CVE-2026-55807

Executive Summary

CVE-2026-55807 is a critical Server-Side Request Forgery (SSRF) vulnerability affecting Drupal core across multiple version branches. This flaw allows an unauthenticated attacker to make the Drupal server send crafted requests to internal or external systems, potentially leading to information disclosure, internal network reconnaissance, or further exploitation. The vulnerability impacts all Drupal installations from version 0.0.0 up to 10.5.12, 10.6.0 to 10.6.11, 11.2.0 to 11.2.14, 11.3.0 to 11.3.12, and all 11.0.x and 11.1.x releases. No official patch or exploit code has been published at this time, but the risk is significant due to the widespread use of Drupal.

Supply Chain & Package Security

Drupal is a PHP-based content management framework distributed via its own package ecosystem (Drupal.org) and Composer. This vulnerability affects the core package, meaning any site using a vulnerable version is at risk. Organizations should verify their Drupal version and apply any available security updates immediately. The lack of a patch at this time necessitates enhanced monitoring and mitigation controls.

CVSS Breakdown & Threat Level

While no official CVSS vector has been assigned, based on the nature of SSRF vulnerabilities in similar CMS platforms, the following is a reasonable estimate:

• 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) – The vulnerable component is the only one affected.
• Confidentiality (C): High (H) – Potential to read internal resources.
• Integrity (I): Low (L) – Limited ability to modify data.
• Availability (A): None (N) – No direct impact on availability.

Estimated CVSS Score: 8.6 (High)

Threat Level: High. The vulnerability is remotely exploitable without authentication, and SSRF can lead to severe internal network compromise.

Deep Dive & Mechanics

The vulnerability resides in Drupal's core HTTP request handling, likely within the Drupal\Component\Utility\UrlHelper or similar URL processing components. The SSRF occurs when the application processes user-supplied URLs without proper validation or restriction on the target host or scheme.

Root Cause: The application fails to validate that the target URL of an outgoing request is not an internal or private IP address (e.g., 127.0.0.1, 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16, or [::1]). An attacker can craft a request that forces the server to make a request to an internal service, such as a database, caching layer, or cloud metadata endpoint.

Attack Vector: The attacker sends a specially crafted HTTP request to a Drupal endpoint that triggers an outbound HTTP request. This could be through:

• A file upload or import feature that fetches a URL.
• A webhook or callback configuration.
• A proxy or redirect functionality.
• Any module that uses drupal_http_request() or \Drupal::httpClient() with user input.

Impact:

• Internal Network Scanning: The attacker can probe internal services and identify running applications.
• Cloud Metadata Access: On cloud platforms (AWS, GCP, Azure), the attacker can access instance metadata endpoints (e.g., http://169.254.169.254/latest/meta-data/) to retrieve credentials and configuration.
• Data Exfiltration: Sensitive data from internal services can be read.
• Server-Side Request Forgery to Server-Side Include (SSRF to SSI): In some cases, the attacker may be able to execute commands on internal services.

Vulnerable vs. Patched Code

Since no official patch is available, the following is a conceptual comparison based on common SSRF fixes.

Vulnerable Code (Conceptual):

// In a Drupal module or core function
function vulnerable_fetch_url($url) {
  $response = \Drupal::httpClient()->get($url);
  // Process response without validating URL
  return $response->getBody();
}

Patched Code (Conceptual):

// Patched version with URL validation
function patched_fetch_url($url) {
  // Validate URL scheme and host
  $parsed_url = parse_url($url);
  if (!in_array($parsed_url['scheme'], ['http', 'https'])) {
    throw new \InvalidArgumentException('Invalid scheme');
  }
  $host = $parsed_url['host'];
  // Resolve host to IP and check against private ranges
  $ip = gethostbyname($host);
  if (filter_var($ip, FILTER_VALIDATE_IP, FILTER_FLAG_NO_PRIV_RANGE | FILTER_FLAG_NO_RES_RANGE) === false) {
    throw new \InvalidArgumentException('Request to private IP blocked');
  }
  $response = \Drupal::httpClient()->get($url);
  return $response->getBody();
}

Exploitation & Lab Setup

Red Team

Lab Setup:

1. Deploy a vulnerable Drupal instance (e.g., version 10.5.12) using Docker:

   docker run -d -p 8080:80 --name drupal-vuln drupal:10.5.12
   

2. Set up a listener on the host to capture outbound requests:

   nc -lvnp 9999
   

3. Identify an endpoint that makes outbound HTTP requests (e.g., a webform that fetches a URL).

Exploitation Steps:

1. Craft a request to the vulnerable endpoint with a malicious URL:

   POST /webform/submit HTTP/1.1
   Host: target-drupal-site.com
   Content-Type: application/x-www-form-urlencoded
   
   url=http://169.254.169.254/latest/meta-data/iam/security-credentials/admin
   

2. Observe the server making a request to the internal metadata endpoint.
3. Retrieve sensitive data (e.g., AWS credentials) from the response.

