CVE-2023-40549VulnerabilityPublished 29 Jan 2024Updated 20 Nov 2025

CVE-2023-40549: Red Hat Enterprise Linux 7 · Out-of-bounds Read

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 35% 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

1. Monitor Red Hat advisories closely and apply official patches or updates for Shim as soon as they are released to remediate the vulnerability. 2. Restrict local system access to trusted and authenticated users only, using strong access controls and physical security measures to prevent unauthorized local access. 3. Implement strict user account management and privilege separation to minimize the risk of unprivileged users exploiting the flaw. 4. Employ system integrity monitoring and logging to detect abnormal Shim crashes or boot failures that could indicate exploitation attempts. 5. Consider upgrading to a newer Red Hat Enterprise Linux version where this vulnerability is not present or has been fixed, reducing exposure to legacy vulnerabilities. 6. In environments where secure boot is critical, validate the integrity of PE binaries before loading them, if feasible, to prevent crafted binaries from triggering the flaw. 7. Conduct regular security audits and penetration testing focusing on local privilege escalation and denial of service vectors to identify and mitigate related risks.

Description

An out-of-bounds read flaw was found in Shim due to the lack of proper boundary verification during the load of a PE binary. This flaw allows an attacker to load a crafted PE binary, triggering the issue and crashing Shim, resulting in a denial of service.

Impact

The primary impact of CVE-2023-40549 is a denial of service condition caused by Shim crashing when processing a crafted PE binary. For European organizations, this could lead to system unavailability, particularly in environments where Red Hat Enterprise Linux 7 is used in critical infrastructure, servers, or embedded systems relying on secure boot. The inability to boot or maintain system uptime could disrupt business operations, especially in sectors such as finance, healthcare, telecommunications, and government services. Since the vulnerability requires local access, the risk is higher in environments with multiple users or where attackers can gain physical or remote local access. Although confidentiality and integrity are not directly affected, the availability impact can have cascading effects on service delivery and operational continuity. Organizations using legacy systems or those slow to upgrade from RHEL 7 may face prolonged exposure. The lack of known exploits reduces immediate risk, but the medium severity score indicates that exploitation could be impactful if attackers gain local access.

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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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