CVE-2021-42650 in Portainer
Summary
by MITRE • 10/19/2021
Cross Site Scripting (XSS vulnerability exists in Portainer before 2.9.1 via the node input box in Custom Templates.
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Analysis
by VulDB Data Team • 10/22/2021
The vulnerability CVE-2021-42650 represents a cross site scripting flaw discovered in Portainer versions prior to 2.9.1, specifically affecting the node input box functionality within Custom Templates. This issue stems from inadequate input validation and output encoding mechanisms that fail to properly sanitize user-supplied data before rendering it in web interfaces. The vulnerability allows malicious actors to inject malicious scripts into the application's user interface through the custom template node input field, creating potential attack vectors for session hijacking, data exfiltration, and unauthorized access to containerized environments. The flaw manifests when administrators or users create custom templates that include unvalidated node input parameters, which are then rendered without proper sanitization, enabling attackers to execute arbitrary JavaScript code in the context of other users' sessions.
The technical implementation of this vulnerability aligns with CWE-79 which defines cross site scripting as a weakness where web applications fail to properly validate or encode user-controllable data before including it in output that is sent to web browsers. This particular flaw occurs in the custom template processing pipeline where input from node configuration fields is directly incorporated into dynamic web content without appropriate security measures. The vulnerability is particularly concerning in container management environments where Portainer serves as a web-based management interface for docker containers, as it can be exploited to gain unauthorized access to critical infrastructure components. Attackers can leverage this vulnerability by crafting malicious input strings that contain script tags or other malicious payloads, which when processed through the custom template functionality, execute in the victim's browser context.
The operational impact of CVE-2021-42650 extends beyond simple script execution, as it can enable attackers to perform session manipulation, steal sensitive credentials, and potentially escalate privileges within the container management environment. In enterprise settings where Portainer is used to manage multiple containerized applications, this vulnerability could allow an attacker to gain access to the underlying docker daemon, potentially leading to complete system compromise. The vulnerability affects organizations that utilize custom templates for deploying containerized applications, making it particularly dangerous in environments where administrators frequently create and modify template configurations. The attack surface is broadened by the fact that the vulnerability exists in the administrative interface, meaning that even authenticated users could be exploited, and the impact could range from data theft to complete system takeover depending on the privileges of the compromised user.
Organizations should immediately upgrade to Portainer version 2.9.1 or later to address this vulnerability, as the fix includes proper input validation and output encoding mechanisms that prevent malicious script injection. Additional mitigations include implementing strict input validation policies for custom template creation, restricting administrative privileges to trusted users only, and monitoring for suspicious template modifications. Security teams should also consider implementing web application firewalls to detect and block potential XSS payloads, and conduct regular security assessments of container management interfaces. The vulnerability demonstrates the critical importance of input sanitization in web applications and aligns with ATT&CK technique T1059.007 which covers scripting through web shells, emphasizing the need for robust defenses against malicious code execution in containerized environments. Organizations should also implement principle of least privilege configurations and regularly audit custom template usage to prevent exploitation of similar vulnerabilities in other components of their container orchestration infrastructure.