# CVE-2026-109411: Samba: access control bypass via vfs_ceph_rgw case-insensitive open

Status: published. Published: 2026-10-28. Updated: 2026-11-04.

An access control bypass flaw was identified in Samba's vfs_ceph_rgw module in it's openat() function. An authenticated user can bypass access controls to read or overwrite restricted files on shares configured with the experimental vfs_ceph_rgw module. When a client requests an existing file using mismatched character casing, the module fails to perform a case-insensitive lookup correctly, causing the server to treat the operation as creating a new file. As a result, the server skips standard permission checks on the existing file, allowing the attacker to access or overwrite sensitive data owned by other users.

## Remediation

- workaround: Only shares configured with the vfs_ceph_rgw module are affected.

To mitigate this vulnerability, disable the experimental `vfs_ceph_rgw` module on any configured Samba shares. Edit `/etc/samba/smb.conf` to remove `ceph_rgw` from the `vfs objects` setting under the relevant share sections, then reload the Samba service:

```
systemctl reload smb
```

Warning: Reloading or restarting the `smb` service may briefly interrupt active client sessions. Additionally, removing this module disables Ceph RGW integration for the affected shares.

Setting ```case sensitive = yes``` on affected shares avoids the vulnerability, because the differently-cased name is then treated as a distinct object rather than resolving to the existing file. 

Note: This changes share behavior for clients that rely on case-insensitive name handling. (source: CNA: redhat)

## Affected products and versions

- Samba / Samba (samba): ≥ 4.25.0; < 4.25.1 (affected, semver). Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux 10 (samba): Version range not reported. 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 Enterprise Linux 8 (samba): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux 9 (samba): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat OpenShift Container Platform 4 (openshift/ose-rhel-coreos-8): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat OpenShift Container Platform 4 (openshift/ose-rhel-coreos-9): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat OpenShift Container Platform 5 (openshift/ose-rhel-coreos-9): Version range not reported. Source: CNA: redhat

## Severity and prioritization

- CVSS 3.1: 8.1 (high); CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N; source: CNA: redhat

- CVSS 3.1: 8.1 (high); CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N; source: NVD: secalert@redhat.com

- CISA KEV: No listing in collected sources

- EPSS: 0.65% as of 2026-11-04; percentile 51.25%

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

- Weaknesses: CWE-178

## Exploit evidence

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

## References

- https://access.redhat.com/security/cve/CVE-2026-109411 (CNA: redhat; vdb-entry, x_refsource_REDHAT)

- https://attachments.samba.org/attachment.cgi?id=19294 (CNA: redhat)

- https://attachments.samba.org/attachment.cgi?id=19295 (CNA: redhat)

- https://bugzilla.redhat.com/show_bug.cgi?id=2552136 (CNA: redhat; issue-tracking, x_refsource_REDHAT)

- https://bugzilla.samba.org/show_bug.cgi?id=16276 (CNA: redhat)

- https://access.redhat.com/security/cve/CVE-2026-109411 (secalert@redhat.com)

- https://attachments.samba.org/attachment.cgi?id=19294 (secalert@redhat.com)

- https://attachments.samba.org/attachment.cgi?id=19295 (secalert@redhat.com)

- https://bugzilla.redhat.com/show_bug.cgi?id=2552136 (secalert@redhat.com)

- https://bugzilla.samba.org/show_bug.cgi?id=16276 (secalert@redhat.com)

## Provenance

- CNA: redhat: https://www.cve.org/CVERecord?id=CVE-2026-109411; retrieved 2026-11-04; source updated 2026-11-04

- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-109411; retrieved 2026-11-05; source updated 2026-11-04

- FIRST EPSS: https://api.first.org/data/v1/epss?cve=CVE-2026-109411; retrieved 2026-11-04; source updated Not reported

Revision: 9aea1cec9dc3c649d6537c6b4881cd27ec30d67629eadf39074b4b3849484f79

Canonical: https://y2.dev/cve/CVE-2026-109411

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