CVE-2026-56661 in GetSimple CMS
Summary
by MITRE • 10/01/2026
GetSimple CMS is a content management system (CMS), and GetSimple CMS CE is the community edition of that CMS. Prior to version 1.5, the update handler fetches a user-supplied URL with file_get_contents() after only format validation (FILTER_VALIDATE_URL) — there is no validation of the request destination. An attacker who can submit the form can make the server issue requests to arbitrary destinations, including internal-only services and cloud metadata endpoints (169.254.169.254). The fetched response body is written to a web-accessible file (/Tmpfile.zip) and is not deleted when the content is not a valid ZIP, turning this into a full-read SSRF: the attacker can retrieve the response of the internal request directly. This issue has been patched in version 1.5.
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Analysis
by VulDB Data Team • 10/01/2026
The vulnerability identified in GetSimple CMS versions prior to 1.5 represents a critical Server-Side Request Forgery (SSRF) flaw rooted in insufficient input validation within the platform's update handler mechanism. As an open-source content management system, GetSimple allows administrators and potentially other authenticated users to manage site updates through web-based forms. The core technical failure lies in how the application processes user-supplied URLs intended for fetching remote resources. Specifically, the software utilizes PHP’s file_get_contents function to retrieve data from a URL provided by the user. While the implementation includes a basic format check using FILTER_VALIDATE_URL, this validation is superficial as it only ensures that the string conforms to standard URI syntax rules such as having a valid scheme and host structure. It does not perform any semantic or destination-based verification to ensure the target address belongs to an allowed list of external domains or excludes internal network ranges. This lack of strict allowlisting or blocklist enforcement against private IP addresses, loopback interfaces, and cloud metadata endpoints creates a significant security gap that can be exploited by attackers with access to the update form interface.
The operational impact of this vulnerability is severe due to its ability to facilitate full-read SSRF attacks. By submitting a crafted URL pointing to internal services or sensitive infrastructure components, an attacker can force the server to initiate HTTP requests on their behalf. A particularly dangerous aspect of this flaw involves cloud metadata endpoints, such as 169.254.169.254 commonly found in Amazon Web Services and other cloud environments. These endpoints often contain temporary security credentials, instance identity documents, and configuration data that are not authenticated by default but are accessible to any process running on the instance. If an attacker can direct the server to query these endpoints, they may retrieve sensitive authentication tokens or system configurations, potentially leading to complete compromise of the underlying cloud infrastructure. Furthermore, the vulnerability extends beyond simple request initiation because of how the application handles the response data. The fetched content is written directly to a web-accessible file named /Tmpfile.zip within the public directory structure. Crucially, this file is not deleted if the downloaded content fails validation as a valid ZIP archive. This behavior transforms what might otherwise be a blind SSRF into a full-read vulnerability, allowing the attacker to retrieve arbitrary data from internal services by simply accessing the resulting file through their web browser or automated tools.
From a classification perspective, this issue aligns with CWE-918 Server-Side Request Forgery (SSRF), specifically highlighting weaknesses in input validation and destination control mechanisms. The exploitation technique maps directly to MITRE ATT&CK techniques related to Discovery and Credential Access, particularly T1046 Network Service Scanning for internal reconnaissance and T1552 Unsecured Credentials if cloud metadata is accessed. The failure to validate the actual network destination despite validating the format of the input string illustrates a common pattern where developers assume syntactic correctness implies semantic safety. This oversight allows attackers to bypass basic filters by using standard URL formats that point to restricted resources, demonstrating the necessity for robust server-side validation strategies that include IP address resolution checks and domain allowlisting before initiating any network connections.
Mitigation of this vulnerability requires immediate action on multiple fronts. The primary remediation is upgrading GetSimple CMS to version 1.5 or later, where the developers have addressed these flaws by implementing stricter destination validation logic. For environments unable to upgrade immediately, defensive measures should include configuring web servers and application firewalls to block outbound requests to private IP ranges such as 10.x.x.x, 172.16-31.x.x, 192.168.x.x, and the cloud metadata address 169.254.169.254. Additionally, implementing network-level egress filtering can prevent compromised servers from communicating with unauthorized internal services or external malicious endpoints. Application-layer defenses should also enforce strict allowlists for permitted update sources rather than relying on negative filters that only block known bad actors. Regular security audits of CMS plugins and core components are essential to identify similar patterns where user input is directly passed to network functions without adequate destination verification, ensuring the integrity and confidentiality of both the application data and the underlying infrastructure it resides upon.