Alternative Payloads:

• http://127.0.0.1:6379 (Redis)
• http://127.0.0.1:3306 (MySQL)
• http://127.0.0.1:11211 (Memcached)
• file:///etc/passwd (if file scheme is allowed)

Blue Team

Detection:

• Monitor outbound HTTP requests from the Drupal server to private IP ranges.
• Look for requests to 169.254.169.254 or other cloud metadata endpoints.
• Analyze server logs for unusual URL parameters containing IP addresses or internal hostnames.

Mitigation:

• Implement a Web Application Firewall (WAF) rule to block requests containing private IP addresses.
• Use network segmentation to restrict outbound traffic from the web server.
• Apply virtual patching by modifying the Drupal code to validate URLs (see patched code above).
• Disable unnecessary features that make outbound HTTP requests.

Indicators of Compromise (IOCs)

• Network IOCs:
  • Outbound HTTP requests to private IP ranges (10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16, 127.0.0.0/8, [::1]).
  • Requests to cloud metadata endpoints (169.254.169.254, 169.254.170.2).
  • Unusual User-Agent strings in outbound requests (e.g., "Drupal" or "GuzzleHttp").
• File IOCs:
  • Modified Drupal core files (e.g., core/lib/Drupal/Component/Utility/UrlHelper.php).
  • Suspicious log entries in watchdog or syslog indicating failed URL validation.
• Process IOCs:
  • PHP processes making unexpected outbound connections.
  • Elevated memory or CPU usage from repeated SSRF attempts.

Detection Engineering

YARA Rule

rule CVE_2026_55807_SSRF_Drupal {
    meta:
        description = "Detects potential SSRF exploitation attempts in Drupal logs"
        author = "Valters IT"
        date = "2026-01-01"
        reference = "CVE-2026-55807"
    strings:
        $s1 = "169.254.169.254" ascii wide nocase
        $s2 = "127.0.0.1" ascii wide nocase
        $s3 = "10." ascii wide nocase
        $s4 = "192.168." ascii wide nocase
        $s5 = "172.16." ascii wide nocase
        $s6 = "file://" ascii wide nocase
        $s7 = "gopher://" ascii wide nocase
    condition:
        any of ($s*) and filesize < 10MB
}

Sigma Rule

title: Drupal SSRF Exploitation Attempt
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects outbound HTTP requests from Drupal to private IP ranges
author: Valters IT
date: 2026-01-01
references:
    - https://nvd.nist.gov/vuln/detail/CVE-2026-55807
logsource:
    category: network_connection
    product: suricata
detection:
    selection:
        dest_ip:
            - '10.0.0.0/8'
            - '172.16.0.0/12'
            - '192.168.0.0/16'
            - '127.0.0.0/8'
            - '::1'
        dest_port: 
            - 80
            - 443
            - 8080
        app_protocol: http
    condition: selection
falsepositives:
    - Legitimate internal monitoring tools
level: high

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2026-55807 Drupal SSRF to Private IP"; flow:to_server; content:"GET"; http_method; content:"Host:"; http_header; pcre:"/Host:\s*(10\.|172\.(1[6-9]|2[0-9]|3[01])\.|192\.168\.|127\.|169\.254\.)/Ri"; classtype:attempted-recon; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Isolate vulnerable systems: Place Drupal servers behind a firewall that blocks outbound traffic to private IP ranges.
2. Disable unnecessary features: Temporarily disable any modules or features that make outbound HTTP requests based on user input.
3. Apply virtual patch: Modify the Drupal core code to validate URLs (see patched code example) or use a WAF to block SSRF attempts.

Long-term Fix:

• Monitor the Drupal security advisory page (https://www.drupal.org/security) for an official patch.
• Upgrade to a patched version once released.
• Implement a Content Security Policy (CSP) that restricts outbound connections.
• Conduct a security audit of all custom modules that use HTTP clients.

Valters IT Signature

This report was generated by Valters IT Cyber Threat Intelligence. For questions, contact threatintel@valtersit.com.