VulnerabilityPublished 29 Jan 2024Updated 20 Nov 2025

CVE-2023-40551: Red Hat Enterprise Linux 7 · Out-of-bounds Read

Affects Red Hat Enterprise Linux 7Source CVE Database V5

Not known to be exploited · CVSS 5.1 Medium.

Data as of 26 Oct 2026, 12:29 UTC

CVSS 3.1 base score

5.1Medium

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

EPSS: 0.3% chance of exploitation in 30 days – higher than 33% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.

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

Attack Vector: Local
Attack Complexity: Low
Privileges Required: High
User Interaction: None
Scope: Unchanged
Confidentiality: Low
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: High: The attacker is authorized with (i.e., requires) privileges that provide significant (e.g., administrative) control over the vulnerable component that could affect component-wide settings and files.
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: Low: There is some loss of confidentiality. Access to some restricted information is obtained, but the attacker does not have control over what information is obtained, or the amount or kind of loss is limited. The information disclosure does not cause a direct, serious loss to 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 26 Oct 2026.

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 or the CVSS exploit maturity 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

Apply official patches from Red Hat as soon as they become available to address the out-of-bounds read in Shim.
Restrict and monitor high-privilege local access to systems running RHEL 7 to reduce the risk of exploitation by insiders or attackers with elevated rights.
Implement strict boot process monitoring and logging to detect abnormal crashes or boot failures that could indicate exploitation attempts.
Use secure boot configurations and ensure the integrity of bootloader components to minimize the risk of tampering.
Employ host-based intrusion detection systems (HIDS) to alert on suspicious activities related to Shim or boot processes.
Regularly audit system access and privilege assignments to limit exposure to high-privilege local users.
Consider upgrading to newer supported versions of Red Hat Enterprise Linux where possible, as RHEL 7 is approaching end-of-life and may receive limited support.
Develop and test incident response plans that include recovery from boot-time failures to minimize downtime in case of exploitation.

Description

A flaw was found in the MZ binary format in Shim. An out-of-bounds read may occur, leading to a crash or possible exposure of sensitive data during the system's boot phase.

Impact

For European organizations, especially those running Red Hat Enterprise Linux 7 in production environments, this vulnerability poses a risk primarily to system availability and confidentiality during the boot process. A successful exploit could cause system crashes, leading to downtime and potential disruption of critical services. Exposure of sensitive data during boot could include bootloader or kernel-related information, which might be leveraged for privilege escalation or further attacks. Organizations in sectors such as finance, healthcare, energy, and government, which rely heavily on secure and stable Linux systems, could face operational risks and compliance challenges. The requirement for local high-privilege access limits the threat to insiders or attackers who have already compromised systems, but the potential impact on critical infrastructure makes it significant. Additionally, the vulnerability could affect automated or remote reboot processes, complicating recovery efforts. The medium severity rating suggests that while urgent exploitation is less likely, the vulnerability should not be ignored, especially in environments with stringent security requirements.

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Exploitation evidence

What to do

Description

AI analysisMachine-generated, updated 20 Nov 2025, 20:45 UTC

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