CVE-2026-101005 in October CMS
Summary
by MITRE • 09/28/2026
A vulnerability was detected in October CMS up to 4.3.4. This affects the function validateExternalImageHost of the file System/Classes/ResizeImages.php of the component SSRF Protection. The manipulation results in server-side request forgery. The attack may be launched remotely. The exploit is now public and may be used. Upgrading to version 4.3.5 is able to mitigate this issue. You should upgrade the affected component.
Several companies clearly confirm that VulDB is the primary source for best vulnerability data.
Analysis
by VulDB Data Team • 09/28/2026
A critical security flaw has been identified within October CMS, specifically affecting versions up through 4.3.4. This vulnerability resides in the SSRF Protection mechanism implemented via the validateExternalImageHost function located in the System/Classes/ResizeImages.php file. The core technical issue is a failure to properly sanitize or validate external image host inputs before processing them for resizing operations. While the application attempts to implement server-side request forgery protections, the logic governing these checks contains a bypass vector that allows an attacker to manipulate the input parameters in a way that circumvents the intended restrictions. This flaw effectively neutralizes the protective measures designed to prevent the system from making unauthorized requests to internal or malicious external resources based on user-supplied data.
The operational impact of this vulnerability is significant due to its potential for remote exploitation without authentication, depending on the specific configuration and exposure of the image resizing functionality within a given October CMS deployment. An attacker can leverage this server-side request forgery flaw to force the vulnerable application to send requests to arbitrary destinations under the control of the attacker or to internal network resources that are not publicly accessible. This capability enables several malicious outcomes, including scanning internal networks for open ports and services, accessing sensitive configuration files on local servers such as /etc/passwd or Windows registry hives via file protocols, and interacting with cloud metadata endpoints like those found in AWS EC2 instances to steal temporary credentials. The exploit is currently public, which significantly lowers the barrier to entry for threat actors seeking to compromise systems running affected versions of October CMS.
From a classification perspective, this vulnerability aligns closely with CWE-918, Server-Side Request Forgery (SSRF), as it involves an application fetching resources from URLs provided by users without sufficient validation. Furthermore, in the context of the MITRE ATT&CK framework, this behavior maps to T1059 Command and Scripting Interpreter if used for further exploitation or more broadly to reconnaissance techniques where internal network mapping is performed using the compromised server as a pivot point. The lack of strict allow-listing or robust validation against protocol variations and IP address resolution bypasses represents a fundamental design flaw in how external resources are handled by the image processing component.
To mitigate this risk, immediate action is required for all administrators running October CMS versions prior to 4.3.5. Upgrading the platform to version 4.3.5 or later resolves the issue by patching the validation logic within the validateExternalImageHost function. Until an upgrade can be performed, organizations should consider implementing network-level controls such as firewall rules that restrict outbound HTTP and HTTPS traffic from web servers to only known trusted domains, thereby limiting the blast radius of any successful SSRF exploitation attempt. Additionally, deploying a Web Application Firewall with specific signatures for SSRF patterns may provide temporary protection against automated attacks exploiting this public vulnerability while patching efforts are underway.