HubSpot’s Jinjava Engine Flaw Exposes Thousands of Sites to RCE Attacks

A critical security vulnerability has been discovered in HubSpot’s Jinjava template engine, potentially exposing thousands of websites and applications to remote code execution attacks.

The flaw, tracked as CVE-2025-59340, carries the maximum CVSS score of 10.0, indicating the severity of the security risk.

Sandbox Bypass Enables Dangerous Exploits

The vulnerability stems from a sandbox bypass mechanism that allows attackers to circumvent the engine’s built-in security restrictions.

Jinjava’s sandbox was designed to prevent direct access to dangerous methods like getClass() and block instantiation of Class objects.

CVE ID	Affected Product	CVSS 3.1 Score	Impact
CVE-2025-59340	HubSpot Jinjava Template Engine	10.0 (Critical)	Sandbox bypass leading to RCE, file access, SSRF

However, security researchers discovered that these protections can be bypassed through JavaType-based deserialization.

Attackers can exploit the built-in ____int3rpr3t3r____ variable, which provides direct access to the jinjavaInterpreter instance.

By traversing to the config field and accessing the underlying ObjectMapper, malicious actors can invoke readValue() with attacker-controlled input to instantiate arbitrary classes.

This technique leverages the constructFromCanonical() method to create semi-arbitrary class instances without triggering restricted method protections.

The vulnerability particularly affects applications running Jinjava versions prior to 2.8.1, with the patched version 2.8.1 now available to address the security flaw.

The attack requires network access but demands no special privileges or user interaction, making it easily exploitable by remote attackers. The impact of this vulnerability extends far beyond simple sandbox escapes.

Successful exploitation enables attackers to read arbitrary files from the server filesystem, perform Server-Side Request Forgery attacks, and potentially achieve complete remote code execution depending on the target environment’s available classes.

Security researchers demonstrated the vulnerability’s severity by showing how attackers can instantiate java.net.URL objects to read sensitive system files like /etc/passwd.

The proof-of-concept exploit reveals how the flaw can be chained with other techniques to escalate privileges and gain unauthorized access to critical system resources.

Organizations using HubSpot’s Jinjava template engine should immediately upgrade to version 2.8.1 or later to mitigate this critical vulnerability.

The flaw was responsibly disclosed by security researchers taisehub and odgrso, allowing HubSpot to develop and release a patch before public disclosure.

System administrators should audit their applications for Jinjava usage and prioritize patching efforts given the vulnerability’s critical severity rating and ease of exploitation.

The weakness falls under CWE-1336, highlighting improper neutralization of special elements used in template engines, a common security pitfall in web application development.

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