CVE-2025-9100

Executive Summary

CVE-2025-9100 is a critical authentication bypass vulnerability in Zhenfeng13 My-Blog version 1.0.0, specifically within the /blog/comment endpoint of the Frontend Blog Article Comment Handler. The flaw allows an unauthenticated remote attacker to bypass authentication mechanisms through a capture-replay attack. By intercepting a legitimate authenticated request (e.g., a comment submission) and replaying it, the attacker can impersonate a valid user or perform actions without proper credentials. This vulnerability has been publicly disclosed with proof-of-concept (PoC) code, increasing the risk of exploitation. No official patch is currently available, and the vendor has not released a fix.

CVSS Breakdown & Threat Level

• CVSS Score: 0.0 (Base Score not provided by NVD; estimated based on vector)
• Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N
• Attack Vector (AV): Network (N) – Exploitable remotely.
• 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): Low (L) – Limited information disclosure possible.
• Integrity (I): Low (L) – Limited ability to modify data (e.g., post comments as another user).
• Availability (A): None (N) – No impact on system availability.
• Threat Level: Medium – Exploitation is straightforward but impact is limited to comment functionality.

Deep Dive & Mechanics

The vulnerability resides in the comment submission handler at /blog/comment. The application fails to implement proper anti-replay protections such as nonces, timestamps, or session-bound tokens. An attacker can:

1. Intercept a legitimate HTTP request (e.g., POST to /blog/comment with comment data and a session cookie).
2. Capture the raw request using a proxy like Burp Suite or mitmproxy.
3. Replay the exact same request (including cookies and headers) to the server.
4. The server processes the replayed request as if it were a new, valid submission, bypassing authentication.

This is a classic authentication bypass by capture-replay (CWE-294). The root cause is the lack of a unique, one-time token or timestamp validation in the comment submission flow. The application likely relies solely on session cookies for authentication, but does not check if a request has already been processed.

Vulnerable vs. Patched Code

Vulnerable Code (My-Blog 1.0.0): The comment handler likely accepts POST requests without verifying a nonce or timestamp. Example pseudocode:

@app.route('/blog/comment', methods=['POST'])
def add_comment():
    # No nonce or replay protection
    user = get_current_user()  # from session cookie
    if user:
        comment = request.form['comment']
        save_comment(user, comment)
        return "Comment added"
    else:
        return "Unauthorized", 401

Patched Code (Hypothetical): A patched version would include a nonce or timestamp check:

@app.route('/blog/comment', methods=['POST'])
def add_comment():
    user = get_current_user()
    if not user:
        return "Unauthorized", 401
    nonce = request.form.get('nonce')
    if not nonce or nonce in used_nonces:
        return "Replay detected", 403
    used_nonces.add(nonce)
    comment = request.form['comment']
    save_comment(user, comment)
    return "Comment added"

Exploitation & Lab Setup

Red Team (Offensive)

Prerequisites:

• Target running My-Blog 1.0.0
• Network access to the target
• Burp Suite or similar proxy

Steps:

1. Intercept a legitimate comment submission:

   • Log in as a valid user (or find a session cookie).
   • Submit a comment via the web interface.
   • Capture the POST request to /blog/comment in Burp Suite.

2. Replay the request:

   • Send the captured request to Repeater.
   • Click "Send" multiple times.
   • Observe that each replay is accepted, creating duplicate comments.

Proof-of-Concept (Python):

import requests

target_url = "http://target/blog/comment"
session_cookie = {"session": "valid_session_cookie_here"}
data = {"comment": "Replayed comment"}

# First request (legitimate)
r = requests.post(target_url, cookies=session_cookie, data=data)
print("First request:", r.status_code)

# Replay the same request
r2 = requests.post(target_url, cookies=session_cookie, data=data)
print("Replay request:", r2.status_code)

Blue Team (Defensive)

Detection:

• Monitor for multiple identical POST requests to /blog/comment from the same IP or session within a short time window.
• Look for duplicate comment content in the database.
• Use WAF rules to block requests without a valid nonce.

Mitigation:

• Implement a nonce or CSRF token in the comment form.
• Add a timestamp check (e.g., reject requests older than 5 minutes).
• Rate-limit comment submissions per user/IP.

Indicators of Compromise (IOCs)

• Network:
  • Multiple identical POST requests to /blog/comment with the same payload.
  • Repeated use of the same session cookie in rapid succession.
• Application Logs:
  • Duplicate comment entries with identical timestamps or content.
  • Log entries showing the same request received multiple times.
• File System:
  • No specific file-based IOCs; vulnerability is logic-based.

Detection Engineering

YARA Rule

rule CVE_2025_9100_Replay_Detection {
    meta:
        description = "Detects potential replay attack on /blog/comment endpoint"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-9100"
    strings:
        $endpoint = "/blog/comment"
        $method = "POST"
    condition:
        $endpoint and $method
}

Sigma Rule

title: CVE-2025-9100 Replay Attack Detection
id: 8a9b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d
status: experimental
description: Detects multiple identical POST requests to /blog/comment within a short time window
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: 'POST'
        cs-uri-stem: '/blog/comment'
    condition: selection | count() by src_ip, cs-uri-stem > 3 within 60 seconds
falsepositives:
    - Legitimate users submitting the same comment multiple times (rare)
level: medium

Suricata Rule

alert http any any -> any any (msg:"CVE-2025-9100 Replay Attack Attempt"; flow:to_server; content:"POST"; http_method; content:"/blog/comment"; http_uri; content:"comment="; http_client_body; threshold: type both, track by_src, count 3, seconds 60; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable the comment functionality until a patch is available.
2. Implement a Web Application Firewall (WAF) rule to block duplicate requests (e.g., based on request body hash).
3. Add a nonce or CSRF token to the comment form. Generate a unique token per session and validate it server-side.
4. Introduce rate limiting on the /blog/comment endpoint (e.g., max 5 requests per minute per IP).

Long-Term Fix:

• Upgrade to a patched version of My-Blog when available.
• Conduct a security audit of all endpoints for similar replay vulnerabilities.
• Implement standard anti-replay mechanisms (timestamps, nonces, HMAC).

Workaround:

• If source code is accessible, manually add a nonce check as shown in the patched code example.

Valters IT