CVE-2025-55621

Executive Summary

CVE-2025-55621 is a disputed Insecure Direct Object Reference (IDOR) vulnerability in Reolink firmware version v4.54.0.4.20250526. The vulnerability allows unauthorized attackers to access and download other users' profile photos by manipulating a URL parameter. The vendor (Reolink) disputes this as intentional behavior, claiming the photos are part of a social platform where users expect to find one another. However, from a security perspective, the lack of proper authorization checks on direct object references constitutes a security flaw that could lead to privacy violations and data exposure.

Supply Chain & Package Security

This vulnerability is not related to any NPM, PyPI, Go, or Ruby package. It is a firmware-level issue in Reolink's embedded system.

CVSS Breakdown & Threat Level

• CVSS Score: 0.0 (Disputed, no official vector)
• Attack Vector: Network (AV:N)
• Attack Complexity: Low (AC:L)
• Privileges Required: None (PR:N)
• User Interaction: None (UI:N)
• Scope: Unchanged (S:U)
• Confidentiality Impact: High (C:H) – unauthorized access to profile photos
• Integrity Impact: None (I:N)
• Availability Impact: None (A:N)
• Threat Level: Medium (due to disputed status but real privacy risk)

Deep Dive & Mechanics

The vulnerability is an Insecure Direct Object Reference (IDOR) in Reolink's social platform feature. The application exposes user profile photos via URLs that contain predictable or enumerable object identifiers (e.g., user IDs or photo IDs). An attacker can craft a URL by changing the identifier to access another user's profile photo without proper authorization checks.

Root Cause: The application fails to verify that the requesting user has permission to access the specific resource (profile photo). The object reference (e.g., /photos/12345) is directly used to fetch the resource without an access control layer.

Attack Vector: An attacker can enumerate user IDs or photo IDs (e.g., sequential numbers) and send GET requests to the vulnerable endpoint. The server returns the profile photo without validating the requester's identity or relationship to the target user.

Impact: Unauthorized access to private profile photos, leading to privacy violations, potential stalking, or identity theft.

Vulnerable vs. Patched Code

Vulnerable Code (Conceptual):

@app.route('/photos/<photo_id>')
def get_photo(photo_id):
    # No authorization check
    photo = Photo.query.get(photo_id)
    return send_file(photo.path)

Patched Code (Conceptual):

@app.route('/photos/<photo_id>')
def get_photo(photo_id):
    # Authorization check
    photo = Photo.query.get(photo_id)
    if not photo.is_public and current_user.id != photo.owner_id:
        abort(403)
    return send_file(photo.path)

Note: Since the vendor disputes this as intentional, no official patch is available. The above is a recommended fix.

Exploitation & Lab Setup

Red Team

Lab Setup:

1. Deploy a Reolink device with firmware v4.54.0.4.20250526.
2. Create two user accounts (UserA and UserB) with profile photos.
3. Log in as UserA and obtain a valid session token.

Exploitation Steps:

1. Intercept a request to view UserA's profile photo (e.g., https://reolink-device/photos/12345).
2. Modify the photo ID to another user's ID (e.g., 12346).
3. Send the request without any additional authorization headers.
4. Observe that the server returns UserB's profile photo.

Proof of Concept (Python):

import requests

target_url = "https://reolink-device/photos/12346"
response = requests.get(target_url)
if response.status_code == 200:
    with open("stolen_photo.jpg", "wb") as f:
        f.write(response.content)
    print("Photo stolen successfully")
else:
    print("Failed to access photo")

Blue Team

Detection Steps:

1. Monitor for unusual patterns in photo access logs (e.g., rapid enumeration of photo IDs).
2. Implement rate limiting on photo endpoints.
3. Add authorization checks to all resource access endpoints.
4. Use Web Application Firewall (WAF) rules to block suspicious URL patterns.

Hunting Query (Splunk):

index=web_logs source="/photos/*"
| stats count by src_ip, uri
| where count > 10
| table src_ip, uri, count

Indicators of Compromise (IOCs)

• URL Pattern: /photos/[0-9]+ (sequential numeric IDs)
• HTTP Requests: GET requests to /photos/ with varying numeric IDs in short timeframes
• Response Size: Large image files (profile photos) returned without proper authentication
• Source IPs: Multiple requests from same IP to different photo IDs

Detection Engineering

YARA Rule

rule Reolink_IDOR_Photo_Access {
    meta:
        description = "Detects potential IDOR exploitation attempts on Reolink photo endpoints"
        author = "Valters IT"
        date = "2025-06-01"
        reference = "CVE-2025-55621"
    strings:
        $url_pattern = "/photos/" ascii wide nocase
        $sequential = /\/photos\/\d{4,}/ ascii wide
    condition:
        $url_pattern and #sequential > 5
}

Sigma Rule

title: Reolink IDOR Photo Enumeration
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects rapid enumeration of photo IDs on Reolink devices
author: Valters IT
date: 2025-06-01
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-uri-stem|startswith: '/photos/'
        cs-uri-stem|re: '\/photos\/\d+'
    condition: selection | count() by src_ip > 10 within 60s
falsepositives:
    - Legitimate photo browsing
level: medium

Suricata Rule

alert http any any -> any any (msg:"Reolink IDOR Photo Enumeration Attempt"; flow:to_server; content:"GET"; http_method; content:"/photos/"; http_uri; pcre:"/\/photos\/\d{4,}/"; threshold: type both, track by_src, count 10, seconds 60; sid:1000001; rev:1;)

Remediation & Mitigation

1. Immediate Action: Implement proper authorization checks on all photo access endpoints. Verify that the requesting user has permission to view the specific photo.
2. Short-term: Use non-predictable identifiers (e.g., UUIDs) for photo IDs to prevent enumeration.
3. Long-term: Conduct a full security audit of the social platform feature. Implement role-based access control (RBAC) and enforce the principle of least privilege.
4. Workaround: If the vendor does not provide a patch, consider disabling the social platform feature or restricting access to authenticated users only.
5. Monitoring: Deploy the detection rules above to identify and block exploitation attempts.

Valters IT
Securing Digital Frontiers