Source: psirt@esri.com
There is a stored cross site scripting issue in Esri ArcGIS Server 11.4 and earlier on Windows and Linux that in some configurations allows a remote unauthenticated attacker to store files that contain malicious code that may execute in the context of a victim’s browser.
Esri ArcGIS Server versions 11.4 and earlier are vulnerable to a stored cross-site scripting (XSS) attack, enabling remote, unauthenticated attackers to inject malicious code into the server. This allows attackers to compromise user browsers, potentially leading to account takeover, data exfiltration, and complete system compromise. Immediate patching and security assessments are crucial to mitigate this critical vulnerability.
Step 1: Payload Creation: The attacker crafts a malicious file (e.g., an HTML file, JavaScript file, or a file containing JavaScript) containing a JavaScript payload designed to execute in a victim's browser. This payload could be designed to steal cookies, redirect users to phishing sites, or perform other malicious actions.
Step 2: File Upload: The attacker leverages a configuration vulnerability within ArcGIS Server to upload the malicious file to the server. This may involve exploiting a misconfigured file upload feature or a vulnerability in how the server handles file storage.
Step 3: File Storage: The ArcGIS Server stores the uploaded file without proper sanitization or validation of the file's contents. The server might not correctly identify the file type or validate the content.
Step 4: Victim Interaction: A legitimate user accesses a web page or resource on the ArcGIS Server that renders or displays the attacker-uploaded file. This could be a map, a report, or any other element that incorporates the malicious file.
Step 5: Payload Execution: The victim's browser executes the malicious JavaScript payload embedded within the attacker's file. The JavaScript runs in the context of the victim's browser, allowing the attacker to perform actions on behalf of the user, such as stealing credentials or modifying data.
The vulnerability stems from insufficient input validation and output encoding within ArcGIS Server's file upload and storage mechanisms. Specifically, the server fails to properly sanitize user-supplied data, allowing an attacker to upload files containing malicious JavaScript code. When a legitimate user accesses a page that renders the attacker-controlled file, the malicious JavaScript executes within the user's browser, leading to the XSS vulnerability. The root cause is likely a missing or inadequate implementation of HTML encoding or input validation on file uploads, combined with a failure to properly sanitize the file content before storage and subsequent rendering. This allows the attacker to inject arbitrary JavaScript code that is then executed in the context of the victim's browser. The server's lack of proper content security policy (CSP) further exacerbates the issue, making it easier for the attacker's JavaScript to execute.
While no specific APTs are definitively linked at this time, the nature of the vulnerability makes it attractive to a wide range of threat actors. Nation-state actors, financially motivated groups, and script kiddies could all leverage this vulnerability. The vulnerability's potential for data exfiltration and system compromise makes it a high-value target. CISA KEV status is likely to be high or critical once the vulnerability is fully understood and exploited.
Network traffic analysis: Examine HTTP requests and responses for suspicious file uploads, especially those with unusual file extensions or content. Look for requests to potentially vulnerable endpoints within ArcGIS Server.
Web server logs: Monitor web server logs for unusual file upload activity, including the creation of new files or modifications to existing files. Analyze logs for requests containing potentially malicious JavaScript code.
File system monitoring: Monitor the file system for the creation of new files in unexpected locations or with unusual names. Look for files that contain JavaScript code or other potentially malicious content.
Intrusion detection/prevention systems (IDS/IPS): Deploy IDS/IPS rules to detect attempts to upload malicious files or exploit XSS vulnerabilities. These rules should be tailored to the specific characteristics of the ArcGIS Server environment.
Endpoint detection and response (EDR): Implement EDR solutions on endpoints to detect and respond to malicious JavaScript execution or other suspicious activity related to the XSS vulnerability.
Patching: Immediately apply the security updates provided by Esri to address the vulnerability. This is the most critical step.
Input validation: Implement robust input validation to sanitize all user-supplied data before storing it on the server. This includes validating file types, file sizes, and file content.
Output encoding: Implement proper output encoding to prevent XSS attacks. This involves encoding all user-supplied data before it is displayed in the browser.
Content Security Policy (CSP): Implement a strong CSP to restrict the sources from which the browser can load resources, such as JavaScript and CSS. This can help to mitigate the impact of XSS attacks.
Web Application Firewall (WAF): Deploy a WAF to filter malicious traffic and prevent XSS attacks. The WAF should be configured to detect and block attempts to upload malicious files or exploit XSS vulnerabilities.
Regular security assessments: Conduct regular security assessments, including penetration testing and vulnerability scanning, to identify and address security vulnerabilities.
Least privilege: Ensure that users and applications have only the necessary permissions to perform their tasks. This can help to limit the impact of a successful attack.