CVE-2026-53523 describes an open redirect vulnerability (CWE-601) in Nezha Monitoring, a self-hostable monitoring tool. The vulnerability exists in the getRedirectURL function within oauth2.go (lines 22-29), where the OAuth2 callback URL is constructed by concatenating the request's Host header with a fixed path without validating the Host header. This lack of validation enables host header injection, allowing attackers to redirect users to arbitrary external URLs. The vulnerability affects versions from 1.0.0 up to but not including 2.2.0 and has been patched in version 2.2.0.

Successful exploitation can lead to users being redirected to malicious external sites, potentially facilitating phishing or other social engineering attacks. The CVSS 3.1 score is 6.8 (medium severity) reflecting network attack vector, high impact on confidentiality and integrity, but requiring user interaction and high attack complexity.

Upgrade Nezha Monitoring to version 2.2.0 or later, where the vulnerability has been patched. No other official remediation or temporary fixes are documented. Patch status is confirmed by the vendor advisory stating the fix in 2.2.0.