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Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata – not a confirmed exploit chain

  1. Recon
    Obtain local user shell on RHEL host
  2. Delivery
    Open two X client connections with valid auth
  3. Exploit
    Create multiple SyncCounters with pending triggers
  4. Install
    Destroy counters via second connection to trigger FreeCounter() UAF
  5. C2
    Groom heap to control freed SyncCounter memory
  6. Execute
    Hijack control flow in X server process
  7. Impact
    Execute code as root (or session user on Xwayland)

Vulnerability Assessment

Weakness
CWE
CWE-416
ASVS 5.0
V15 - Secure Coding and Architecture Memory lifecycle management
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.

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Exploitation Conditions

Exploitation requires the attacker to already have local authenticated access to an active X server endpoint (either a classic Xorg display socket or an Xwayland instance) and the ability to open at least two concurrent client connections to that server with valid X authorization cookies. The attacker must drive the XSync extension to create multiple SyncCounter objects with active triggers/awaits, then destroy those counters from the second connection to reach FreeCounter() in the freed state. Maximum impact (root privilege escalation) is gated on the X server running as root - typical of legacy Xorg sessions, display-manager-spawned servers, and some kiosk/remote-X setups; on default modern Wayland desktops where Xwayland runs as the unprivileged user, impact is limited to that user's session. No network reachability and no user interaction are required (AV:L/UI:N), but PR:L means a non-privileged local account is a hard prerequisite.
Impact

The CVSS 3.1 vector AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H yields a base score of 7.8 (High), reflecting local attack vector, low complexity, low privileges (authenticated local user), no user interaction, and full CIA impact. Real-world risk is meaningfully elevated on systems where the X server still runs as root (traditional Xorg sessions, kiosks, some remote-X setups), where successful exploitation yields root; on modern Wayland-default desktops where Xwayland runs unprivileged, impact is reduced to a session crash or compromise of that user's display. There is no EPSS score provided, no KEV listing, and no public POC referenced, so this is currently a defensible high-severity local issue rather than a mass-exploitation priority. The Red Hat advisory and upstream xorg-announce posting confirm the bug is genuine; however, exact fixed package NVRs were not provided in the input and must be confirmed via the Red Hat errata system.
Exploit ScenarioDerived

A local authenticated attacker (for example, a low-privileged shell user on a multi-user RHEL workstation or a malicious app within a desktop session) opens two client connections to the X server, registers multiple SyncCounters with pending triggers on the first connection, and uses the second connection to destroy those counters, triggering the FreeCounter() use-after-free. Through heap grooming the attacker shapes the freed memory to gain code execution in the X server's address space, which yields root privileges on systems where Xorg still runs as root or session-level compromise where Xwayland runs unprivileged. No public exploit identified at time of analysis, but use-after-free bugs in xserver have a track record of being weaponized.
This Week Schedule remediation this week. Why: HIGH severity (CVSS 7.0-8.9).
No patch listed yet 0.0% exploitation probability (EPSS)

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AnalysisAIv1 – Jun 05, 2026

Local privilege escalation in the X.Org X server and Xwayland arises from a use-after-free in FreeCounter() when SyncCounter objects are destroyed across multiple client connections. Authenticated local attackers on affected Red Hat Enterprise Linux 6 through 10 systems can crash the server or escalate to root when the X server runs with elevated privileges. No public exploit identified at time of analysis, and the issue is not listed in CISA KEV.

RemediationAI

Upstream fix available (commit f5abfb61994471023d8c6470428c8e30c411cc0b at https://gitlab.freedesktop.org/xorg/xserver/-/commit/f5abfb61994471023d8c6470428c8e30c411cc0b); a released patched version was not independently confirmed in the supplied data, so administrators should apply Red Hat errata referenced from https://access.redhat.com/security/cve/CVE-2026-50260 once they list specific xorg-x11-server and xorg-x11-server-Xwayland package versions. As compensating controls until patched packages are deployed, prefer Wayland sessions where Xwayland runs unprivileged rather than legacy Xorg-as-root sessions (trade-off: legacy X11-only apps requiring root X features may break), restrict local interactive logins on multi-user systems via PAM/access.conf to reduce the pool of authenticated attackers (trade-off: operational friction), and where possible disable the XSync extension or block untrusted clients from connecting to the server socket using xhost/Xauthority hardening (trade-off: applications relying on XSync alarms such as some compositors and animation toolkits will degrade or fail).

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Technical ContextAI · show details

The vulnerability resides in the XSync extension of the X.Org X server (xserver) and its Wayland-compatibility component Xwayland, both maintained at gitlab.freedesktop.org/xorg/xserver. SyncCounters are server-side objects exposed by the XSync protocol extension that allow clients to coordinate timing via shared counter values and triggers (alarms). The root cause is CWE-416 (Use-After-Free): when one client allocates multiple SyncCounters with pending triggers and a second client connection causes FreeCounter() to release those counters, dangling references to the freed counter memory remain reachable, allowing subsequent operations to dereference or write to freed heap memory. Exploitation primitives from use-after-free in C-based servers like xserver typically allow attacker-controlled function pointer overwrite or heap layout manipulation leading to arbitrary code execution.

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Severity by source

Vendor (redhat) PRIMARY 7.8 HIGH
AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
SUSE HIGH
Red Hat 7.8 HIGH

Primary rating from Vendor (redhat).

CVSS VectorVendor: redhat

Attack Vector
Local
Attack Complexity
Low
Privileges Required
Low
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

DescriptionCVE.org

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

Zero Day Initiative Advisories

ZDI-26-394 X.Org Server FreeCounter Use-After-Free Privilege Escalation Vulnerability Jun 2026

Executive ViewAI

Why It Matters

A local privilege escalation vulnerability in X.Org X server and Xwayland (CVE-2026-50260) enables authenticated users to escalate to root on RHEL 6 through 10 systems, directly threatening organizations with Linux desktop or workstation deployments. Any system running X.Org with elevated privileges is exposed, making this a material security risk for environments where local user access exists.

