE-2026-41901 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
Thymeleaf: Improper recognition of unauthorized syntax patterns in sandboxed Thymeleaf expressions
Blast Radius
org.thymeleaf:thymeleaf☕org.thymeleaf:thymeleaf-spring5☕org.thymeleaf:thymeleaf-spring6Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Maven packages — download data is not available via public APIs for these ecosystems.
Description
Thymeleaf is a server-side Java template engine for web and standalone environments. Prior to 3.1.5.RELEASE, a security bypass vulnerability exists in the expression execution mechanisms of Thymeleaf. 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). This vulnerability is fixed in 3.1.5.RELEASE.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| ☕Maven | org.thymeleaf:thymeleaf | all versions | 3.1.5.RELEASE |
| ☕Maven | org.thymeleaf:thymeleaf-spring5 | all versions | 3.1.5.RELEASE |
| ☕Maven | org.thymeleaf:thymeleaf-spring6 | all versions | 3.1.5.RELEASE |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for org.thymeleaf:thymeleaf. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update org.thymeleaf:thymeleaf to 3.1.5.RELEASE or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-41901 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether CVE-2026-41901 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to CVE-2026-41901. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2026-41901 in your dependencies?
O3 detects CVE-2026-41901 across Maven dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.