Overview
In the current landscape of cybersecurity, any vulnerability can lead to serious consequences, especially when it comes to web application technologies. This blog post will address a critical vulnerability in jinjava, a Java-based template engine. Jinjava, widely used for rendering jinja templates, has been identified to contain a severe vulnerability (CVE-2025-59340) that can lead to remote code execution (RCE). This vulnerability affects all versions of jinjava prior to 2.8.1, potentially impacting a large number of applications and systems worldwide. The severity of this vulnerability underscores the need for immediate attention and remediation.
Vulnerability Summary
CVE ID: CVE-2025-59340
Severity: Critical (CVSS: 9.8)
Attack Vector: Network
Privileges Required: None
User Interaction: None
Impact: Potential system compromise or data leakage
Affected Products
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Product | Affected Versions
Jinjava | Prior to 2.8.1
How the Exploit Works
The vulnerability resides in how jinjava interacts with the underlying ObjectMapper. By calling mapper.getTypeFactory().constructFromCanonical(), an attacker can instruct ObjectMapper to deserialize their input into arbitrary classes. This allows the creation of semi-arbitrary class instances without directly invoking restricted methods or class literals. As a result, an attacker can escape the sandbox and instantiate classes such as java.net.URL, leading to potential access to local files and URLs (e.g., file:///etc/passwd). With further chaining, this primitive can potentially lead to remote code execution.
Conceptual Example Code
Here is a conceptual example of how this vulnerability might be exploited:
String payload = "{ \"__type__\": \"java.net.URL\", \"val\": \"file:///etc/passwd\" }";
ObjectMapper mapper = new ObjectMapper();
mapper.getTypeFactory().constructFromCanonical(payload);In this example, the attacker submits a JSON string that instructs the ObjectMapper to construct an instance of java.net.URL with the value “file:///etc/passwd”, potentially leading to unauthorized access to sensitive system files.
Mitigation Guidance
To mitigate this vulnerability, it is recommended to apply the vendor patch immediately. Users should upgrade to jinjava version 2.8.1 or later, which contains a fix for this vulnerability. In the meantime, using a Web Application Firewall (WAF) or Intrusion Detection System (IDS) can provide temporary mitigation. However, these measures should not replace the need for patching and upgrading the vulnerable software.
