A recently identified critical vulnerability in HubSpot’s open-source Jinjava template engine poses a significant threat to thousands of websites. This flaw, designated as CVE-2025-59340, allows attackers to bypass sandbox restrictions and execute arbitrary code remotely on affected systems. The vulnerability affects all Jinjava versions prior to 2.8.1 and has been assigned a CVSS v3.1 score of 10.0, indicating its severity.
Understanding the Vulnerability
Jinjava is a widely used template engine that enables dynamic content rendering in web applications. To maintain security, it employs a sandbox environment designed to restrict potentially dangerous operations, such as invoking the `getClass()` method or directly instantiating `Class` objects. However, security researchers have discovered a method to circumvent these protections.
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. This manipulation allows the deserialization of attacker-controlled input into instances like `java.net.URL`, enabling unauthorized reading of local files.
The core issue lies in the fact that `JavaType` construction is not blacklisted within the sandbox. This oversight permits the instantiation of semi-arbitrary classes, opening avenues for Server-Side Request Forgery (SSRF), arbitrary file reads, and, when combined with additional exploits, remote code execution (RCE).
Scope of Impact
The vulnerability affects production applications that integrate Jinjava via Maven coordinates `com.hubspot.jinjava:jinjava` in versions older than 2.8.1. This includes a vast array of content management systems, email template renderers, and custom web applications that rely on dynamic template rendering. Given the widespread adoption of Jinjava, the number of potentially vulnerable websites is substantial.
Exploitation of this vulnerability requires no user interaction and can be executed over a network with low complexity, without the need for any privileges. This ease of exploitation further amplifies the risk associated with the flaw.
Risk Factors:
– Affected Products: `com.hubspot.jinjava:jinjava` versions prior to 2.8.1
– Impact: Sandbox escape, arbitrary file reads, SSRF, potential remote code execution
– Exploit Prerequisites: Network access; no privileges; no user interaction
– CVSS 3.1 Score: 9.8 (Critical)
Mitigation Measures
In response to this critical vulnerability, HubSpot has released Jinjava version 2.8.1, which introduces explicit restrictions on `JavaType` usage. The update blocks the `constructFromCanonical` method for untrusted inputs and reinforces the blacklist in `JinjavaBeanELResolver`.
Administrators are strongly urged to upgrade to Jinjava 2.8.1 immediately. Additionally, it is essential to audit template code for any direct or indirect use of the `____int3rpr3t3r____` variable to ensure that no potential exploitation vectors remain.
Security teams should also review their dependency graphs to identify other libraries that expose 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 strengthen defenses against similar template engine vulnerabilities.
By proactively applying these patches and tightening sandbox controls, organizations can prevent unauthorized file access, SSRF, and potential remote code execution resulting from deserialization chains in Jinjava.
