CVE-2026-0397: CORS Misconfiguration Info Disclosure Flaw

CVE-2026-0397 Overview

A Cross-Origin Resource Sharing (CORS) misconfiguration vulnerability exists in DNSdist's internal webserver component. When the internal webserver is enabled (disabled by default), an attacker may be able to trick an administrator who is logged into the dashboard into visiting a malicious website. Through this social engineering attack, the attacker can extract information about the running configuration from the dashboard.

Critical Impact

Attackers can leverage CORS misconfiguration to exfiltrate sensitive configuration data from the DNSdist dashboard when administrators are tricked into visiting malicious sites.

Affected Products

• DNSdist (versions with internal webserver enabled)

Discovery Timeline

• 2026-03-31 - CVE CVE-2026-0397 published to NVD
• 2026-04-01 - Last updated in NVD database

Technical Details for CVE-2026-0397

Vulnerability Analysis

This vulnerability is classified as CWE-942: Permissive Cross-domain Policy with Untrusted Domains. The CORS misconfiguration allows cross-origin requests from untrusted domains to access sensitive resources on the DNSdist dashboard. While the vulnerability requires user interaction (an administrator must be logged into the dashboard and visit a malicious website), successful exploitation could lead to information disclosure of the running configuration.

The attack complexity is high as it requires precise timing and social engineering to get an authenticated administrator to visit the attacker-controlled site. The impact is limited to confidentiality, with no direct effect on integrity or availability of the system.

Root Cause

The root cause of this vulnerability is a misconfiguration of the Cross-Origin Resource Sharing (CORS) policy in the DNSdist internal webserver. The CORS policy does not properly restrict which origins are permitted to make cross-origin requests to the dashboard API, allowing malicious websites to potentially read responses from authenticated sessions.

Attack Vector

The attack requires an authenticated administrator to visit a malicious website while logged into the DNSdist dashboard. The malicious website can then make cross-origin requests to the dashboard API, and due to the permissive CORS policy, the browser will allow the malicious site to read the responses. This enables the attacker to extract configuration information from the dashboard.

The vulnerability is exploited through a network-based attack vector where the attacker hosts malicious JavaScript code designed to make requests to the DNSdist dashboard endpoints. When the administrator's browser executes this code, it inadvertently sends authenticated requests to the dashboard, and the CORS misconfiguration allows the response data to be accessed by the attacker's domain.

Detection Methods for CVE-2026-0397

Indicators of Compromise

• Unusual cross-origin requests to the DNSdist dashboard from external domains
• Web server logs showing requests with unexpected Origin headers
• Browser developer console warnings about CORS policy violations from legitimate administrators may indicate testing or reconnaissance

Detection Strategies

• Monitor web server access logs for requests containing suspicious Origin headers that don't match expected administrative domains
• Implement browser security policies that alert on cross-origin resource access attempts
• Review dashboard access patterns for anomalous request sequences that may indicate data exfiltration

Monitoring Recommendations

• Enable detailed logging for the DNSdist internal webserver to capture all incoming requests with full headers
• Set up alerts for dashboard access from unexpected geographic locations or IP ranges
• Consider implementing Content Security Policy (CSP) headers to provide additional protection and monitoring capabilities

How to Mitigate CVE-2026-0397

Immediate Actions Required

• If the internal webserver is not required, ensure it remains disabled (the default configuration)
• If the webserver is enabled, restrict access to the dashboard to trusted networks only using firewall rules
• Review and update the CORS configuration to explicitly whitelist only trusted origins
• Ensure administrators are aware of the risk and avoid accessing untrusted websites while logged into the dashboard

Patch Information

PowerDNS has released a security advisory addressing this vulnerability. Organizations using DNSdist with the internal webserver enabled should review the DNSdist Security Advisory for specific patch information and updated versions. Apply the recommended patches as soon as they are available for your deployment.

Workarounds

• Disable the internal webserver if it is not required for your deployment
• Implement network-level access controls to restrict dashboard access to trusted IP addresses only
• Use a reverse proxy in front of the dashboard with properly configured CORS policies
• Advise administrators to use separate browser profiles or sessions when accessing the dashboard to isolate authentication tokens from general browsing

# Example: Restrict dashboard access to localhost only
# In dnsdist configuration, bind webserver to localhost
webserver("127.0.0.1:8083")

# Alternative: Use firewall rules to restrict access
# iptables -A INPUT -p tcp --dport 8083 -s 192.168.1.0/24 -j ACCEPT
# iptables -A INPUT -p tcp --dport 8083 -j DROP