Description

A critical authentication bypass vulnerability in pgAdmin 4 allows unauthenticated remote attackers to impersonate arbitrary users, including administrators, by supplying a malicious HTTP identity header. Tracked as CVE-2026-86863, the flaw affects pgAdmin 4 versions 6.2 through 9.17 when Webserver authentication is enabled. The vulnerability carries a CVSS 3.1 score of 9.8 and can provide unauthorized access to privileged pgAdmin sessions. The issue exists in pgAdmin's Webserver authentication implementation, which can fall back from the trusted WEBSERVER REMOTE USER environment value to an identity supplied through an HTTP request header. Because request headers can be controlled by a remote attacker, a crafted identity value can allow authentication as an existing account without a password, MFA, or other valid credentials. Successful exploitation may provide access to database objects and data available to the impersonated account, including administrator-level resources. The vulnerability specifically affects deployments using the Webserver authentication source. Organizations should upgrade affected pgAdmin installations to version 9.18 or the latest patched release and review reverse-proxy authentication configurations. Identity headers should only be accepted from explicitly trusted proxy infrastructure. Security teams should also investigate logs for suspicious administrator sessions, unexpected identity headers, and unauthorized database activity. The patched release separates genuine CGI/WSGI identity variables from header-derived values and introduces additional controls for trusted proxies and shared-secret validation.