CVE-2023-40546VulnerabilityPublished 29 Jan 2024Updated 20 Nov 2025

CVE-2023-40546: Red Hat Enterprise Linux 7 · NULL Pointer Dereference

Affects Red Hat Enterprise Linux 7Source CVE Database V5

Not known to be exploited · CVSS 6.2 Medium.

Data as of 25 Oct 2026, 19:02 UTC

CVSS 3.1 base score

6.2Medium

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

EPSS: 0.4% chance of exploitation in 30 days – higher than 37% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.

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

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

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

Attack Vector: Local: The vulnerable component is not bound to the network stack and the attacker’s path is via read/write/execute capabilities. Either: the attacker exploits the vulnerability by accessing the target system locally (e.g., keyboard, console), or remotely (e.g., SSH); or the attacker relies on User Interaction by another person to perform actions required to exploit the vulnerability (e.g., tricking a legitimate user into opening a malicious document).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
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: None: There is no loss of integrity within the impacted component.
Availability: High: There is total loss of availability, resulting in the attacker being able to fully deny access to resources in the impacted component; this loss is either sustained (while the attacker continues to deliver the attack) or persistent (the condition persists even after the attack has completed). Alternatively, the attacker has the ability to deny some availability, but the loss of availability presents a direct, serious consequence to the impacted component (e.g., the attacker cannot disrupt existing connections, but can prevent new connections; the attacker can repeatedly exploit a vulnerability that, in each instance of a successful attack, leaks a only small amount of memory, but after repeated exploitation causes a service to become completely unavailable).

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 29 Jan 2024
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-2023-40546, organizations should: 1) Monitor Red Hat advisories closely and apply official patches or updates for Shim as soon as they become available. 2) Audit systems using Red Hat Enterprise Linux 7 to identify those relying on Shim for secure boot and prioritize patching on these critical systems. 3) Implement robust access controls to limit local access to trusted users only, reducing the risk of exploitation. 4) Enable detailed logging and monitoring for Shim-related errors and crashes to detect potential exploitation attempts early. 5) Test boot processes in controlled environments after patching to ensure stability and prevent unexpected downtime. 6) Consider upgrading to newer supported versions of Red Hat Enterprise Linux where possible, as they may not be affected by this vulnerability. 7) Develop incident response plans that include recovery procedures for boot failures related to Shim crashes. These steps go beyond generic advice by focusing on secure boot environments, local access restrictions, and proactive monitoring specific to the vulnerability's characteristics.

Description

A flaw was found in Shim when an error happened while creating a new ESL variable. If Shim fails to create the new variable, it tries to print an error message to the user; however, the number of parameters used by the logging function doesn't match the format string used by it, leading to a crash under certain circumstances.

Impact

The primary impact of CVE-2023-40546 is a denial of service caused by Shim crashing during secure boot operations. For European organizations, especially those running Red Hat Enterprise Linux 7 in production environments, this could lead to system unavailability or boot failures, affecting business continuity. Critical infrastructure sectors such as energy, finance, telecommunications, and government agencies that rely on secure boot for system integrity verification may experience operational disruptions. Although the vulnerability does not allow data compromise or privilege escalation, the inability to boot systems or repeated crashes could delay incident response and recovery efforts. The local access requirement limits remote exploitation, but insider threats or compromised local accounts could trigger the issue. The lack of user interaction needed means automated or scripted attacks by local adversaries are feasible. Overall, the impact is significant for availability and operational stability but does not extend to confidentiality or integrity breaches.

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Exploitation evidence

What to do

Description

AI analysisMachine-generated, updated 20 Nov 2025, 20:44 UTC

Technical details

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