HubSpot’s Jinjava Engine Vulnerability Exposes Thousands of Websites to RCE Attacks

A newly disclosed flaw in HubSpot’s open-source Jinjava template engine could allow attackers to bypass sandbox restrictions and achieve remote code execution (RCE) on thousands of websites relying on versions prior to 2.8.1. 

Tracked as CVE-2025-59340 and rated Critical with a CVSS v3.1 score of 10.0, the issue stems from JavaType‐based deserialization, enabling threat actors to instantiate arbitrary classes despite existing protections.

Jinjava Sandbox Escape

Jinjava’s sandbox is designed to block dangerous calls like getClass() and forbid direct instantiation of Class objects. 

However, security researchers discovered that by accessing the built-in ____int3rpr3t3r____ variable, which exposes the active JinjavaInterpreter instance, an attacker can navigate to the internal ObjectMapper and invoke its unrestricted readValue method. 

Attackers can deserialize attacker-controlled input into instances like java.net.URL and read local files. 

Because JavaType construction is not blacklisted, the sandbox escape enables the instantiation of semi-arbitrary classes. This primitive opens paths for full SSRF, arbitrary file reads, and—when chained with additional gadgets—RCE.

Production applications integrating Jinjava via Maven coordinates com.hubspot.jinjava:jinjava in versions older than 2.8.1 are vulnerable. 

Thousands of content management systems, email template renderers, and custom web applications that employ dynamic template rendering may be at risk. 

Exploitation requires no user interaction and carries a Network attack vector with Low complexity and no privileges required.

Mitigation

To address the issue, HubSpot released jinjava 2.8.1, which adds explicit restrictions on JavaType usage, blocking constructFromCanonical for untrusted inputs and reinforcing the blacklist in JinjavaBeanELResolver. 

Administrators are urged to upgrade immediately and audit template code for any direct or indirect use of ____int3rpr3t3r____.

Security teams should also review their dependency graphs for other libraries exposing Jackson’s ObjectMapper without adequate type restrictions. 

Implementing strict input validation, disabling default typing where feasible, and applying runtime instrumentation to detect suspicious deserialization calls can further harden defenses against similar template engine bypasses.

By proactively patching and tightening sandbox controls, organizations can prevent unauthorized file access, SSRF, and potential RCE stemming from deserialization chains in Jinjava.

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