CVE-2020-8902 in Rendertron
Summary
by MITRE • 02/23/2021
Rendertron versions prior to 3.0.0 are are susceptible to a Server-Side Request Forgery (SSRF) attack. An attacker can use a specially crafted webpage to force a rendertron headless chrome process to render internal sites it has access to, and display it as a screenshot. Suggested mitigations are to upgrade your rendertron to version 3.0.0, or, if you cannot update, to secure the infrastructure to limit the headless chrome's access to your internal domain.
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Analysis
by VulDB Data Team • 03/04/2021
The vulnerability identified as CVE-2020-8902 affects Rendertron versions prior to 3.0.0 and represents a critical server-side request forgery flaw that enables attackers to manipulate the headless chrome rendering process. This issue stems from insufficient input validation and access control mechanisms within the application's architecture, allowing malicious actors to exploit the system's ability to render arbitrary web content. The vulnerability specifically targets the way Rendertron handles URL inputs during the rendering process, creating an avenue for unauthorized access to internal network resources that would normally be protected from external exposure.
The technical implementation of this vulnerability leverages the legitimate functionality of Rendertron's headless chrome browser to make unauthorized requests to internal systems. When an attacker crafts a malicious URL that includes internal network addresses or protocols, the vulnerable version of Rendertron fails to properly validate these inputs before initiating the rendering process. This allows the headless chrome instance to connect to internal resources such as localhost services, internal APIs, or other network-attached systems that should remain isolated from external access. The rendered output of these internal resources can then be captured and displayed to the attacker through the screenshot functionality, effectively exposing sensitive internal information.
The operational impact of this vulnerability extends beyond simple information disclosure, as it can enable attackers to perform reconnaissance on internal network infrastructure and potentially escalate privileges within the affected environment. The attack surface includes access to internal web applications, database interfaces, and system management tools that may be running on standard ports within the internal network. This vulnerability aligns with CWE-918, which specifically addresses server-side request forgery conditions where an attacker can manipulate a server into making requests to arbitrary destinations. The implications are particularly severe in environments where Rendertron is deployed in production systems, as it could provide attackers with detailed views of internal infrastructure and potentially expose authentication mechanisms or sensitive configuration data.
Mitigation strategies for CVE-2020-8902 should prioritize immediate version upgrading to Rendertron 3.0.0 or later, which includes comprehensive input validation and access control improvements. Organizations unable to perform immediate upgrades must implement network-level restrictions to limit the headless chrome process's ability to access internal resources. This includes implementing strict firewall rules, network segmentation, and access control lists that prevent outbound connections from the rendering service to internal network segments. The solution should also incorporate proper URL sanitization and validation at the application level, ensuring that only explicitly permitted domains or protocols are processed by the rendering engine. Additionally, organizations should consider implementing monitoring and logging mechanisms to detect anomalous requests that might indicate exploitation attempts, aligning with ATT&CK technique T1071.004 for application layer protocol usage and T1566.001 for credential access through social engineering.
The vulnerability demonstrates the critical importance of input validation in web applications that interface with external services or network resources. Rendertron's architecture, while designed for legitimate web rendering purposes, failed to implement proper access controls that would prevent abuse of its core functionality. This incident highlights the need for comprehensive security testing during application development, particularly for services that process user-supplied inputs and interact with network resources. The attack vector represents a common pattern in modern web applications where legitimate features become security risks when proper access controls are not implemented, emphasizing the principle of least privilege and defense in depth strategies. Organizations should conduct thorough security assessments of their application stacks to identify similar vulnerabilities that could be exploited through similar attack patterns.