CVSS 9.0 · CRITICAL

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.

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Analysis

A critical RCE vulnerability in Samba allows attackers to execute arbitrary shell commands via specially crafted usernames. This affects servers using the 'check password script' feature with the %u substitution. Admins should audit their smb.conf files and update immediately.

Relevant roles

BackendLinuxCyberSecurityWindowsCloud

Severity

Score: 9.0(CRITICAL)

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

AV: NETWORK

AC: HIGH

PR: NONE

UI: NONE

S: CHANGED

C: HIGH

I: HIGH

A: HIGH

Weakness (CWE): CWE-78

EPSS

Probability of exploitation (next 30 days): 0.0250 (2.5%)

Percentile: 82.9%

EPSS: 2026-07-14

Affects

redhat:openshift_container_platformsamba:sambaredhat:enterprise_linux

Technical description

Published: 5/28/2026, 9:16:47 AM

Last modified: 7/15/2026, 2:22:40 AM

References

How to read this card

Actively exploited

KEV (Known Exploited Vulnerabilities) is CISA's catalog of CVEs confirmed as actively exploited in the real world. If a CVE is on KEV, someone is already using it in attacks.

CVSS 10.0

CVSS 10.0 — máxima severidad teórica. Explotable de forma remota, sin privilegios, con impacto total. Aún no confirmada como explotada en el mundo real, pero parchea ya.

AI-recommended

Un modelo de lenguaje revisó el CVE y consideró que afecta a software ampliamente desplegado o herramientas comunes de desarrollo. Un humano del equipo aprobó la publicación antes de que llegara aquí.

Categorías de impacto que evalúa la IA

widely_deployed_infra — kernel Linux, OpenSSL, glibc, k8s, Docker, nginx, OpenSSH.

popular_dev_tooling — Node.js, Python, Go, React, Next.js, librerías comunes de npm/pip.

common_consumer_software — Chrome, Firefox, Windows, macOS, apps móviles populares.

enterprise_saas — GitHub, GitLab, Atlassian, Salesforce, Cisco, Fortinet, Ivanti.

niche_software — CMS regionales, herramientas de hobby, librerías de poco uso.

not_relevant — firmware específico de proveedor, software descontinuado.

EPSS — EPSS (Exploit Prediction Scoring System) by FIRST.org estimates the probability that a CVE will be exploited in the next 30 days. Range is 0 to 1; very fresh CVEs typically score low until evidence accumulates.