Nezha Monitoring Pre-Auth Path Traversal via Dashboard Prefix Confusion (CVE-2026-53519)

A severe pre-authentication path traversal vulnerability (CVE-2026-53519) has been discovered in Nezha Monitoring, affecting versions prior to 2.0.13. The flaw stems from a prefix confusion in the dashboard's NoRoute handler, where the fallbackToFrontend function incorrectly processes URLs starting with /dashboard. By exploiting strings.HasPrefix and path.Join combined with Go's http.ServeFile behavior, an unauthenticated attacker can craft a malicious URL like /dashboard../data/config.yaml to bypass intended security checks and access sensitive files outside the /admin-dist directory. This allows for the exfiltration of critical data, most notably data/config.yaml, which contains the jwt_secret_key, and data/sqlite.db, which holds user account information. Possession of the jwt_secret_key enables the attacker to forge administrative JSON Web Tokens (JWTs), leading to full administrative account takeover of the Nezha Monitoring instance.

Attack Chain

1. An unauthenticated attacker sends an HTTP GET request to a crafted URL like /dashboard../data/config.yaml, targeting the Nezha Monitoring dashboard.
2. The vulnerable fallbackToFrontend handler's strings.HasPrefix check incorrectly matches /dashboard.., and strings.TrimPrefix leaves ../data/config.yaml.
3. path.Join("admin-dist", "../data/config.yaml") normalizes the path to data/config.yaml, causing os.Stat to locate the sensitive file.
4. Go's http.ServeFile serves the data/config.yaml file to the attacker, bypassing its internal ..-segment guard due to the non-canonical /dashboard.. segment.
5. The attacker extracts the jwt_secret_key from the exfiltrated config.yaml and repeats the process to exfiltrate data/sqlite.db, identifying administrative user IDs.
6. Using the jwt_secret_key and an administrative user ID, the attacker forges a valid HS256-signed JWT for an administrator account.
7. The attacker uses the forged JWT as a session cookie or Bearer token to gain full administrative access to the Nezha Monitoring dashboard, enabling actions like server management, user creation/deletion, and notification configuration.

Impact

Successful exploitation of CVE-2026-53519 grants an unauthenticated attacker the ability to read any file within the dashboard's working directory subtree, provided it is one level up from admin-dist. In default deployments, this includes data/config.yaml, which contains sensitive secrets such as the jwt_secret_key, agent_secret_key, OAuth2 client secrets, and GeoIP API keys. Additionally, data/sqlite.db can be exfiltrated, revealing the full dashboard state including all users (and their bcrypt password hashes), server registries, and API tokens. The primary impact is immediate administrative account takeover, allowing the attacker to fully control the Nezha Monitoring instance, potentially leading to data manipulation, unauthorized monitoring, or further compromise of integrated systems.

Recommendation

• Immediately update Nezha Monitoring to version 2.0.13 or newer to patch CVE-2026-53519.
• Deploy the provided Sigma rule to your SIEM to detect and alert on attempts to exploit CVE-2026-53519.
• Implement Web Application Firewall (WAF) rules to block HTTP GET requests containing the /dashboard../data/config.yaml and /dashboard../data/sqlite.db patterns, including their URL-encoded variants listed in the IOCs.
• Review access logs for the IOC URLs prior to patching to identify potential exploitation attempts.