# CVE-2023-4091: Samba: smb clients can truncate files with read-only permissions

Status: published. Published: 2023-11-03. Updated: 2026-11-07.

A vulnerability was discovered in Samba, where the flaw allows SMB clients to truncate files, even with read-only permissions when the Samba VFS module "acl_xattr" is configured with "acl_xattr:ignore system acls = yes". The SMB protocol allows opening files when the client requests read-only access but then implicitly truncates the opened file to 0 bytes if the client specifies a separate OVERWRITE create disposition request. The issue arises in configurations that bypass kernel file system permissions checks, relying solely on Samba's permissions.

## Remediation

- workaround: The vulnerability is most commonly associated with the "acl_xattr" module and can be mitigated by setting:
~~~
"acl_xattr:ignore system acls = no"
~~~ (source: CNA: redhat)

## Affected products and versions

- Red Hat / Red Hat Enterprise Linux 8 (samba): ≥ 0:4.18.6-2.el8_9; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux 8.6 Extended Update Support (samba): ≥ 0:4.15.5-13.el8_6; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux 8.8 Extended Update Support (samba): ≥ 0:4.17.5-4.el8_8; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux 9 (samba): ≥ 0:4.18.6-101.el9_3; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux 9.0 Extended Update Support (samba): ≥ 0:4.15.5-111.el9_0; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux 9.2 Extended Update Support (samba): ≥ 0:4.17.5-104.el9_2; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat Virtualization 4 for Red Hat Enterprise Linux 8 (samba): ≥ 0:4.15.5-13.el8_6; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux 6 (samba): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux 6 (samba4): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux 7 (samba): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat Storage 3 (samba): Version range not reported. Source: CNA: redhat

## Severity and prioritization

- CVSS 3.1: 6.5 (medium); CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:N; source: CNA: redhat

- CISA KEV: No listing in collected sources

- EPSS: 1.33% as of 2026-11-07; percentile 71.32%

- SSVC: exploitation none; automatable no; technical impact total; source ADP: CISA-ADP

- Weaknesses: CWE-276

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://access.redhat.com/errata/RHSA-2023:6209 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/errata/RHSA-2023:6744 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/errata/RHSA-2023:7371 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/errata/RHSA-2023:7408 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/errata/RHSA-2023:7464 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/errata/RHSA-2023:7467 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/security/cve/CVE-2023-4091 (CNA: redhat; vdb-entry, x_refsource_REDHAT)

- https://bugzilla.redhat.com/show_bug.cgi?id=2241882 (CNA: redhat; issue-tracking, x_refsource_REDHAT)

- https://bugzilla.samba.org/show_bug.cgi?id=15439 (CNA: redhat)

- https://www.samba.org/samba/security/CVE-2023-4091.html (CNA: redhat)

- https://access.redhat.com/errata/RHSA-2023:6209 (ADP: CVE; vendor-advisory, x_refsource_REDHAT, x_transferred)

- https://access.redhat.com/errata/RHSA-2023:6744 (ADP: CVE; vendor-advisory, x_refsource_REDHAT, x_transferred)

- https://access.redhat.com/errata/RHSA-2023:7371 (ADP: CVE; vendor-advisory, x_refsource_REDHAT, x_transferred)

- https://access.redhat.com/errata/RHSA-2023:7408 (ADP: CVE; vendor-advisory, x_refsource_REDHAT, x_transferred)

- https://access.redhat.com/errata/RHSA-2023:7464 (ADP: CVE; vendor-advisory, x_refsource_REDHAT, x_transferred)

- https://access.redhat.com/errata/RHSA-2023:7467 (ADP: CVE; vendor-advisory, x_refsource_REDHAT, x_transferred)

- https://access.redhat.com/security/cve/CVE-2023-4091 (ADP: CVE; vdb-entry, x_refsource_REDHAT, x_transferred)

- https://bugzilla.redhat.com/show_bug.cgi?id=2241882 (ADP: CVE; issue-tracking, x_refsource_REDHAT, x_transferred)

- https://bugzilla.samba.org/show_bug.cgi?id=15439 (ADP: CVE; x_transferred)

- https://lists.debian.org/debian-lts-announce/2024/04/msg00015.html (ADP: CVE; x_transferred)

- https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/ZUMVALLFFDFC53JZMUWA6HPD7HUGAP5I/ (ADP: CVE; x_transferred)

- https://security.netapp.com/advisory/ntap-20231124-0002/ (ADP: CVE; x_transferred)

- https://www.samba.org/samba/security/CVE-2023-4091.html (ADP: CVE; x_transferred)

## Provenance

- CNA: redhat: https://www.cve.org/CVERecord?id=CVE-2023-4091; retrieved 2026-11-07; source updated 2026-11-07

- FIRST EPSS: https://api.first.org/data/v1/epss?cve=CVE-2023-4091; retrieved 2026-11-07; source updated Not reported

Revision: 6e8d7819ae6fb01e443a2cbe2e45108bce1bff7542704ee4a6b18274c133ce64

Canonical: https://y2.dev/cve/CVE-2023-4091

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