CVE-2026-4408

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.

CVSS v3.1 Score

9.0

CRITICAL

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H

EPSS — Exploit Prediction

0.0187

Probability of exploitation

0.77%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

Weakness Type (CWE)

CWE-78 OS Command Injection

References

Other References

https://access.redhat.com/errata/RHSA-2026:22644 https://access.redhat.com/errata/RHSA-2026:22963 https://access.redhat.com/security/cve/CVE-2026-4408 https://bugzilla.redhat.com/show_bug.cgi?id=2479762 https://bugzilla.samba.org/show_bug.cgi?id=16034

Frequently Asked Questions

What is 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. It has a CVSS v3.1 base score of 9.0 (CRITICAL).

How severe is CVE-2026-4408? +

CVE-2026-4408 has a CVSS v3.1 score of 9.0 out of 10, rated CRITICAL. This is a critical vulnerability that should be patched immediately. The EPSS score is 0.0187, placing it in the 1th percentile for exploitation probability.

How do I check if I'm vulnerable to CVE-2026-4408? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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