CVE-2025-59340 is a critical security vulnerability affecting versions of the HubSpot 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. By leveraging the method mapper.getTypeFactory().constructFromCanonical(), an attacker can manipulate the underlying ObjectMapper to deserialize attacker-controlled input into arbitrary Java classes. This deserialization bypasses sandbox restrictions, allowing the instantiation of classes such as java.net.URL. This capability enables attackers to access local files (e.g., file:///etc/passwd) and external URLs, potentially leading to information disclosure. More critically, with further exploitation and chaining of this primitive, remote code execution (RCE) is possible. The vulnerability is classified under CWE-1336, which concerns improper neutralization of special elements in template engines, leading to injection and deserialization flaws. The vulnerability has a CVSS v3.1 score of 9.8, indicating a critical severity with network attack vector, no required privileges or user interaction, and high impact on confidentiality, integrity, and availability. The flaw was publicly disclosed on September 17, 2025, and fixed in jinjava version 2.8.1. No known exploits are currently reported in the wild, but the ease of exploitation and severity suggest a high risk if unpatched.

For European organizations, this vulnerability poses a significant risk, especially those using jinjava in their web applications or services. Exploitation can lead to unauthorized access to sensitive internal files and data, compromising confidentiality. The potential for remote code execution could allow attackers to take full control of affected systems, leading to data breaches, service disruption, and lateral movement within networks. Organizations in sectors such as finance, healthcare, government, and critical infrastructure are particularly vulnerable due to the sensitive nature of their data and the potential for severe operational impact. Additionally, the vulnerability’s network-exploitable nature means attackers can target exposed services remotely without authentication, increasing the attack surface. Given the high severity and the ability to bypass sandboxing, exploitation could facilitate advanced persistent threats (APTs) or ransomware campaigns targeting European entities. The lack of known exploits currently provides a window for proactive mitigation, but the critical nature demands immediate attention.

European organizations should promptly identify all instances of jinjava in their environments and verify the version in use. Immediate upgrade to version 2.8.1 or later is essential to remediate the vulnerability. Where upgrading is not immediately feasible, organizations should implement strict input validation and sanitization on all data passed to the template engine to reduce the risk of malicious payloads. Network-level protections such as web application firewalls (WAFs) should be configured to detect and block suspicious payloads targeting template deserialization. Employing runtime application self-protection (RASP) solutions can help detect and prevent exploitation attempts in real time. Additionally, organizations should audit and restrict permissions of the Java runtime environment to limit the impact of potential exploitation, such as sandboxing the application process and restricting network and file system access. Regular security assessments and code reviews focusing on deserialization and template injection risks should be conducted. Finally, monitoring logs for unusual access patterns or errors related to template processing can provide early detection of exploitation attempts.