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CVE Record

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

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.

CriticalCVSS 9.8Not KEV-listedUpdated
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Glexia's TakeAutomated analysiscritical

Security readout for executives and security teams

Plain-English summary

CVE-2023-6816 is a critical heap overflow in X.Org server-related components. A crafted button mapping condition can make the server write beyond allocated memory. For business leaders, the concern is high-impact compromise risk on affected Red Hat graphical, Xwayland, or TigerVNC systems, especially where remote graphical access is enabled.

Executive priority

Treat as urgent for affected Red Hat graphical or remote desktop environments. The issue carries critical impact scoring, and vendor advisories exist. Focus first on externally reachable or broadly accessible systems, then complete fleet-wide package validation and updates.

Technical view

DeviceFocusEvent and XIQueryPointer replies track logical buttons currently down. The server allowed button mappings up to 255 but allocated based on the device button count, creating a heap buffer overflow. The bundle maps this to CWE-787 and a CVSS 3.1 score of 9.8 with network, unauthenticated, no-user-interaction characteristics.

Likely exposure

Exposure is most likely on Red Hat Enterprise Linux 7, 8, 9, and listed EUS/AUS/TUS variants running xorg-x11-server, xorg-x11-server-Xwayland, or tigervnc. RHEL 6 ELS TigerVNC is listed affected; RHEL 6 xorg-x11-server status is unknown in the bundle.

Exploitation context

The bundle does not show CISA KEV listing or cited evidence of active exploitation. The CVSS vector indicates low-complexity network exploitation without authentication or user interaction, but the provided sources do not confirm public exploitation, weaponization, or exploit maturity.

Researcher notes

The key bug is allocation mismatch: logical button values may reach 255 while storage was sized for the physical device button count. Avoid assuming non-Red Hat products, exploit availability, or specific fixed builds beyond the supplied Red Hat advisories and affected package records.

Mitigation direction

  • Apply the relevant Red Hat RHSA updates for affected xorg-x11-server, Xwayland, and tigervnc packages.
  • Prioritize systems exposing X, Xwayland, or VNC-style graphical access across network boundaries.
  • Check Red Hat CVE and errata pages for product-specific fixed package versions.
  • Reduce unnecessary remote graphical service exposure while vendor updates are being applied.

Validation and detection

  • Inventory installed xorg-x11-server, xorg-x11-server-Xwayland, and tigervnc package versions on Red Hat systems.
  • Compare installed packages against the affected versions listed in the CVE bundle.
  • Confirm applicable RHSA advisories have been applied for each supported RHEL lifecycle stream.
  • Document any RHEL 6 xorg-x11-server findings separately because its status is unknown here.
Prepared
Confidence
high
Sources
12

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.

ATT&CK lookup starting points

Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.

cwe · low confidence lookup

CWE-787: Exact CWE lookup

Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.

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cve · low confidence lookup

CVE-2023-6816 mapping review

Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.

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Vulnerability profileCVE Program record
Severity
Critical
CVSS
9.8 (3.1)
Known Exploited
No
Published

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

Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

1CVSS vectors
0Timeline events
0ADP providers
24Source links

CVSS vector scores

1 official score

We collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.

ScoreVersionSeverityVectorExploitImpactSource
9.8CVSS 3.1CriticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H3.95.9Primary CVE score

Vulnerability scoring details

Base CVSS 3.1 score

9.8Critical
CVSS 3.1 vector shape for CVE-2023-6816Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

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

Attack Vector
NetworkAdjacentLocalPhysical
Attack Complexity
LowHigh
Privileges Required
NoneLowHigh
User Interaction
NoneRequired
Scope
ChangedUnchanged
Confidentiality Impact
HighLowNone
Integrity Impact
HighLowNone
Availability Impact
HighLowNone

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
Red HatRed Hat Enterprise Linux 6 Extended Lifecycle Support - EXTENSIONtigervnc, 0:1.1.0-25.el6_10.13affected
Red HatRed Hat Enterprise Linux 7xorg-x11-server, 0:1.20.4-27.el7_9affected
Red HatRed Hat Enterprise Linux 7tigervnc, 0:1.8.0-31.el7_9affected
Red HatRed Hat Enterprise Linux 8tigervnc, 0:1.13.1-2.el8_9.7affected
Red HatRed Hat Enterprise Linux 8xorg-x11-server, 0:1.20.11-22.el8affected
Red HatRed Hat Enterprise Linux 8xorg-x11-server-Xwayland, 0:21.1.3-15.el8affected
Red HatRed Hat Enterprise Linux 8.2 Advanced Update Supporttigervnc, 0:1.9.0-15.el8_2.9affected
Red HatRed Hat Enterprise Linux 8.2 Telecommunications Update Servicetigervnc, 0:1.9.0-15.el8_2.9affected
Red HatRed Hat Enterprise Linux 8.2 Update Services for SAP Solutionstigervnc, 0:1.9.0-15.el8_2.9affected
Red HatRed Hat Enterprise Linux 8.4 Advanced Mission Critical Update Supporttigervnc, 0:1.11.0-8.el8_4.8affected
Red HatRed Hat Enterprise Linux 8.4 Telecommunications Update Servicetigervnc, 0:1.11.0-8.el8_4.8affected
Red HatRed Hat Enterprise Linux 8.4 Update Services for SAP Solutionstigervnc, 0:1.11.0-8.el8_4.8affected
Red HatRed Hat Enterprise Linux 8.6 Extended Update Supporttigervnc, 0:1.12.0-6.el8_6.9affected
Red HatRed Hat Enterprise Linux 8.8 Extended Update Supporttigervnc, 0:1.12.0-15.el8_8.7affected
Red HatRed Hat Enterprise Linux 9tigervnc, 0:1.13.1-3.el9_3.6affected
Red HatRed Hat Enterprise Linux 9xorg-x11-server, 0:1.20.11-24.el9affected
Red HatRed Hat Enterprise Linux 9xorg-x11-server-Xwayland, 0:22.1.9-5.el9affected
Red HatRed Hat Enterprise Linux 9.0 Extended Update Supporttigervnc, 0:1.11.0-22.el9_0.8affected
Red HatRed Hat Enterprise Linux 9.2 Extended Update Supporttigervnc, 0:1.12.0-14.el9_2.5affected
Red HatRed Hat Enterprise Linux 6xorg-x11-serverunknown
Weakness

CWE details

CWE-787

CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.