CVE-2023-6918VulnerabilityPublished 18 Dec 2023Updated 21 Nov 2025

CVE-2023-6918: Red Hat Enterprise Linux 8 · Unchecked Return Value

Affects Red Hat Enterprise Linux 8Source CVE Database V5

Not known to be exploited · CVSS 3.7 Low.

Data as of 26 Oct 2026, 06:26 UTC

CVSS 3.1 base score

3.7Low

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

EPSS: 1.4% chance of exploitation in 30 days – higher than 72% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.

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

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

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: High: A successful attack depends on conditions beyond the attacker's control. That is, a successful attack cannot be accomplished at will, but requires the attacker to invest in some measurable amount of effort in preparation or execution against the vulnerable component before a successful attack can be expected. For example, a successful attack may require an attacker to: gather knowledge about the environment in which the vulnerable target/component exists; prepare the target environment to improve exploit reliability; or inject themselves into the logical network path between the target and the resource requested by the victim in order to read and/or modify network communications (e.g., a man in the middle attack).
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: Low: Performance is reduced or there are interruptions in resource availability. Even if repeated exploitation of the vulnerability is possible, the attacker does not have the ability to completely deny service to legitimate users. The resources in the impacted component are either partially available all of the time, or fully available only some of the time, but overall there is no direct, serious consequence to the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 18 Dec 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 2026-10-26.

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-2023-6918, European organizations should: 1) Monitor Red Hat advisories and promptly apply patches or updates to libssh and Red Hat Enterprise Linux 8 as they become available. 2) Implement robust error handling and validation in cryptographic operations within custom or third-party software that interfaces with libssh to prevent unchecked return values. 3) Employ network segmentation and access controls to limit exposure of SSH services to trusted networks and users, reducing the attack surface. 4) Use SSH connection monitoring and alerting tools to detect abnormal connection terminations that may indicate exploitation attempts. 5) Consider deploying redundancy and failover mechanisms for critical SSH-dependent services to maintain availability during potential disruptions. 6) Conduct regular vulnerability assessments and penetration testing focusing on SSH services to identify and remediate related weaknesses proactively.

Description

A flaw was found in the libssh implements abstract layer for message digest (MD) operations implemented by different supported crypto backends. The return values from these were not properly checked, which could cause low-memory situations failures, NULL dereferences, crashes, or usage of the uninitialized memory as an input for the KDF. In this case, non-matching keys will result in decryption/integrity failures, terminating the connection.

Impact

For European organizations, the primary impact of CVE-2023-6918 is on the availability of SSH connections, which are critical for remote management and secure communications in enterprise and infrastructure environments. Organizations relying heavily on Red Hat Enterprise Linux 8 for servers, especially those managing critical infrastructure, cloud services, or enterprise applications, may experience service disruptions due to unexpected SSH connection terminations. While the vulnerability does not directly compromise data confidentiality or integrity, the denial-of-service aspect could hinder operational continuity, particularly in automated environments where SSH is used for orchestration or remote execution. The low severity and absence of known exploits reduce immediate risk, but unpatched systems remain vulnerable to potential future exploitation attempts. European entities with stringent uptime requirements or those in sectors such as finance, healthcare, and government should prioritize remediation to avoid operational impacts.

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Exploitation evidence

What to do

Description

AI analysisMachine-generated, updated 21 Nov 2025, 07:01 UTC

Technical details

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