What is the CVSS score of CVE-2023-6816?

CVE-2023-6816 has a CVSS 3.1 base score of 9.8 (Critical). CVSS vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H. EPSS exploitation probability: 3.3%.

How to fix or mitigate CVE-2023-6816?

Within 24 hours: Identify all affected systems running X.Org server. Both DeviceFocusEvent and the XIQueryPointer r and apply vendor patches immediately. If patching is delayed, consider network segmentation to limit exposure.

Debian Linux CVE-2023-6816

CRITICAL

Out-of-bounds Write (CWE-787)

2024-01-18 secalert@redhat.com

Buffer Overflow Debian Red Hat Debian Linux Enterprise Linux Desktop Enterprise Linux Server Enterprise Linux Workstation Fedora X Server Xwayland X Org Fedoraproject

9.8

CVSS 3.1 · NVD

View

Vulnerability Assessment

Weakness	CWE CWE-787 OWASP Top 10:2025 A06:2021 - Vulnerable and Outdated Components ASVS 5.0 V15 - Secure Coding and Architecture Bounds checking, write limits MITRE ATT&CK 2 techniques across 2 tactics: Execution, Privilege Escalation The technique list with ATT&CK links and the kill-chain view is part of the Basic plan and up. Sign in to read
Impact	Despite the critical CVSS 9.8 score indicating network-exploitable, no-authentication-required remote code execution, the real-world risk appears moderate based on multiple signals. The EPSS score of 3.26% (87th percentile) suggests above-average but not extreme exploitation likelihood. The vulnerability is not listed in CISA KEV, indicating no known active exploitation. The network attack vector (AV:N) with low complexity (AC:L) and no required privileges (PR:N) or user interaction (UI:N) makes it theoretically dangerous, but the specific conditions required (malicious button mappings in X11 protocol) and the availability of patches since early 2024 reduce practical risk for patched systems.
Exploit ScenarioDerived	An attacker could craft malicious X11 protocol messages that map logical buttons to values exceeding the allocated buffer size, triggering a heap overflow when DeviceFocusEvent or XIQueryPointer processes these mappings. This could allow remote code execution on the X.Org Server with the privileges of the X server process, typically root or a dedicated system user. No public proof-of-concept exists, but the network-accessible nature and low attack complexity make exploitation feasible for skilled attackers with X11 protocol knowledge.

Act Now Prioritize within 24-48h. Why: CRITICAL severity.

No patch listed yet 3.3% exploitation probability (EPSS)

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AnalysisAIv1 – Mar 19, 2026

A heap overflow vulnerability exists in X.Org Server and Xwayland where improper memory allocation for logical button mappings allows remote attackers to execute arbitrary code with high privileges. The flaw affects multiple Linux distributions including RHEL 7, Fedora 39, and Debian 10, with a critical CVSS score of 9.8 and an EPSS score of 3.26% (87th percentile), indicating moderate real-world exploitation likelihood. Multiple security advisories have been issued by Red Hat with patches available, though no evidence of active exploitation (not in KEV) or public proof-of-concept exists.

RemediationAI

Apply the vendor-provided security updates immediately, with Red Hat patches available via advisories RHSA-2024:0320, RHSA-2024:0557, RHSA-2024:0558, RHSA-2024:0597, RHSA-2024:0607, RHSA-2024:0614, RHSA-2024:0617, RHSA-2024:0621, RHSA-2024:0626, RHSA-2024:0629, RHSA-2024:2169, RHSA-2024:2170, RHSA-2024:2995, RHSA-2024:2996, and RHSA-2025:12751 (see https://access.redhat.com/errata/ for details). For systems that cannot be immediately patched, consider restricting network access to X11 services (typically port 6000) at the firewall level and disabling remote X11 connections where not required, though these are only partial mitigations for a memory corruption vulnerability.

Affects your stack

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Technical ContextAI · show details

The vulnerability affects X.Org X Server (all versions) and Xwayland (all versions) as identified by CPE entries cpe:2.3:a:x.org:x_server and cpe:2.3:a:x.org:xwayland. The flaw is classified as CWE-787 (Out-of-bounds Write), occurring in the DeviceFocusEvent and XIQueryPointer reply mechanisms which contain bit representations for each logical button currently pressed. While the X11 protocol allows buttons to be mapped to values up to 255, the X.Org Server only allocates memory based on the actual number of buttons on the device, creating a heap buffer overflow condition when higher button values are used.

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Exploit and PoC references, threat intelligence from 22 sources

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Severity by source

NVD PRIMARY 9.8 CRITICAL

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

Primary rating from NVD · only source for this CVE.

CVSS VectorNVD

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

None

Scope

Unchanged

Confidentiality

High

Integrity

High

Availability

High

DescriptionCVE.org

A flaw was found in X.Org server. Both DeviceFocusEvent and the XIQueryPointer reply contain a bit for each logical button currently down. Buttons can be arbitrarily mapped to any value up to 255, but the X.Org Server was only allocating space for the device's particular number of buttons, leading to a heap overflow if a bigger value was used.

Executive ViewAI

Why It Matters

Organizations using A flaw face critical risk from CVE-2023-6816, a out-of-bounds write vulnerability rated CVSS 9.8. Exploitation could allow attackers to corrupt memory, crash the application, or potentially execute arbitrary code. Organizations should apply vendor updates immediately when available and implement compensating controls in the interim.

Business Impact: Severe

Compensating Controls

Apply vendor patch. If immediate patching is not feasible: (1) Enable ASLR and DEP where available; (2) Implement network segmentation; (3) Monitor for exploitation indicators.

Threat Intelligence Overview

EPSS Score

3.3%

Top 13% exploitable

Data Quality

3 sources

Confidence: Low

NVD

CVE.org

EPSS

How this decision was reached

The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.

SignalValue

Severity CRITICAL

CISA KEV No

Public POC No

EPSS 3.3%

Patch available No

Active threat No

Deciding rule

CRITICAL severity

What every action level means

Emergency Immediate action required. Criteria: CRITICAL + in CISA KEV (actively exploited) without patch, OR CRITICAL + EPSS > 30% without patch, OR CRITICAL + active threat signals without patch.

Act Now Prioritize within 24-48h. Criteria: in KEV with patch available, OR CRITICAL + public POC, OR HIGH + EPSS > 10%, OR CRITICAL + active threat, OR any CRITICAL severity.

This Week Schedule remediation this week. Criteria: HIGH severity (CVSS 7.0-8.9). Patch within normal change window.

This Month Plan within 30 days. Criteria: MEDIUM severity (CVSS 4.0-6.9), lower exploitation probability. Include in regular patch cycle.

Monitor Track and reassess. Criteria: LOW severity (CVSS 0.1-3.9), minimal exploitation risk. No immediate action needed.

SSVC AssessmentENISA

SSVC Decision· derived

Out-of-Cycle

Exploitation· derived

None

System Exposure· derived

Open

Automatable· derived

Yes

Human Impact

Very High

Priority Score

Low Medium High Critical

KEV: 0

EPSS: +3

CVSS: +49

PoC: 0

Weaponized: 0

Threat intel: 0

Gov advisory: 0

Attack Technique

Buffer Overflow HIGH

A buffer overflow occurs when a program writes more data to a memory buffer than it was allocated to hold, causing the excess data to spill into adjacent memory regions.