New WAF Rule for JinJava Sandbox Bypass (CVE-2025-59340)
Cloudflare deployed a new WAF rule to block CVE-2025-59340, a JinJava template engine sandbox bypass that could allow attackers to execute arbitrary code through unsafe template rendering. The rule now blocks this vulnerability by default instead of just logging attempts.
This week’s highlights include a new JinJava rule targeting a sandbox-bypass flaw that could allow malicious template input to escape execution controls. The rule improves detection for unsafe template rendering paths.
Key Findings
New WAF rule deployed for JinJava (CVE-2025-59340) to block a sandbox bypass in the template engine that permits attacker-controlled type construction and arbitrary class instantiation; in vulnerable environments this can escalate to remote code execution and full server compromise.
Impact
- CVE-2025-59340 — Exploitation enables attacker-supplied type descriptors / Jackson
ObjectMapperabuse, allowing arbitrary class loading, file/URL access (LFI/SSRF primitives) and, with suitable gadget chains, potential remote code execution and system compromise.
| Ruleset | Rule ID | Legacy Rule ID | Description | Previous Action | New Action | Comments |
|---|---|---|---|---|---|---|
| Cloudflare Managed Ruleset | ...c04bab5f | 100892 | JinJava - SSTI - CVE:CVE-2025-59340 | Log | Block | This is a New Detection |
Source: original entry ↗
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