Exploit for CVE-2026-20131

## https://sploitus.com/exploit?id=66F1292F-0D88-5668-9447-4DFC77C38D29
# CVE-2026-20131 — Cisco FMC Insecure Java Deserialization (RCE)

## Description

A vulnerability in the web-based management interface of **Cisco Secure Firewall Management Center (FMC)** Software that allows an unauthenticated, remote attacker to execute **arbitrary Java code as root** via insecure deserialization of a user-supplied Java byte stream.

- **CWE:** CWE-502 — Deserialization of Untrusted Data
- **Vendor Advisory:** [cisco-sa-fmc-rce-NKhnULJh](https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-fmc-rce-NKhnULJh)

## Root Cause

The FMC web interface deserializes user-supplied Java objects without proper validation. An attacker sends a crafted serialized Java object to trigger arbitrary code execution.

## Impact

- Unauthenticated remote code execution
- Full **root-level** access to the underlying OS
- Reduced attack surface if FMC is not internet-facing

## Affected Products

Cisco Secure Firewall Management Center (FMC) — refer to Cisco's advisory for specific affected versions.

## Detection Script

`check_cve_2026_20131.py` — sends Java serialization magic bytes (`AC ED 00 05`) to known FMC endpoints and inspects responses for signs of deserialization processing.

> **Safe probe only** — no exploit gadget chain is used. Indicators are based on HTTP response codes (500/200 on serialized input).

### Requirements

```bash
pip install requests
```

### Usage

```bash
python3 check_cve_2026_20131.py https://
```

### Output

| Result | Meaning |
|--------|---------|
| `POTENTIALLY VULNERABLE` | Endpoint processed serialized bytes (500/200 response) |
| `No obvious exposure detected` | Endpoints rejected or unreachable — likely patched |

## Remediation

Apply the patch from the official Cisco advisory:
https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-fmc-rce-NKhnULJh

**Mitigations (if patching is not immediately possible):**
- Restrict FMC management interface access to trusted IPs only
- Block public internet access to the FMC interface

## Disclaimer

> This script is intended for **authorized security testing and defensive purposes only**.
> Only run against systems you own or have **explicit written permission** to test.
> Unauthorized use may violate laws including the Computer Fraud and Abuse Act (CFAA).