cPanel’s authentication bypass bug is being exploited in the wild, CISA warns

Source Domain: cyberscoop.com

A severe authentication bypass vulnerability in cPanel, one of the most widely deployed web hosting control panel platforms on the internet, is being actively exploited in the wild, according to security researchers and hosting providers.

The vulnerability, tracked as CVE-2026-41940, affects all supported versions of cPanel and WebHost Manager (WHM) released after version 11.40, as well as WP Squared, a WordPress hosting management panel built on the cPanel platform. Internet scans conducted by security firm Rapid7 using the Shodan search engine identified approximately 1.5 million cPanel instances exposed online, though the precise number of vulnerable systems remains unknown.

cPanel released a patch Tuesday. By that point, exploitation had already been underway. KnownHost, a hosting provider that relies on cPanel, said earlier this week that successful exploits had been observed in the wild prior to any fix being made available.

The Cybersecurity and Infrastructure Security Agency added the CVE to its Known Exploited Vulnerabilities (KEV) list Thursday.

Cybersecurity firm watchTowr provided technical details in a blog posted Wednesday: The flaw stems from improper handling of user input during the login process. When a user attempts to log in, cPanel writes data from the request into a server-side session file before verifying the user’s identity. An attacker can exploit this by embedding hidden line breaks into the password field of a login request — characters cPanel fails to strip out — allowing arbitrary data to be injected directly into that file.

Through a secondary step, also involving a deliberately malformed request, the injected data gets promoted into the session’s active cache, where cPanel reads it as legitimate. Once that happens, the system sees the session as already authenticated and skips password verification entirely, granting access without ever checking the user’s actual credentials.

cPanel has…

Source