CVE-2025-59340: HubSpot Jinjava RCE Vulnerability

CVE-2025-59340 Overview

CVE-2025-59340 is a critical sandbox escape vulnerability in Jinjava, a Java-based template engine that implements Django/Jinja template syntax. The vulnerability allows attackers to bypass the template sandbox by exploiting the mapper.getTypeFactory().constructFromCanonical() method, enabling the deserialization of attacker-controlled input into arbitrary Java classes. This can lead to local file access, server-side request forgery, and potentially remote code execution through class instantiation chains.

Critical Impact

Attackers can escape the Jinjava sandbox to instantiate arbitrary Java classes, enabling access to local files (e.g., /etc/passwd), internal URLs, and with further exploitation chaining, achieve remote code execution on affected systems.

Affected Products

• HubSpot Jinjava versions prior to 2.8.1
• Applications using vulnerable Jinjava versions for template rendering
• Systems exposing Jinjava template processing to untrusted input

Discovery Timeline

• 2025-09-17 - CVE-2025-59340 published to NVD
• 2025-09-26 - Last updated in NVD database

Technical Details for CVE-2025-59340

Vulnerability Analysis

This vulnerability represents a critical sandbox escape in the Jinjava template engine. The flaw exists in how the underlying Jackson ObjectMapper handles type construction through the constructFromCanonical() method. By exploiting this mechanism, attackers can instruct the ObjectMapper to deserialize attacker-controlled input into arbitrary Java classes, effectively bypassing the sandbox restrictions that should prevent access to dangerous system functionality.

The vulnerability is particularly severe because it enables semi-arbitrary class instantiation without directly invoking restricted methods or class literals. This means traditional sandbox restrictions that block direct access to dangerous classes like java.lang.Runtime or java.lang.ProcessBuilder can be circumvented through indirect instantiation.

Root Cause

The root cause is classified under CWE-1336 (Improper Neutralization of Special Elements Used in a Template Engine). The Jinjava template engine's bean resolution mechanism failed to properly validate and restrict class types before allowing property access. The JinjavaBeanELResolver class did not check whether the base object belonged to a restricted class before processing property access requests, allowing attackers to chain method calls on arbitrary objects including sensitive Java system classes.

Attack Vector

The attack is network-accessible and requires no authentication or user interaction. An attacker can exploit this vulnerability by:

1. Crafting a malicious Jinja template that leverages the mapper.getTypeFactory().constructFromCanonical() pattern
2. Specifying arbitrary Java class names to be instantiated (e.g., java.net.URL)
3. Using instantiated objects to access local files via file:// URLs or make HTTP requests to internal services
4. Chaining additional class instantiations to escalate from information disclosure to remote code execution

For example, an attacker could instantiate java.net.URL with a file:///etc/passwd parameter to read sensitive system files, or target internal services for SSRF attacks.

  @Override
  public Object getValue(ELContext context, Object base, Object property) {
+    if (isRestrictedClass(base)) {
+      return null;
+    }
    Object result = super.getValue(context, base, validatePropertyName(property));
    return result instanceof Class ? null : result;
  }

Source: GitHub Commit 66df351e7e8ad71ca04dcacb4b65782af820b8b1

The patch adds a critical check using isRestrictedClass(base) to prevent property access on restricted class types, returning null instead of allowing the operation to proceed.

Detection Methods for CVE-2025-59340

Indicators of Compromise

• Template inputs containing references to getTypeFactory() or constructFromCanonical() method calls
• Unusual file access patterns from Java processes, particularly reads of /etc/passwd or other sensitive system files
• Outbound HTTP connections originating from template processing components to internal or unexpected destinations
• Java stack traces showing ObjectMapper deserialization of unexpected class types within Jinjava execution contexts

Detection Strategies

• Implement application-level logging for all template rendering operations and monitor for suspicious patterns
• Deploy Web Application Firewall (WAF) rules to detect and block template injection payloads containing Java reflection patterns
• Monitor for process behavior anomalies including unexpected file reads or network connections from Jinjava-dependent services
• Enable Java Security Manager logging to detect attempts to instantiate restricted classes

Monitoring Recommendations

• Configure alerting for template processing errors that indicate blocked sandbox escape attempts
• Monitor application logs for Jackson ObjectMapper type construction activities involving system or network classes
• Implement network traffic analysis to detect SSRF attempts originating from application servers
• Review access logs for patterns consistent with file disclosure exploitation (sequential requests, known sensitive file paths)

How to Mitigate CVE-2025-59340

Immediate Actions Required

• Upgrade HubSpot Jinjava to version 2.8.1 or later immediately
• Audit all applications that expose Jinjava template processing to user-controlled input
• Implement input validation to reject templates containing suspicious patterns until patching is complete
• Review application logs for evidence of exploitation attempts

Patch Information

HubSpot has released Jinjava version 2.8.1 which addresses this vulnerability. The fix adds class restriction checks in the JinjavaBeanELResolver to prevent property access on restricted class types.

• Fixed Version:2.8.1
• Patch Commit:GitHub Commit 66df351e7e8ad71ca04dcacb4b65782af820b8b1
• Release Notes:GitHub Release Version 2.8.1
• Security Advisory:GHSA-m49c-g9wr-hv6v

Workarounds

• Restrict template processing to trusted administrators only until the patch can be applied
• Implement network segmentation to limit the impact of potential SSRF exploitation
• Deploy additional sandbox restrictions at the application level to block instantiation of dangerous classes
• Use Web Application Firewall rules to filter requests containing known exploitation patterns

# Maven dependency update for Jinjava
# Update pom.xml to use patched version
<dependency>
    <groupId>com.hubspot.jinjava</groupId>
    <artifactId>jinjava</artifactId>
    <version>2.8.1</version>
</dependency>