CVE-2023-3255VulnerabilityPublished 13 Sep 2023Updated 8 Nov 2025

CVE-2023-3255: Red Hat Enterprise Linux 8 · Infinite Loop

Affects Red Hat Enterprise Linux 8Source CVE Database V5

Not known to be exploited · CVSS 6.5 Medium.

Data as of 26 Oct 2026, 06:26 UTC

CVSS 3.1 base score

6.5Medium

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

EPSS: 1.8% chance of exploitation in 30 days – higher than 79% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.

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

Attack Vector: Network
Attack Complexity: Low
Privileges Required: Low
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: 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: 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: 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 13 Sep 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-2023-3255, European organizations should take the following specific actions: 1) Apply the latest security patches and updates provided by Red Hat for Red Hat Enterprise Linux 8 and QEMU as soon as they become available to fix the infinite loop condition. 2) Restrict VNC server access to trusted and authenticated users only, enforcing strong authentication mechanisms such as multi-factor authentication to reduce the attack surface. 3) Disable clipboard sharing over VNC if it is not required, as this feature is the attack vector for the vulnerability. 4) Monitor VNC server logs and network traffic for unusual clipboard activity or repeated connection attempts that could indicate exploitation attempts. 5) Implement network segmentation and firewall rules to limit VNC access to only necessary systems and users. 6) Consider alternative remote management tools or VNC implementations that do not exhibit this vulnerability if patching is delayed. 7) Conduct regular vulnerability assessments and penetration tests focusing on virtualization infrastructure to identify and remediate similar issues proactively.

Description

A flaw was found in the QEMU built-in VNC server while processing ClientCutText messages. A wrong exit condition may lead to an infinite loop when inflating an attacker controlled zlib buffer in the `inflate_buffer` function. This could allow a remote authenticated client who is able to send a clipboard to the VNC server to trigger a denial of service.

Impact

The primary impact of CVE-2023-3255 is a denial of service condition that can disrupt the availability of virtual machines running on Red Hat Enterprise Linux 8 hosts using QEMU with the built-in VNC server. For European organizations, this could lead to temporary outages of critical virtualized infrastructure, affecting business continuity, especially in sectors relying heavily on virtualization such as finance, telecommunications, government, and cloud service providers. Since the attack requires authenticated access to the VNC server clipboard feature, the risk is higher in environments where VNC access is granted to multiple users or where authentication controls are weak. The lack of confidentiality or integrity impact reduces the risk of data breaches or system compromise, but the availability disruption could still cause operational and reputational damage. Organizations with high availability requirements or those operating critical infrastructure should consider this vulnerability significant enough to warrant prompt remediation. The absence of known exploits in the wild reduces immediate risk but does not eliminate the potential for future exploitation.

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Exploitation evidence

What to do

Description

AI analysisMachine-generated, updated 8 Nov 2025, 07:48 UTC

Technical details

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