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MEDIUM

Samba: vfs_worm does not block directory modification

Published May 27, 2026

Description

A flaw was found in Samba’s vfs_worm module. The module is intended to provide write-once, read-many (WORM) protections by preventing modification of files after a configurable grace period. Due to insufficient validation during rename operations, an authenticated user with write access to a share could overwrite a protected file by renaming a newly created file over the existing WORM-protected file.

Affected products

Remediation

Vendor solution

Administrators can mitigate this issue by:

Setting read-only permissions on protected files at the underlying filesystem level will prevent modifications.

Configuring ```worm:grace_period = 0``` (zero or less) in smb.conf will eliminate the writable grace period (will eliminate the window in which the rename can happen), understanding that this may impact workflows requiring multi-step file creation.

Red Hat statement

This vulnerability is rated Moderate severity because exploitation requires authenticated write access to a Samba share already configured to permit file creation and modification. The flaw affects the vfs_worm module, which provides additional immutability protections for files after a configurable grace period. Due to improper handling of rename operations, a user with existing write permissions could overwrite files that should have become immutable under the WORM policy. The vulnerability does not bypass underlying filesystem access controls or grant additional privileges beyond those already assigned to the authenticated user. However, because the primary purpose of the vfs_worm module is to protect file integrity, the ability to modify protected files results in a high integrity impact.

Red Hat mitigation

Administrators can mitigate this issue by: Setting read-only permissions on protected files at the underlying filesystem level will prevent modifications. Configuring ```worm:grace_period = 0``` (zero or less) in smb.conf will eliminate the writable grace period (will eliminate the window in which the rename can happen), understanding that this may impact workflows requiring multi-step file creation.

Metrics

Weaknesses (1)

CWE-280

References (28)

Change history (0)

No recorded changes yet.

Sources
CVE.org / MITRE
Status PUBLISHED
Assigner redhat
Published May 27, 2026
Updated Oct 1, 2026
Reserved Feb 11, 2026
Link CVE-2026-2340
CISA Vulnrichment
Updated May 29, 2026
NVD
Status Modified
Modified Sep 17, 2026
Link CVE-2026-2340
Red Hat
Severity Moderate
Public date May 27, 2026
Links CVE-2026-2340 - Bugzilla