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

Severity: medium (CVSS 6.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 1.3% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2023-11-03 · updated 2026-06-17
Weakness: CWE-276

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.

Affected products

Fedoraproject Fedora: 39
Red Hat Enterprise Linux: 8.0
RedHat Enterprise Linux Eus: 9.0
RedHat Storage: 3.0
Samba: before 4.17.12; from 4.18.0 before 4.18.8; from 4.19.0 before 4.19.1 — fixed in 4.17.12, 4.18.8, 4.19.1

How to fix

Upgrade to a fixed version: Samba 4.17.12, 4.18.8, 4.19.1. Check the vendor advisory for mitigations.

References

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