CVE-2026-48707

Deferred Deferred - Pending Action

Server-Side Request Forgery in InstantCMS

Publication date: 2026-09-08

Last updated on: 2026-09-08

Assigner: GitHub, Inc.

Description

InstantCMS is a free and open source content management system. Versions prior to 2.18.2 have a Server-Side Request Forgery (SSRF) vulnerability in the file upload functionality (`system/core/uploader.php` at lines 509-532). When the "upload from URL" feature follows an HTTP redirect, the redirected target URL bypasses the private IP address blacklist check. This allows authenticated users to scan and access internal network services. Version 2.18.2 contains a fix.

CVSS Scores

EPSS Scores

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Meta Information

Published

2026-09-08

Last Modified

2026-09-08

Generated

2026-09-09

AI Q&A

2026-09-09

EPSS Evaluated

N/A

NVD

CVE-2026-48707

Affected Vendors & Products

Vendor	Product	Version / Range
instantcms	instantcms	to 2.18.2 (exc)

Helpful Resources

Exploitability

CWE

KEV

CWE ID	Description
CWE-918	The web server receives a URL or similar request from an upstream component and retrieves the contents of this URL, but it does not sufficiently ensure that the request is being sent to the expected destination.

Attack-Flow Graph

Executive Summary

This is a Server-Side Request Forgery (SSRF) vulnerability in InstantCMS versions before 2.18.2. It exists in the file upload feature where HTTP redirects bypass private IP address blacklist checks. Authenticated users can exploit this to scan and access internal network services.

Detection Guidance

Check for unusual outbound HTTP requests from your InstantCMS instance, especially those following redirects to internal IP addresses. Monitor logs for file uploads via URL with unexpected destination IPs.

Impact Analysis

An attacker with authenticated access could exploit this to interact with internal systems, potentially accessing sensitive data or services not meant to be exposed. This could lead to data breaches or unauthorized network reconnaissance.

Compliance Impact

This vulnerability could lead to unauthorized access to sensitive data, violating GDPR's data protection requirements or HIPAA's security rules for protected health information. Organizations may face compliance penalties if exploited.

Mitigation Strategies

Upgrade InstantCMS to version 2.18.2 or later. Disable the 'upload from URL' feature if not required. Restrict network access to internal services from the web server.

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