CVE-2026-4408
Publication date 26 May 2026
Last updated 10 June 2026
Ubuntu priority
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.
Status
| Package | Ubuntu Release | Status |
|---|---|---|
| samba | 26.04 LTS resolute |
Fixed 2:4.23.6+dfsg-1ubuntu2.1
|
| 25.10 questing |
Fixed 2:4.22.3+dfsg-4ubuntu2.4
|
|
| 24.04 LTS noble |
Fixed 2:4.19.5+dfsg-4ubuntu9.6
|
|
| 22.04 LTS jammy |
Fixed 2:4.15.13+dfsg-0ubuntu1.12
|
|
| 20.04 LTS focal |
Fixed 2:4.15.13+dfsg-0ubuntu0.20.04.8+esm2
|
|
| 18.04 LTS bionic | Ignored changes too intrusive | |
| 16.04 LTS xenial | Ignored end of ESM support, was needs-triage | |
| 14.04 LTS trusty | Ignored changes too intrusive |
Get expanded security coverage with Ubuntu Pro
Reduce your average CVE exposure time from 98 days to 1 day with expanded CVE patching, ten-years security maintenance and optional support for the full stack of open-source applications. Free for personal use.
Get Ubuntu Pro 30-day free trialNotes
mdeslaur
This is a non-default configuration where the "check password script" configuration item needs to be configured with the "%u" substitution character. This is not the case on Ubuntu. In addition, the samba-dcerpcd service would need to be configured in a non-default way.
Severity score breakdown
CVSS version: CVSS v3.0
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
References
Related Ubuntu Security Notices (USN)
- USN-8306-1
- Samba vulnerabilities
- 26 May 2026