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CVE Record

CVE-2026-50261: Xorg-x11-server: xorg-x11-server-xwayland: xorg-x11-server: use-after-free in syncchangecounter()

A use-after-free flaw was found in the X.Org X server and Xwayland in SyncChangeCounter(). A client that sets up multiple SyncCounters can trigger a use-after-free when destroying those counters via a second client connection while changing those counters. This may be used to crash the server, or for privilege escalation if the X server runs as root.

HighCVSS 7.8Not KEV-listedUpdated
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Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

A logged-in or otherwise locally permitted user could abuse X.Org or Xwayland memory handling to crash the graphical server. If that server runs as root, the flaw may also allow the user to gain elevated privileges, threatening system availability and control.

Executive priority

Treat as a high-priority local privilege-escalation and availability issue. Accelerate remediation on shared workstations, administrative systems, VDI or VNC hosts, and servers running graphical components as root. Broader deployment can follow normal high-severity patch timelines after exposure is verified.

Technical view

CVE-2026-50261 is a CWE-416 use-after-free in SyncChangeCounter(). Multiple SyncCounters manipulated through separate client connections can leave freed memory in use. The CVSS 3.1 score is 7.8: local access and low privileges are required, but successful exploitation could compromise confidentiality, integrity, and availability without user interaction.

Likely exposure

Exposure includes the listed Red Hat Enterprise Linux 7 ELS, RHEL 8 and supported 8.x add-ons, and RHEL 10/EUS systems running affected xorg-x11-server, xorg-x11-server-Xwayland, or tigervnc builds. Risk is greatest where untrusted local users or VNC sessions can connect to an active X server, particularly one running as root.

Exploitation context

The supplied record does not identify this CVE as KEV and provides no evidence of active exploitation. Exploitation requires local, low-privileged client access. Confirmed outcomes are server crash and potential privilege escalation when the X server runs as root; reliability and real-world weaponization are not established by the supplied sources.

Researcher notes

The affected mechanism involves cross-connection lifetime handling of SyncCounters in SyncChangeCounter(). Assessment should focus on package provenance, active graphical services, client trust boundaries, and server privileges. The bundle lists affected Red Hat builds and advisories but does not supply upstream patch details, fixed-version comparisons, exploit reliability, or forensic indicators.

Mitigation direction

  • Apply the applicable Red Hat security erratum updates for each installed RHEL stream and affected package.
  • Prioritize systems where X.Org, Xwayland, or TigerVNC runs as root or serves multiple users.
  • Restrict untrusted local and remote graphical-session access until applicable updates are installed.
  • Check current Red Hat guidance for stream-specific fixed package versions and restart requirements.

Validation and detection

  • Inventory installed xorg-x11-server, xorg-x11-server-Xwayland, and tigervnc package versions across affected RHEL systems.
  • Compare each package version and RHEL support stream with the applicable Red Hat erratum.
  • Identify active X.Org, Xwayland, and TigerVNC services and determine their runtime privileges.
  • After updating, confirm affected packages were replaced and required services or systems were restarted.
  • Review graphical-server crashes or abnormal terminations, while recognizing they do not prove exploitation.
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

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cwe · low confidence lookup

CWE-416: 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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description · low confidence lookup

Privilege behavior lookup

The CVE wording references privilege impact, so privilege escalation and authorization behavior review may help. This is a Glexia inferred lookup path, not an official MITRE, ATT&CK, or CVE Program mapping.

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cve · low confidence lookup

CVE-2026-50261 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
34Source 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-2026-50261Attack 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. ADP timelineredhat-SADP

    Reported to Red Hat.

  2. Source timelineredhat

    Reported to Red Hat.

  3. ADP timelineredhat-SADP

    Made public.

  4. Source timelineredhat

    Made public.

  5. CVE reservedCVE Program

    The CVE ID was reserved by the assigning CNA.

