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CVE Record

CVE-2026-33999: Xorg: xwayland: x.org x server: denial of service via integer underflow in xkb compatibility map handling

A flaw was found in the X.Org X server. This integer underflow vulnerability, specifically in the XKB compatibility map handling, allows an attacker with local or remote X11 server access to trigger a buffer read overrun. This can lead to memory-safety violations and potentially a denial of service (DoS) or other severe impacts.

HighCVSS 7.8Not KEV-listedUpdated
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Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

This flaw affects X.Org/Xwayland handling of keyboard compatibility data. An attacker who already has local or remote access to an X11 server could trigger memory-safety errors, potentially crashing display services and, per the CVSS impact ratings, risking broader confidentiality, integrity, and availability impact.

Executive priority

Treat as high priority for Linux desktop, VDI, VNC, and administrative jump-host environments. The business concern is disruption or memory-safety impact in graphical access services, especially where many users share display infrastructure.

Technical view

CVE-2026-33999 is a CWE-191 integer underflow in XKB compatibility map handling. The source bundle says it can cause a buffer read overrun in X.Org X server components, including Xwayland and related Red Hat xorg-x11-server and tigervnc packages. CVSS is 7.8, AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H.

Likely exposure

Exposure is most likely on affected Red Hat Enterprise Linux systems running listed xorg-x11-server, xorg-x11-server-Xwayland, or tigervnc packages. Risk is higher on multi-user desktops, VNC environments, or systems allowing remote X11 server access.

Exploitation context

The bundle does not show CISA KEV listing and provides no evidence of active exploitation. Attackers need access to the X11 server context, so this is not described as unauthenticated internet exploitation. Public technical detail is limited in the provided sources.

Researcher notes

The key constraint is attacker access to the X11 server. Focus triage on reachable X11/VNC surfaces and package lineage. The provided material does not include proof-of-concept details, exploit telemetry, or precise fixed package versions beyond Red Hat advisory references.

Mitigation direction

  • Review the applicable Red Hat RHSA advisory for each affected RHEL stream.
  • Apply vendor-provided updates for xorg-x11-server, Xwayland, or tigervnc where applicable.
  • Restrict remote X11 and VNC access to trusted users and networks.
  • Prioritize shared graphical systems and remote desktop hosts before single-user workstations.

Validation and detection

  • Inventory installed xorg-x11-server, xorg-x11-server-Xwayland, and tigervnc package versions.
  • Map each host to its RHEL major, minor, EUS, AUS, TUS, or ELS channel.
  • Compare installed package builds against the affected versions in the CVE bundle.
  • Confirm applicable Red Hat errata are installed through standard package management records.
  • Check whether remote X11 or VNC access is enabled on exposed systems.
Prepared
Confidence
medium
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-191: 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-2026-33999 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
High
CVSS
7.8 (3.1)
Known Exploited
No
Published

Vector: CVSS:3.1/AV:L/AC:L/PR:L/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.

2CVSS vectors
7Timeline events
2ADP providers
39Source links

SSVC decision data

CISA-ADPCISA Coordinator
Timestamp
Version
2.0.3
Exploitation: noneAutomatable: noTechnical Impact: total

CVSS vector scores

2 official scores

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
7.8CVSS 3.1HighCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H1.85.9redhat
7.8CVSS 3.1HighCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H1.85.9redhat-SADP

Vulnerability scoring details

Base CVSS 3.1 score

7.8High
CVSS 3.1 vector shape for CVE-2026-33999Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

Vector: CVSS:3.1/AV:L/AC:L/PR:L/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

Vulnerability timeline

Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.

  1. CVE reservedCVE Program

    The CVE ID was reserved by the assigning CNA.

  2. ADP timelineredhat-SADP

    Reported to Red Hat.

  3. Source timelineredhat

    Reported to Red Hat.

  4. ADP timelineredhat-SADP

    Made public.

  5. Source timelineredhat

    Made public.

  6. CVE publishedCVE Program

    The CVE record was published.

  7. CVE updatedCVE Program

    The CVE record metadata indicates this as the latest update time.

