RCE in Samba
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.
Vulnerability class: Command Injection (OS Command Injection)
Published · last modified .
CVSS v3 metric
CVSS v3 base score 9.0 (Critical). Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H.
EPSS exploit prediction
EPSS: 0.018 (77.5th percentile), scored .
Low probability of exploitation in the next 30 days, but still tracked. 77th percentile — 77.5% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.025 · newest: 0.018 · change: -0.008
Affected products
- Samba
- Red Hat Enterprise Linux 10 — versions 0:4.23.5-109.el10_2
- Red Hat Enterprise Linux 10.0 Extended Update Support — versions 0:4.21.3-114.el10_0.1
- Red Hat Enterprise Linux 6
- Red Hat Enterprise Linux 7
- Red Hat Enterprise Linux 7 Extended Lifecycle Support — versions 0:4.10.16-26.el7_9.1
- Red Hat Enterprise Linux 8 — versions 0:4.19.4-16.el8_10
- Red Hat Enterprise Linux 8.4 Advanced Mission Critical Update Support — versions 0:4.13.3-12.el8_4.1
- Red Hat Enterprise Linux 8.4 Extended Update Support Long-Life Add-On — versions 0:4.13.3-12.el8_4.1
- Red Hat Enterprise Linux 8.6 Advanced Mission Critical Update Support — versions 0:4.15.5-16.el8_6.1
Weakness classification (CWE)
Public proof-of-concept exploits
References
- access.redhat.com/security/cve/CVE-2026-4408 (Third Party Advisory, vdb-entry)
- bugzilla.redhat.com/show_bug.cgi (issue-tracking, Third Party Advisory, Issue Tracking)
- bugzilla.samba.org/show_bug.cgi (Issue Tracking, Vendor Advisory)
- access.redhat.com/errata/RHSA-2026:22644 (vendor-advisory, Issue Tracking)
- access.redhat.com/errata/RHSA-2026:22963 (vendor-advisory, Issue Tracking)
- access.redhat.com/errata/RHSA-2026:25049 (vendor-advisory)
- access.redhat.com/errata/RHSA-2026:25979 (vendor-advisory)
- access.redhat.com/errata/RHSA-2026:28057 (vendor-advisory)
- access.redhat.com/errata/RHSA-2026:28058 (vendor-advisory)
- access.redhat.com/errata/RHSA-2026:28054 (vendor-advisory)
Frequently asked questions
- What is CVE-2026-4408?
- CVE-2026-4408 is a critical-severity vulnerability in Samba, classified under OS Command Injection. CVSS score: 9.0/10. Published 2026-05-28.
- How severe is CVE-2026-4408?
- Critical severity. CVSS v3 base score is 9.0 out of 10.
- Is CVE-2026-4408 known to be exploited?
- 1 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.