CVE-2026-4408

A flaw was found in Samba. A remote attacker can exploit a misconfiguration in Samba file servers and classic domain controllers that use the "check password script" feature. If this script is configured with the %u substitution character, the client-controlled username is passed without proper escaping of shell meta-characters. This vulnerability allows an attacker to achieve remote command execution on the affected system. This issue primarily affects non-standard configurations where the "check password script" is used with %u and the samba-dcerpcd service is started as a system service.

An Important remote code execution flaw exists in Samba file servers and classic domain controllers when configured with a 'check password script' that uses the unescaped '%u' substitution character. This vulnerability arises from a non-default configuration where the samba-dcerpcd service is started as a system service, allowing an attacker to execute arbitrary commands by injecting shell meta-characters into the username. Active Directory Domain Controllers are not affected.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.

Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base, or stability.