CVE-2025-59340 is a critical vulnerability affecting versions of HubSpot's jinjava template engine prior to 2.8.1. Jinjava is a Java-based template engine that adapts Django template syntax to render Jinja templates. The vulnerability arises from improper neutralization of special elements used in the template engine, specifically related to the deserialization process within the ObjectMapper component. By leveraging the method mapper.getTypeFactory().constructFromCanonical(), an attacker can manipulate the deserialization process to instantiate arbitrary Java classes without invoking restricted methods or class literals directly. This bypasses the sandbox restrictions intended to isolate template execution. One notable exploitation vector involves instantiating classes such as java.net.URL, which can be used to access local files (e.g., file:///etc/passwd) or remote URLs. This capability can be further chained to achieve remote code execution (RCE), allowing an attacker to execute arbitrary code on the host system. The vulnerability has a CVSS 3.1 base score of 9.8, indicating critical severity, with network attack vector, no required privileges or user interaction, and high impact on confidentiality, integrity, and availability. Although no known exploits are currently reported in the wild, the potential for severe damage is significant. The issue is resolved in jinjava version 2.8.1, which includes fixes to prevent unsafe deserialization and sandbox escape.

For European organizations, the impact of this vulnerability can be severe. Organizations using jinjava in their web applications or services risk unauthorized data disclosure, including access to sensitive local files, which can lead to leakage of credentials, configuration files, or personal data protected under GDPR. The ability to achieve remote code execution could allow attackers to take full control of affected servers, leading to data breaches, service disruptions, or use of compromised systems as a foothold for further attacks within the network. This could result in significant operational downtime, reputational damage, and regulatory penalties. Sectors such as finance, healthcare, government, and critical infrastructure, which often rely on Java-based web applications, are particularly at risk. The vulnerability’s ease of exploitation over the network without authentication or user interaction increases the likelihood of attacks targeting exposed services. Given the critical nature of the flaw, organizations that have not updated to jinjava 2.8.1 or implemented mitigations remain highly vulnerable.

European organizations should immediately audit their software inventories to identify any use of jinjava versions prior to 2.8.1. The primary mitigation is to upgrade all instances of jinjava to version 2.8.1 or later, which contains the patch preventing unsafe deserialization and sandbox escapes. If immediate upgrade is not feasible, organizations should implement strict input validation and sanitization on all data passed to the template engine to reduce the risk of malicious payloads. Employing runtime application self-protection (RASP) or web application firewalls (WAFs) with custom rules to detect and block suspicious deserialization patterns can provide interim protection. Additionally, running applications with the least privilege necessary and isolating template rendering environments can limit the impact of a successful exploit. Monitoring application logs for unusual deserialization activity and network connections initiated by the application can help detect exploitation attempts. Finally, organizations should ensure robust incident response plans are in place to quickly address any compromise resulting from this vulnerability.