CVE-2026-25526: 
Java vulnerability analysis and mitigation

CVE-2026-25526 is a critical sandbox bypass and remote code execution vulnerability in HubSpot's Jinjava, a Java-based Jinja template engine. It affects Jinjava versions prior to 2.7.6 and versions 2.8.0 through 2.8.2 (prior to 2.8.3). The vulnerability was disclosed on February 3, 2026 via a GitHub Security Advisory, with NVD publication on February 4, 2026. It carries a CVSS v3.1 base score of 9.8 (Critical) (GitHub Advisory, Feedly).

The vulnerability stems from two distinct sandbox bypass flaws classified under CWE-1336 (Improper Neutralization of Special Elements Used in a Template Engine). First, the ForTag class bypasses JinjavaBeanELResolver restrictions by iterating over object properties using Introspector.getBeanInfo() and directly invoking getter methods via PropertyDescriptor.getReadMethod() without enforcing sandbox access controls. Second, the sandbox's type allowlist can be circumvented by leveraging ObjectMapper to instantiate arbitrary Java classes through JSON deserialization — including restricted types like JinjavaELContext and JinjavaConfig — because the Jackson databind package was not included in the restricted class denylist. The fix in commits 3d02e50 and c7328dc routes ForTag property access through interpreter.resolveProperty() (which enforces sandbox checks) and adds com.fasterxml.jackson.databind to the restricted package list (GitHub Advisory, Patch Commit).

Successful exploitation allows an attacker with template creation or editing privileges to access arbitrary getter methods on objects in the template context, instantiate arbitrary Java classes by bypassing the type allowlist, and read sensitive files from the server filesystem (e.g., /etc/passwd). In the worst case, this leads to full remote code execution on the host running the Jinjava engine, with potential for complete confidentiality, integrity, and availability compromise. Any system rendering untrusted Jinja templates via Jinjava — including HubSpot CMS integrations and custom applications — is at risk of data exfiltration and server takeover (GitHub Advisory, Feedly).

A public proof-of-concept exploit is available on GitHub at av4nth1ka/jinjava-cve-2026-25526-poc, published around March 2, 2026 (PoC). As of the time of reporting, there is no confirmed evidence of in-the-wild exploitation, and no threat actor attribution has been made (Feedly). The EPSS score is approximately 0.097%, indicating currently low but non-negligible exploitation probability. The vulnerability is not listed in the CISA KEV catalog at this time, though CISA referenced it in a weekly vulnerability bulletin (CISA Bulletin). Qualys has added multiple detection signatures for this CVE.

1. Identify target: Locate applications that render user-controlled Jinja templates using HubSpot's Jinjava library (versions < 2.7.6 or 2.8.0–2.8.2), such as HubSpot CMS custom modules or Java applications using Jinjava as a templating engine.
2. Gain template access: Obtain the ability to create or edit a Jinja template in the target system — this may require a low-privilege user account or may be available to unauthenticated users depending on the application's access controls.
3. Exploit ForTag bypass: Craft a malicious template using a {% for %} loop that iterates over a sensitive object (e.g., the internal interpreter context ____int3rpr3t3r____) to access restricted getter methods that would normally be blocked by JinjavaBeanELResolver:

   {% for _, config, class in ____int3rpr3t3r____ %}{{ class }}{% endfor %}

4. Instantiate ObjectMapper: Use the ForTag bypass to obtain an ObjectMapper instance and call enableDefaultTyping() to enable polymorphic deserialization, bypassing the type allowlist.
5. Instantiate restricted classes: Use the enabled ObjectMapper to deserialize JSON payloads that instantiate arbitrary Java classes, including those on the sandbox denylist.
6. Read files or execute code: Leverage the instantiated classes to read sensitive server files (e.g., /etc/passwd) or chain further Java gadgets to achieve arbitrary code execution on the server (GitHub Advisory, PoC).

• Logs: Application logs showing template rendering errors related to JinjavaBeanELResolver, ForTag, or ObjectMapper; unexpected PropertyDescriptor or Introspector class references in Java stack traces during template rendering.
• Network: Unusual outbound connections from the Java application server to external hosts following template rendering requests; HTTP requests submitting templates containing ____int3rpr3t3r____, ObjectMapper, or enableDefaultTyping strings.
• File System: Evidence of file read attempts on sensitive paths (e.g., /etc/passwd, /etc/shadow, application configuration files) in OS-level audit logs; unexpected new files written by the Java application process.
• Process: Unusual child processes spawned by the Java application server (e.g., bash, sh, curl, wget); unexpected network connections initiated by the JVM process.

HubSpot has released patched versions: Jinjava 2.7.6 (for users on the 2.7.x branch) and Jinjava 2.8.3 (for users on the 2.8.x branch). Upgrading to one of these versions is the primary recommended remediation (Release 2.7.6, Release 2.8.3). As interim mitigations, restrict template creation and editing permissions to only trusted users, implement additional input validation at the application layer, and avoid rendering user-provided or untrusted Jinja template content entirely where possible (GitHub Advisory).

The vulnerability received coverage from security news outlets including SecurityOnline.info, which highlighted the critical CVSS 9.8 score and RCE potential (SecurityOnline). The Hacker Wire published a technical write-up on the arbitrary Java execution bypass (The Hacker Wire). A detailed patch-diff analysis was published by Undercode Testing, demonstrating how reversing the patch led to discovery of a pre-auth file read primitive (Undercode Testing). Community discussion was noted on Bluesky social media, and the vulnerability was included in CISA's weekly vulnerability bulletin for the week of February 2, 2026 (CISA Bulletin).