CVE-2021-27693 in PublicCMS
Summary
by MITRE • 09/02/2022
Server-side Request Forgery (SSRF) vulnerability in PublicCMS before 4.0.202011.b via /publiccms/admin/ueditor when the action is catchimage.
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Analysis
by VulDB Data Team • 10/13/2022
The CVE-2021-27693 vulnerability represents a critical server-side request forgery flaw discovered in PublicCMS versions prior to 4.0.202011.b. This vulnerability specifically affects the administrative interface of the content management system, particularly when utilizing the ueditor component with the catchimage action parameter. The flaw enables attackers to manipulate the server's request handling mechanism, potentially allowing unauthorized access to internal systems or resources that should remain protected from external exposure. The vulnerability resides within the server-side processing logic that handles image capture functionality, creating an attack surface where malicious requests can be directed to internal network resources without proper authorization checks.
The technical implementation of this vulnerability stems from insufficient validation of user-supplied input parameters within the ueditor component's catchimage action handler. When administrators or authenticated users access the /publiccms/admin/ueditor endpoint with the catchimage action, the system fails to properly sanitize or validate the URL parameters that specify the source of images to be captured. This lack of input validation creates an opportunity for attackers to supply malicious URLs that point to internal systems, localhost addresses, or other restricted resources within the network. The vulnerability directly maps to CWE-918, which classifies server-side request forgery as a weakness where applications fail to properly validate or restrict external resource requests that can be manipulated by attackers. The flaw allows for arbitrary URL requests to be processed by the server, potentially enabling attackers to access internal services, databases, or other sensitive resources that are normally protected from external access.
The operational impact of this vulnerability extends beyond simple information disclosure, as it can enable attackers to perform reconnaissance activities against internal network infrastructure. An attacker could leverage this vulnerability to scan internal ports, access internal web applications, or even attempt to exploit other vulnerabilities within the internal network that are not directly exposed to the internet. The attack vector typically involves crafting specially formatted URLs that contain internal IP addresses, localhost references, or other internal resources that the server can access. This capability significantly increases the risk of privilege escalation attacks and can lead to complete system compromise if internal services are not properly secured. The vulnerability affects organizations using older versions of PublicCMS, particularly those that have not applied the security patches released in version 4.0.202011.b. The potential for exploitation aligns with ATT&CK technique T1190, which describes server-side request forgery as a method for attackers to bypass network security controls and access internal resources.
Organizations should immediately implement mitigations to address this vulnerability by upgrading to PublicCMS version 4.0.202011.b or later, which includes proper input validation and sanitization mechanisms for the ueditor component. Additional protective measures include implementing network segmentation to limit access to administrative interfaces, configuring firewalls to restrict outbound connections from the CMS server, and implementing proper input validation at multiple layers of the application architecture. Security monitoring should be enhanced to detect unusual patterns in URL requests to the ueditor component, particularly those containing localhost or private IP address references. The remediation process should also include comprehensive code reviews of similar components within the application to identify potential similar vulnerabilities, as this flaw demonstrates a pattern of insufficient input validation in web application components. Organizations should also consider implementing web application firewalls to provide additional protection against such attacks, and conduct regular vulnerability assessments to ensure all components are properly updated and secured against known threats.