  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-x11-server: xorg-x11-server-Xwayland: xorg-x11-server: use-after-free in SyncChangeCounter()
other:Red Hat severity ratingcvssV3_1
  • 2026-05-15T03:14:46.000Z: Reported to Red Hat.
  • 2026-06-02T00:00:00.000Z: Made public.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
Red HatRed Hat Enterprise Linux 10xorg-x11-server-Xwayland, 0:24.1.9-4.el10_2.2affected
Red HatRed Hat Enterprise Linux 10.0 Extended Update Supportxorg-x11-server-Xwayland, 0:24.1.5-6.el10_0.1affected
Red HatRed Hat Enterprise Linux 7 Extended Lifecycle Supportxorg-x11-server, 0:1.20.4-35.el7_9affected
Red HatRed Hat Enterprise Linux 7 Extended Lifecycle Supporttigervnc, 0:1.8.0-36.el7_9.5affected
Red HatRed Hat Enterprise Linux 8xorg-x11-server-Xwayland, 0:21.1.3-20.el8_10.2affected
Red HatRed Hat Enterprise Linux 8xorg-x11-server, 0:1.20.11-28.el8_10.2affected
Red HatRed Hat Enterprise Linux 8tigervnc, 0:1.15.0-10.el8_10affected
Red HatRed Hat Enterprise Linux 8.4 Advanced Mission Critical Update Supportxorg-x11-server, 0:1.20.10-5.el8_4affected
Red HatRed Hat Enterprise Linux 8.4 Advanced Mission Critical Update Supporttigervnc, 0:1.11.0-8.el8_4.16affected
Red HatRed Hat Enterprise Linux 8.4 Extended Update Support Long-Life Add-Onxorg-x11-server, 0:1.20.10-5.el8_4affected
Red HatRed Hat Enterprise Linux 8.4 Extended Update Support Long-Life Add-Ontigervnc, 0:1.11.0-8.el8_4.16affected
Red HatRed Hat Enterprise Linux 8.6 Advanced Mission Critical Update Supportxorg-x11-server, 0:1.20.11-8.el8_6affected
Red HatRed Hat Enterprise Linux 8.6 Advanced Mission Critical Update Supportxorg-x11-server-Xwayland, 0:21.1.3-2.el8_6.7affected
Red HatRed Hat Enterprise Linux 8.6 Advanced Mission Critical Update Supporttigervnc, 0:1.12.0-6.el8_6.18affected
Red HatRed Hat Enterprise Linux 8.6 Extended Update Support Long-Life Add-Onxorg-x11-server, 0:1.20.11-8.el8_6affected
Red HatRed Hat Enterprise Linux 8.6 Extended Update Support Long-Life Add-Onxorg-x11-server-Xwayland, 0:21.1.3-2.el8_6.7affected
Red HatRed Hat Enterprise Linux 8.6 Extended Update Support Long-Life Add-Ontigervnc, 0:1.12.0-6.el8_6.18affected
Red HatRed Hat Enterprise Linux 8.8 Telecommunications Update Servicexorg-x11-server, 0:1.20.11-19.el8_8affected
Red HatRed Hat Enterprise Linux 8.8 Telecommunications Update Servicexorg-x11-server-Xwayland, 0:21.1.3-13.el8_8.1affected
Red HatRed Hat Enterprise Linux 8.8 Telecommunications Update Servicetigervnc, 0:1.12.0-15.el8_8.18affected
Red HatRed Hat Enterprise Linux 8.8 Update Services for SAP Solutionsxorg-x11-server, 0:1.20.11-19.el8_8affected
Red HatRed Hat Enterprise Linux 8.8 Update Services for SAP Solutionsxorg-x11-server-Xwayland, 0:21.1.3-13.el8_8.1affected
Red HatRed Hat Enterprise Linux 8.8 Update Services for SAP Solutionstigervnc, 0:1.12.0-15.el8_8.18affected
Red HatRed Hat Enterprise Linux 9xorg-x11-server-Xwayland, 0:24.1.9-4.el9_8.2affected
Red HatRed Hat Enterprise Linux 9xorg-x11-server, 0:1.20.11-34.el9_8.2affected
Red HatRed Hat Enterprise Linux 9tigervnc, 0:1.15.0-7.el9_8.2affected
Red HatRed Hat Enterprise Linux 9.2 Update Services for SAP Solutionsxorg-x11-server, 0:1.20.11-21.el9_2affected
Red HatRed Hat Enterprise Linux 9.2 Update Services for SAP Solutionsxorg-x11-server-Xwayland, 0:21.1.3-10.el9_2.1affected
Red HatRed Hat Enterprise Linux 9.2 Update Services for SAP Solutionstigervnc, 0:1.12.0-14.el9_2.15affected
Red HatRed Hat Enterprise Linux 9.4 Update Services for SAP Solutionsxorg-x11-server, 0:1.20.11-29.el9_4affected
Weakness

CWE details

CWE-416

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

CWE-416 · source CWE mapping

Use After Free

Use After Free represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.

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