VulnerabilityPublished 29 Jan 2024Updated 20 Nov 2025

CVE-2023-40550: Red Hat Enterprise Linux 7 · Out-of-bounds Read

Affects Red Hat Enterprise Linux 7Source CVE Database V5

Not known to be exploited · CVSS 5.5 Medium.

Data as of 26 Oct 2026, 14:05 UTC

CVSS 3.1 base score

5.5Medium

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:L/UI:N/S:U/C:H/I:N/A:N

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

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: 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: High: There is total loss of confidentiality, resulting in all resources within the impacted component being divulged to the attacker. Alternatively, access to only some restricted information is obtained, but the disclosed information presents a direct, serious impact.
Integrity: None: There is no loss of integrity within 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 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 correct the out-of-bounds read in Shim's SBAT validation logic.
Restrict local access to Red Hat Enterprise Linux 7 systems to trusted and authorized personnel only, minimizing the risk of exploitation by low-privilege users.
Implement strict access controls and monitoring on systems that use Shim for secure boot, including auditing boot logs and access attempts.
Consider upgrading to newer supported versions of Red Hat Enterprise Linux where possible, as they may include improved secure boot components and security fixes.
Use hardware-based security features such as TPM (Trusted Platform Module) and secure boot policies to strengthen boot integrity and reduce attack vectors.
Educate system administrators about the vulnerability and the importance of securing the boot process and local access.
Employ endpoint detection and response (EDR) solutions to detect anomalous behavior that could indicate attempts to exploit boot-level vulnerabilities.
Review and limit the use of shared or multi-user systems running RHEL 7 to reduce exposure to local privilege exploitation.

Description

An out-of-bounds read flaw was found in Shim when it tried to validate the SBAT information. This issue may expose sensitive data during the system's boot phase.

Impact

The primary impact of CVE-2023-40550 is the potential exposure of sensitive data during the system boot process on affected Red Hat Enterprise Linux 7 systems. For European organizations, this could lead to leakage of confidential information such as cryptographic keys, secure boot parameters, or other protected memory contents, undermining the confidentiality of critical systems. Although the vulnerability does not affect system integrity or availability, the exposure of sensitive data could facilitate further attacks or unauthorized access if leveraged by malicious insiders or attackers with local access. Sectors with high security requirements, including government, finance, telecommunications, and critical infrastructure operators in Europe, may face increased risks if their RHEL 7 systems are unpatched. The requirement for local access and low privileges limits the attack surface but does not eliminate risk in environments where multiple users have access or where attackers have already gained limited footholds. The lack of known exploits reduces immediate threat levels but does not preclude future exploitation attempts. Overall, the vulnerability could weaken trust in secure boot mechanisms and complicate compliance with data protection regulations such as GDPR if sensitive data is exposed.

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Exploitation evidence

What to do

Description

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

Technical details

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