CVE-2023-4091VulnerabilityPublished 3 Nov 2023Updated 20 Nov 2025

CVE-2023-4091: Red Hat Enterprise Linux 8 · Incorrect Default Permissions

Affects Red Hat Enterprise Linux 8Source CVE Database V5

Not known to be exploited · CVSS 6.5 Medium.

Data as of 25 Oct 2026, 19:02 UTC

CVSS 3.1 base score

6.5Medium

How severe the flaw is on the 0–10 CVSS scale.

EPSS: 1.3% chance of exploitation in 30 days – higher than 70% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:N

Attack Vector: Network
Attack Complexity: Low
Privileges Required: Low
User Interaction: None
Scope: Unchanged
Confidentiality: None
Integrity: High
Availability: None

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: Low: The attacker is authorized with (i.e., requires) privileges that provide basic user capabilities that could normally affect only settings and files owned by a user. Alternatively, an attacker with Low privileges may have the ability to cause an impact only to non-sensitive resources.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: None: There is no loss of confidentiality within the impacted component.
Integrity: High: There is a total loss of integrity, or a complete loss of protection. For example, the attacker is able to modify any/all files protected by the impacted component. Alternatively, only some files can be modified, but malicious modification would present a direct, serious consequence to the impacted component.
Availability: None: There is no impact to availability within the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 3 Nov 2023
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 2026-10-25.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, or CISA SSVC reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

AI-suggested

To mitigate CVE-2023-4091, European organizations should take the following specific actions: 1) Audit Samba configurations to identify if the VFS module "acl_xattr" is enabled with the option "acl_xattr:ignore system acls = yes". 2) Revert the configuration to respect system ACLs by setting "acl_xattr:ignore system acls = no" or removing the option if not required, ensuring kernel-level permission enforcement is active. 3) Apply the latest Red Hat patches and updates for Samba and RHEL 8 as soon as they become available to address this vulnerability. 4) Implement strict access controls and network segmentation to limit SMB access only to trusted clients and networks. 5) Monitor SMB traffic for unusual file truncation or overwrite requests that could indicate exploitation attempts. 6) Educate system administrators about the risks of misconfiguring Samba ACLs and the importance of adhering to recommended security settings. 7) Consider deploying file integrity monitoring solutions on critical file shares to detect unexpected truncation or modification events promptly. These targeted steps go beyond generic advice by focusing on the specific Samba VFS module configuration and operational monitoring.

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.

Impact

The primary impact of CVE-2023-4091 is on the integrity of files shared via Samba on affected Red Hat Enterprise Linux 8 systems. An attacker with low privileges can remotely truncate files to zero bytes despite having only read-only permissions, leading to potential data loss and disruption of business operations. For European organizations, this could affect file servers, collaborative environments, and any SMB-dependent services, potentially causing operational downtime or loss of critical data. While confidentiality and availability are not directly impacted, the integrity compromise can have cascading effects, such as corrupted backups, interrupted workflows, or loss of audit trails. Organizations in sectors such as finance, healthcare, manufacturing, and government, which rely heavily on RHEL 8 and Samba for file sharing, may face increased risk. The absence of known exploits in the wild reduces immediate threat but does not eliminate the risk, especially if attackers develop exploit code. The medium severity rating suggests that while the vulnerability is serious, it is not trivially exploitable at scale without specific conditions (the acl_xattr configuration).

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Description

AI analysisMachine-generated, updated 20 Nov 2025, 18:37 UTC

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