Red Hat Enterprise Linux 10: Improper Neutralization of Special Elements used in an OS Command
CVE-2026-4408 is a critical-severity improper neutralization of special elements used in an OS command vulnerability in Red Hat Enterprise Linux 10 from Red Hat, with a CVSS 3.1 base score of 9.8 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. There is no confirmed exploitation so far. EPSS estimates a 46.9% chance of exploitation within 30 days, which is in the top 1.15% of all scored CVEs.
Critical severity: a successful attack would have severe impact.
What to do
- Update Samba to 4.21.0 or a later version.
- Read the advisory on bugzilla.samba.org for workarounds and exact fixed builds.
- Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.
Affected products and versions
Version data comes from the organisation that assigned the CVE; 4 further products are omitted here. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- NetworkCan be exploited remotely over a network, including the internet.
- Attack complexity
- LowNo special conditions are needed; the attack works reliably.
- Privileges required
- NoneNo account or login is needed.
- User interaction
- NoneNo action by a victim is required.
- Scope
- UnchangedImpact stays within the vulnerable component.
- Confidentiality
- HighAll data handled by the component can be read.
- Integrity
- HighData or code can be modified at will.
- Availability
- HighThe component can be taken down completely.
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H. Scored by NVD.
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 3.1 | 9.0 | Critical | CNA (redhat.com) |
| CVSS 3.1 | 9.8 | Critical | NVD |
| CVSS 3.1 | 9.0 | Critical | CNA |
Official 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.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Improper Neutralization of Special Elements used in an OS Command
The product constructs all or part of an OS command using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify the intended OS command before it is sent to a downstream component.
How developers prevent this class of flaw
- If at all possible, use library calls rather than external processes to recreate the desired functionality.
- For any data that will be used to generate a command to be executed, keep as much of that data out of external control as possible. For example, in web applications, this may require storing the data locally in the session's state instead of sending it out to the client in a hidden form field.
- For any security checks that are performed on the client side, ensure that these checks are duplicated on the server side, in order to avoid CWE-602. Attackers can bypass the client-side checks by modifying values after the checks have been performed, or by changing the client to remove the client-side checks entirely. Then, these modified values would be submitted to the server.
More Improper Neutralization of Special Elements used in an OS Command vulnerabilities (CWE-78)
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: none, automatable: no, technical impact: total).
- Record last changed materially (score, affected products, status or references).
References
Advisories
- bugzilla.samba.org/show_bug.cgi?id=16034Issue Tracking
Third-party and government advisories
- access.redhat.com/security/cve/CVE-2026-4408Third Party Advisory
- bugzilla.redhat.com/show_bug.cgi?id=2479762Issue Tracking, Third Party Advisory
Other references
- access.redhat.com/errata/RHSA-2026:22644Issue Tracking
- access.redhat.com/errata/RHSA-2026:22963Issue Tracking
- access.redhat.com/errata/RHSA-2026:25049
- access.redhat.com/errata/RHSA-2026:25979
- access.redhat.com/errata/RHSA-2026:28053
- access.redhat.com/errata/RHSA-2026:28054
- access.redhat.com/errata/RHSA-2026:28055
- access.redhat.com/errata/RHSA-2026:28056
- access.redhat.com/errata/RHSA-2026:28057
- access.redhat.com/errata/RHSA-2026:28058
- access.redhat.com/errata/RHSA-2026:28132
- access.redhat.com/errata/RHSA-2026:29799
- access.redhat.com/errata/RHSA-2026:29833
- access.redhat.com/errata/RHSA-2026:29863
- access.redhat.com/errata/RHSA-2026:56786
Other vulnerabilities in Red Hat Enterprise Linux 10
- 8.8 High severity
- 7.5 High severity
- 7.5 High severity
- 7.9 High severity
- 7.3 High severity
- 7.5 High severity
Recent Improper Neutralization of Special Elements used in an OS Command vulnerabilities
- 9.9 Critical severity
- 8.6 High severity
- 8.6 High severity
- 7.8 High severity
- 8.6 High severity
- 7.0 High severity
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