ADP provider summaries

CISA-ADPCISA ADP Vulnrichment
other:ssvc
redhat-SADPxorg: xwayland: X.Org X server: Denial of Service via integer underflow in XKB compatibility map handling
other:Red Hat severity ratingcvssV3_1
  • 2026-03-25T06:29:19.544Z: Reported to Red Hat.
  • 2026-04-23T14:11:12.550Z: Made public.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
Red HatRed Hat Enterprise Linux 10xorg-x11-server-Xwayland, 0:24.1.5-6.el10_1affected
Red HatRed Hat Enterprise Linux 10xorg-x11-server-Xwayland, 0:24.1.9-4.el10_2affected
Red HatRed Hat Enterprise Linux 10.0 Extended Update Supportxorg-x11-server-Xwayland, 0:24.1.5-6.el10_0affected
Red HatRed Hat Enterprise Linux 6 Extended Lifecycle Support - EXTENSIONtigervnc, 0:1.1.0-25.el6_10.16affected
Red HatRed Hat Enterprise Linux 7 Extended Lifecycle Supportxorg-x11-server, 0:1.20.4-34.el7_9affected
Red HatRed Hat Enterprise Linux 7 Extended Lifecycle Supporttigervnc, 0:1.8.0-36.el7_9.4affected
Red HatRed Hat Enterprise Linux 8xorg-x11-server-Xwayland, 0:21.1.3-20.el8_10affected
Red HatRed Hat Enterprise Linux 8xorg-x11-server, 0:1.20.11-28.el8_10affected
Red HatRed Hat Enterprise Linux 8tigervnc, 0:1.15.0-9.el8_10affected
Red HatRed Hat Enterprise Linux 8.4 Advanced Mission Critical Update Supportxorg-x11-server, 0:1.20.10-4.el8_4affected
Red HatRed Hat Enterprise Linux 8.4 Advanced Mission Critical Update Supporttigervnc, 0:1.11.0-8.el8_4.15affected
Red HatRed Hat Enterprise Linux 8.4 Extended Update Support Long-Life Add-Onxorg-x11-server, 0:1.20.10-4.el8_4affected
Red HatRed Hat Enterprise Linux 8.4 Extended Update Support Long-Life Add-Ontigervnc, 0:1.11.0-8.el8_4.15affected
Red HatRed Hat Enterprise Linux 8.6 Advanced Mission Critical Update Supportxorg-x11-server-Xwayland, 0:21.1.3-2.el8_6.6affected
Red HatRed Hat Enterprise Linux 8.6 Advanced Mission Critical Update Supportxorg-x11-server, 0:1.20.11-7.el8_6affected
Red HatRed Hat Enterprise Linux 8.6 Advanced Mission Critical Update Supporttigervnc, 0:1.12.0-6.el8_6.17affected
Red HatRed Hat Enterprise Linux 8.6 Extended Update Support Long-Life Add-Ontigervnc, 0:1.12.0-6.el8_6.17affected
Red HatRed Hat Enterprise Linux 8.6 Telecommunications Update Servicexorg-x11-server-Xwayland, 0:21.1.3-2.el8_6.6affected
Red HatRed Hat Enterprise Linux 8.6 Telecommunications Update Servicexorg-x11-server, 0:1.20.11-7.el8_6affected
Red HatRed Hat Enterprise Linux 8.6 Update Services for SAP Solutionsxorg-x11-server-Xwayland, 0:21.1.3-2.el8_6.6affected
Red HatRed Hat Enterprise Linux 8.6 Update Services for SAP Solutionsxorg-x11-server, 0:1.20.11-7.el8_6affected
Red HatRed Hat Enterprise Linux 8.8 Telecommunications Update Servicexorg-x11-server-Xwayland, 0:21.1.3-13.el8_8affected
Red HatRed Hat Enterprise Linux 8.8 Telecommunications Update Servicexorg-x11-server, 0:1.20.11-18.el8_8affected
Red HatRed Hat Enterprise Linux 8.8 Telecommunications Update Servicetigervnc, 0:1.12.0-15.el8_8.17affected
Red HatRed Hat Enterprise Linux 8.8 Update Services for SAP Solutionsxorg-x11-server-Xwayland, 0:21.1.3-13.el8_8affected
Red HatRed Hat Enterprise Linux 8.8 Update Services for SAP Solutionsxorg-x11-server, 0:1.20.11-18.el8_8affected
Red HatRed Hat Enterprise Linux 8.8 Update Services for SAP Solutionstigervnc, 0:1.12.0-15.el8_8.17affected
Red HatRed Hat Enterprise Linux 9tigervnc, 0:1.15.0-6.el9_7.1affected
Red HatRed Hat Enterprise Linux 9xorg-x11-server-Xwayland, 0:23.2.7-6.el9_7affected
Red HatRed Hat Enterprise Linux 9xorg-x11-server, 0:1.20.11-33.el9_7affected
Weakness

CWE details

CWE-191

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

CWE-191 · source CWE mapping

Integer Underflow (Wrap or Wraparound)

Integer Underflow (Wrap or Wraparound) represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.

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