CVE-2026-4408: Samba: remote code execution in samr

Severity: critical (CVSS 9.8 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 2.5% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-05-28 · updated 2026-10-26
Weakness: CWE-78

Description

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.

Affected products

Red Hat Enterprise Linux: 6.0, 7.0, 9.0
Red Hat OpenShift Container Platform 4.18: 4.0
Samba: from 4.1.0 before 4.21.0 — fixed in 4.21.0

How to fix

Upgrade to a fixed version: Samba 4.21.0. Check the vendor advisory for mitigations.

References

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