Business Impact: High
Compensating Controls

No vendor-released patch identified at time of analysis. Interim mitigations: (1) Uninstall X.Org/Xwayland packages where not essential; (2) Restrict X server execution via sudo configuration and privilege boundary controls; (3) Disable X11 forwarding and network X11 access via SSH configuration; (4) Implement filesystem and RBAC controls to limit X server process execution to administrators; (5) Monitor system logs for unexpected privilege escalation events and X server crashes.

Threat Intelligence Overview

EPSS Score
0.0%
Top 98% exploitable
Data Quality
7 sources
Confidence: High
EUVD NVD CVE.org EPSS Vulnrichment MSRC Vendor VulDB

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 HIGH
CISA KEV No
Public POC No
EPSS 0.0%
Patch available No
Active threat No
Deciding rule
HIGH severity (CVSS 7.0-8.9)
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
Scheduled
Exploitation
None
System Exposure· derived
Small
Automatable
No
Human Impact
High
Technical Impact
Total

Priority Score

39
Low Medium High Critical
KEV: 0
EPSS: 0
CVSS: +39
PoC: 0
Weaponized: 0
Threat intel: 0
Gov advisory: 0

Attack Technique

Privilege Escalation HIGH

Privilege escalation occurs when an attacker leverages flaws in access control mechanisms to gain permissions beyond what they were originally granted.

Use After Free HIGH

Use-after-free vulnerabilities occur when a program continues to access memory through a pointer after that memory has been deallocated.

Memory Corruption HIGH

Memory corruption occurs when a program writes data beyond the boundaries of allocated memory regions or accesses memory in unintended ways, violating the integrity of the process's address space.

Affected Products (CPE)CVE.org

cpe:2.3:a:red_hat:red_hat_enterprise_linux_10:*:*:*:*:*:*:*:*
cpe:2.3:a:red_hat:red_hat_enterprise_linux_6:*:*:*:*:*:*:*:*
cpe:2.3:a:red_hat:red_hat_enterprise_linux_7:*:*:*:*:*:*:*:*
cpe:2.3:a:red_hat:red_hat_enterprise_linux_8:*:*:*:*:*:*:*:*
cpe:2.3:a:red_hat:red_hat_enterprise_linux_8:*:*:*:*:*:*:*:*
cpe:2.3:a:red_hat:red_hat_enterprise_linux_9:*:*:*:*:*:*:*:*
cpe:2.3:a:red_hat:red_hat_enterprise_linux_9:*:*:*:*:*:*:*:*

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Same weakness CWE-416 – Use After Free

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Same technique Privilege Escalation

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Vendor StatusVendor

SUSE

Severity: Important
Product Status
SUSE Linux Enterprise Desktop 15 SP7 Affected
SUSE Linux Enterprise Desktop 15 SP7 Affected
SUSE Linux Enterprise High Performance Computing 15 SP7 Affected
SUSE Linux Enterprise Module for Basesystem 15 SP7 Affected
SUSE Linux Enterprise Module for Development Tools 15 SP7 Affected

References

Advisories & patches
ADVISORY https://nvd.nist.gov/vuln/detail/CVE-2026-50260 ADVISORY https://vuldb.com/vuln/368895 REF https://access.redhat.com/errata/RHSA-2026:26562 REF https://access.redhat.com/errata/RHSA-2026:26566 REF https://access.redhat.com/errata/RHSA-2026:26590 REF https://access.redhat.com/errata/RHSA-2026:26610 REF https://access.redhat.com/errata/RHSA-2026:26709 REF https://access.redhat.com/errata/RHSA-2026:28923 REF https://access.redhat.com/errata/RHSA-2026:29844 REF https://access.redhat.com/errata/RHSA-2026:36083 REF https://access.redhat.com/errata/RHSA-2026:36085 REF https://access.redhat.com/errata/RHSA-2026:36086 REF https://access.redhat.com/errata/RHSA-2026:36087 REF https://access.redhat.com/errata/RHSA-2026:36632 REF https://access.redhat.com/errata/RHSA-2026:36633 REF https://access.redhat.com/errata/RHSA-2026:36634 REF https://access.redhat.com/errata/RHSA-2026:36768 REF https://access.redhat.com/errata/RHSA-2026:36791 REF https://access.redhat.com/errata/RHSA-2026:36792 REF https://access.redhat.com/errata/RHSA-2026:36798 REF https://access.redhat.com/errata/RHSA-2026:38502 REF https://access.redhat.com/errata/RHSA-2026:38810 REF https://access.redhat.com/errata/RHSA-2026:46377 REF https://access.redhat.com/errata/RHSA-2026:46382 REF https://access.redhat.com/errata/RHSA-2026:46385 REF https://access.redhat.com/errata/RHSA-2026:46392 REF https://access.redhat.com/errata/RHSA-2026:46456 REF https://access.redhat.com/errata/RHSA-2026:46460 REF https://access.redhat.com/errata/RHSA-2026:46473 REF https://access.redhat.com/errata/RHSA-2026:49519 REF https://access.redhat.com/security/cve/CVE-2026-50260 REF https://bugzilla.redhat.com/show_bug.cgi?id=2485385 REF https://gitlab.freedesktop.org/xorg/xserver/-/commit/f5abfb61994471023d8c6470428c8e30c411cc0b REF https://lists.x.org/archives/xorg-announce/2026-June/003702.html REF https://redhat.atlassian.net/browse/PSIRTSUPT-16950 REF https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-50260.json

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