CVE-2021-23345 in Gotenberg
Summary
by MITRE • 02/26/2021
All versions of package github.com/thecodingmachine/gotenberg are vulnerable to Server-side Request Forgery (SSRF) via the /convert/html endpoint when the src attribute of an HTML element refers to an internal system file, such as .
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Analysis
by VulDB Data Team • 03/05/2021
The vulnerability identified as CVE-2021-23345 affects the github.com/thecodingmachine/gotenberg package, which is a document conversion service that processes HTML content and converts it to various formats including PDF. This package is widely used in enterprise environments for automated document generation and processing workflows. The vulnerability manifests within the /convert/html endpoint where the application fails to properly validate and sanitize file paths referenced in HTML elements, creating a critical security flaw that can be exploited by malicious actors to access internal system resources.
The technical flaw stems from inadequate input validation mechanisms within the HTML processing pipeline of the gotenberg service. When HTML content is submitted for conversion, the system attempts to resolve the src attribute of HTML elements without proper sanitization checks. This allows attackers to craft malicious HTML payloads where the src attribute points to internal system files such as /etc/passwd or other sensitive resources. The vulnerability is classified as a Server-Side Request Forgery (SSRF) as defined by CWE-918, which occurs when an application processes external input that specifies a request to a remote server without proper validation. The flaw specifically enables attackers to bypass normal network access controls and make unauthorized requests to internal services that should be restricted from external access.
The operational impact of this vulnerability is severe and multifaceted. Attackers can leverage this flaw to enumerate internal system resources, potentially gaining access to sensitive files, system information, and internal network services that are not intended to be publicly accessible. The vulnerability allows for reconnaissance activities where attackers can map internal network structures, identify running services, and extract system-level information. Additionally, the flaw can be chained with other vulnerabilities to escalate privileges or gain unauthorized access to internal databases and services. This type of vulnerability falls under the ATT&CK technique T1071.004 for Application Layer Protocol: DNS, as the SSRF can be used to make DNS requests to internal systems that are not directly accessible from the internet.
Mitigation strategies for this vulnerability require immediate implementation of input validation and sanitization mechanisms. Organizations should ensure that all file path references in HTML elements are properly validated against a whitelist of allowed protocols and domains. The gotenberg package should be updated to version 7.2.0 or later where this vulnerability has been patched through enhanced input validation. Network segmentation and firewall rules should be implemented to restrict access to internal services, while implementing proper access controls to limit the scope of potential damage. Security monitoring should be enhanced to detect unusual patterns in document conversion requests that may indicate exploitation attempts. Organizations should also implement principle of least privilege for the gotenberg service, limiting its access to only necessary internal resources and employing proper logging mechanisms to track all file access attempts. The vulnerability demonstrates the critical importance of validating all external inputs and implementing proper boundary checks in web applications processing user-supplied content.