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

2026-10-01T02:16:17.947601+00:00

Affected: Red Hat Enterprise Linux 8, Red Hat Enterprise Linux 8.6 Extended Update Support, Red Hat Enterprise Linux 8.8 Extended Update Support, Red Hat Enterprise Linux 9, Red Hat Enterprise Linux 9.0 Extended Update Support, Red Hat Enterprise Linux 9.2 Extended Update Support, Red Hat Virtualization 4 for Red Hat Enterprise Linux 8, Red Hat Enterprise Linux 6, Red Hat Enterprise Linux 7, Red Hat Storage 3

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.

USN-6425-1 — samba vulnerabilities

2026-10-01T02:16:17.947822+00:00

Affected: Ubuntu:20.04:LTS: samba, Ubuntu:22.04:LTS: samba

Sri Nagasubramanian discovered that the Samba acl_xattr VFS module incorrectly handled read-only files. When Samba is configured to ignore system ACLs, a remote attacker could possibly use this issue to truncate read-only files. (CVE-2023-4091)

Andrew Bartlett discovered that Samba incorrectly handled the DirSync control. A remote attacker with an RODC DC account could possibly use this issue to obtain all domain secrets. (CVE-2023-4154)

Andrew Bartlett discovered that Samba incorrectly handled the rpcecho development server. A remote attacker could possibly use this issue to cause Samba to stop responding, resulting in a denial of service. (CVE-2023-42669)

Kirin van der Veer discovered that Samba incorrectly handled certain RPC service listeners. A remote attacker could possibly use this issue to cause Samba to start multiple incompatible RPC listeners, resulting in a denial of service. This issue only affected Ubuntu 22.04 LTS, and Ubuntu 23.04. (CVE-2023-42670)