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

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.

Published: 2023-11-03 Last update: 2024-11-21 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2023-4091 is rated Moderate Risk (48.9/100): CVSS Medium severity, with medium exploitation likelihood (EPSS 1.17%). Review affected assets and schedule remediation.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2023-4091

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-06-15 0.44% 1.17% +0.74%
2 2026-04-19 0.48% 0.44% -0.04%
3 2025-11-28 — 0.48% —

Full EPSS history (19 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2023-4091

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
6.5 3.1 MEDIUM
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:N Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:L)
A normal user session is enough; they don’t have to be admin.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:H)
They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:N)
Service keeps running; no real outage angle.
 2.8 3.6 [email protected]
6.5 3.1 MEDIUM
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:N Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:L)
A normal user session is enough; they don’t have to be admin.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:H)
They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:N)
Service keeps running; no real outage angle.
 2.8 3.6 [email protected]

Weakness enumeration for CVE-2023-4091

OS Trackers for CVE-2023-4091

vendor priority summary link
alpine — CVE-2023-4091: 1 source package rows (samba); 7 state rows across 7 repos (3.17-main, 3.18-main, 3.19-main, 3.20-main, 3.21-main, 3.22-main, edge-main); fixed 6, open 1. https://security.alpinelinux.org/vuln/CVE-2023-4091
debian not yet assigned CVE-2023-4091 not yet assigned priority: Debian including 1 source packages (samba), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 5. https://security-tracker.debian.org/tracker/CVE-2023-4091
gentoo high CVE-2023-4091: 1 GLSA(s) (202402-28), 1 atom(s) (net-fs/samba); latest impact high. https://bugs.gentoo.org/buglist.cgi?quicksearch=CVE-2023-4091
redhat medium — https://access.redhat.com/security/cve/CVE-2023-4091
suse medium — https://www.suse.com/security/cve/CVE-2023-4091/
ubuntu medium CVE-2023-4091 medium priority: Ubuntu including 1 source packages (samba), 12 status rows across 12 suites (bionic, focal, jammy, lunar, mantic, noble, oracular, plucky, questing, trusty, upstream, xenial): released 8, needs-triage 4. https://ubuntu.com/security/CVE-2023-4091

Affected software / configurations for CVE-2023-4091

Vendor Product Version Raw CPE
samba samba < 4.17.12 cpe:2.3:a:samba:samba:*:*:*:*:*:*:*:*
samba samba >= 4.18.0, < 4.18.8 cpe:2.3:a:samba:samba:*:*:*:*:*:*:*:*
samba samba >= 4.19.0, < 4.19.1 cpe:2.3:a:samba:samba:*:*:*:*:*:*:*:*
fedoraproject fedora 39 cpe:2.3:o:fedoraproject:fedora:39:*:*:*:*:*:*:*
redhat storage 3.0 cpe:2.3:a:redhat:storage:3.0:*:*:*:*:*:*:*
redhat enterprise_linux 8.0 cpe:2.3:o:redhat:enterprise_linux:8.0:*:*:*:*:*:*:*
redhat enterprise_linux_eus 9.0 cpe:2.3:o:redhat:enterprise_linux_eus:9.0:*:*:*:*:*:*:*

References for CVE-2023-4091

URL Tags
https://access.redhat.com/errata/RHSA-2023:6209 Third Party Advisory
https://access.redhat.com/errata/RHSA-2023:6744 Third Party Advisory
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 Third Party Advisory
https://bugzilla.redhat.com/show_bug.cgi?id=2241882 Issue Tracking
https://bugzilla.samba.org/show_bug.cgi?id=15439 Issue Tracking
https://www.samba.org/samba/security/CVE-2023-4091.html Vendor Advisory
https://lists.debian.org/debian-lts-announce/2024/04/msg00015.html
https://lists.fedoraproject.org/archives/list/[email protected]/message/ZUMVALLFFDFC53JZMUWA6HPD7HUGAP5I/
https://security.netapp.com/advisory/ntap-20231124-0002/
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