CVE-2019-18952 – CVE-2019-18952 allows unauthenticated attackers... (How to Fix)

Q: What is the severity of CVE-2019-18952?

CVE-2019-18952 has a CVSS score of 9.8 (CRITICAL). CVE-2019-18952 allows unauthenticated attackers to upload arbitrary files to SibSoft Xfilesharing servers via the cgi-bin/up.cgi endpoint. When combined with CVE-2019-18951 (local file inclusion), this enables remote code execution by uploading malicious HTML files containing short codes. All SibSoft Xfilesharing installations through version 2.5.1 are affected.

📋 TL;DR

CVE-2019-18952 allows unauthenticated attackers to upload arbitrary files to SibSoft Xfilesharing servers via the cgi-bin/up.cgi endpoint. When combined with CVE-2019-18951 (local file inclusion), this enables remote code execution by uploading malicious HTML files containing short codes. All SibSoft Xfilesharing installations through version 2.5.1 are affected.

💻 Affected Systems

Products:

SibSoft Xfilesharing

Versions: through 2.5.1

Operating Systems: All platforms running Xfilesharing

Default Config Vulnerable: ⚠️ Yes

Notes: All installations using the vulnerable up.cgi endpoint are affected regardless of configuration.

📦 What is this software?

Xfilesharing by Sibsoft

View all CVEs affecting Xfilesharing →

⚠️ Risk & Real-World Impact

🔴

Worst Case

Complete system compromise with attacker gaining full control of the server, data theft, and potential lateral movement to other systems.

🟠

Likely Case

Remote code execution leading to web shell installation, data exfiltration, and server takeover.

🟢

If Mitigated

File upload attempts blocked at WAF or network perimeter, limiting impact to failed exploitation attempts.

🌐 Internet-Facing: HIGH - Unauthenticated exploit allows remote attackers to compromise exposed servers.

🏢 Internal Only: MEDIUM - Internal attackers or compromised internal systems could exploit this vulnerability.

🎯 Exploit Status

Public PoC: ⚠️ Yes

Weaponized: CONFIRMED

Unauthenticated Exploit: ⚠️ Yes

Complexity: LOW

Exploit code is publicly available and requires minimal technical skill to execute.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: Version after 2.5.1

Vendor Advisory: Not available - vendor appears to be unresponsive

Restart Required: No

Instructions:

1. Upgrade to the latest version of Xfilesharing if available. 2. If no official patch exists, consider migrating to alternative software. 3. Apply workarounds listed below.

🔧 Temporary Workarounds

Block up.cgi endpoint

all

Prevent access to the vulnerable cgi-bin/up.cgi endpoint

# Apache: RewriteRule ^cgi-bin/up\.cgi$ - [F]
# Nginx: location ~ ^/cgi-bin/up\.cgi$ { return 403; }

Restrict file upload extensions

all

Configure web server to block upload of HTML and executable files

# Apache: <FilesMatch "\.(html|htm|php|exe|sh)$">
    Require all denied
</FilesMatch>
# Nginx: location ~* \.(html|htm|php|exe|sh)$ {
    deny all;
}

🧯 If You Can't Patch

Implement strict WAF rules to block requests to cgi-bin/up.cgi and suspicious file upload patterns
Isolate the Xfilesharing server in a DMZ with strict outbound firewall rules to limit damage if compromised

🔍 How to Verify

Check if Vulnerable:

Check if cgi-bin/up.cgi endpoint exists and accepts file uploads without authentication. Test by attempting to upload a test file.

Check Version:

Check Xfilesharing configuration files or admin panel for version information. Typically in config files or footer of web pages.

Verify Fix Applied:

Verify up.cgi endpoint is no longer accessible or properly validates file uploads. Test that file upload restrictions are working.

📡 Detection & Monitoring

Log Indicators:

POST requests to /cgi-bin/up.cgi with file uploads
Multiple failed upload attempts followed by successful upload
Access to unusual file extensions in web directories

Network Indicators:

Unusual outbound connections from web server
HTTP requests to known malicious domains from server IP

SIEM Query:

source="web_server" AND (uri="/cgi-bin/up.cgi" OR uri="/cgi-bin/up.cgi*") AND method="POST"

📊 Metadata

CVE ID: CVE-2019-18952

CVSS v3 Score: 9.8 (CRITICAL)

CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

CWE: CWE-434

Published: November 13, 2019

Last Updated: November 21, 2024

🔗 References

http://packetstormsecurity.com/files/155324/Xfilesharing-2.5.1-Local-File-Inclusion-Shell-Upload.html Exploit,Issue Tracking,Third Party Advisory
https://gist.github.com/pak0s/af9f640170aed335fdf6d110d468dbce Exploit,Third Party Advisory
http://packetstormsecurity.com/files/155324/Xfilesharing-2.5.1-Local-File-Inclusion-Shell-Upload.html Exploit,Issue Tracking,Third Party Advisory
https://gist.github.com/pak0s/af9f640170aed335fdf6d110d468dbce Exploit,Third Party Advisory

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