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Attack ChainAIDerived

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

  1. Access
    Open connection to X11 display
  2. Delivery
    Issue XSYNC fence create/trigger requests
  3. Exploit
    Trigger use-after-free in miSyncTriggerFence()
  4. Execution
    Corrupt X server heap memory
  5. Persist
    Crash server or execute in server context
  6. Impact
    Denial of service or privilege escalation

Vulnerability Assessment

Weakness
CWE
CWE-825
ASVS 5.0
V15 - Secure Coding and Architecture Expired pointer prevention
Exploitation Conditions

Exploitation requires the attacker to have a client connection to a running X.Org X server and the ability to issue XSYNC extension requests (creating and triggering a fence), which reaches the vulnerable miSyncTriggerFence() path; no user interaction is needed. The primary limiting factor is reachability of the display: by default the server only accepts local clients (Unix socket, '-nolisten tcp'), so an attacker needs a local session or, where remote X (TCP display or X forwarding) is explicitly enabled, a forwarded client connection. Per CVSS PR:L the attacker must be an authenticated low-privileged user able to open the display rather than fully unauthenticated; the XSYNC extension must be present and active, which it is in standard desktop builds.
Impact

The CVSS 3.1 vector (AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H) describes a low-complexity, locally-reachable flaw requiring only low privileges (a client able to open the X11 display) and no user interaction, with high impact to confidentiality, integrity, and availability - consistent with SSVC's 'Technical Impact: total'. However, SSVC also records 'Exploitation: none' and 'Automatable: no', and EPSS is only 0.01% (3rd percentile), indicating no observed exploitation and low near-term probability. These signals align rather than conflict: the flaw is genuinely serious for local privilege escalation on multi-user or sandbox-escape scenarios, but it is not a mass-exploited remote issue. The realistic priority is moderate - patch on a normal maintenance cadence, prioritizing shared or multi-user X hosts. Note the reachability nuance: 'access to the X11 server' can extend to remote clients where TCP display access or X forwarding is enabled, which would effectively broaden the vector beyond pure local.
Exploit ScenarioDerived

A local user (or a remote user whose session can reach the display) writes a malicious X11 client that manipulates XSYNC fences to trigger miSyncTriggerFence() against a freed object, corrupting the server's heap. Because AC is low and no user interaction is needed, the client can repeatedly attempt the condition to crash the display (denial of service) or groom the heap toward controllable corruption. No public exploit is identified at time of analysis, so this remains a plausible rather than demonstrated attack.
This Week Schedule remediation this week. Why: HIGH severity (CVSS 7.0-8.9).
Patch available 0.0% exploitation probability (EPSS)

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AnalysisAIv1 – Jul 24, 2026

Local privilege-relevant memory corruption in the X.Org X server arises from a use-after-free in the XSYNC fence-triggering path (miSyncTriggerFence()), letting any client with a connection to the display crash the server or corrupt heap memory without user interaction. Rated CVSS 7.8 with total technical impact per CISA SSVC, it currently shows no public exploit identified at time of analysis, no CISA KEV listing, and a very low EPSS of 0.01% (3rd percentile). Because the X server frequently runs with elevated privileges, successful memory corruption could escalate beyond denial of service.

RemediationAI

Patch available per vendor advisory: apply the updated xorg-x11-server packages from your distribution. Red Hat users should install the fixes delivered in RHSA-2026:10739, RHSA-2026:11352, and RHSA-2026:11369 (https://access.redhat.com/errata/RHSA-2026:10739); SUSE users should apply the corresponding SUSE-SU-2026:1328 through 1335 or SUSE-SU-2026:21211 updates (https://www.suse.com/support/update/SUSE-SU-2026:1328/), then restart the display server or reboot so the running server picks up the fix. As a compensating control until patching, restrict who can connect to the X server: disable X11 TCP listening (run with '-nolisten tcp', the modern default) and avoid enabling remote X forwarding for untrusted users to shrink the set of clients that can reach the vulnerable XSYNC path; on shared hosts, limit local interactive/SSH access to trusted accounts. These controls reduce exposure but do not eliminate risk for legitimate local users, and disabling X forwarding may break remote GUI workflows that rely on it.

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Technical ContextAI · show details

The X.Org X server is the reference implementation of the X11 display server that mediates between graphical clients and input/output hardware on Linux and Unix desktops. The XSYNC extension provides synchronization primitives (counters and fences) that clients use to coordinate rendering; the miSyncTriggerFence() routine in the machine-independent (mi) sync layer fires callbacks when a fence is triggered. The defect is classified CWE-825 (Expired Pointer Dereference), a use-after-free variant: the fence trigger logic dereferences a pointer to an object that has already been freed, so attacker-influenced heap contents can be interpreted as valid server structures, producing a crash or controllable memory corruption within the server process.

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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
vuln.today AI 7.8 HIGH

A low-privileged local client can reach the XSYNC path with low complexity and no interaction; use-after-free in the privileged server yields high C/I/A within an unchanged scope.

3.1 AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
4.0 AV:L/AC:L/AT:N/PR:L/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N
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

Lifecycle Timeline

2
Patch released
Apr 28, 2026 - 20:30 nvd
Patch available
CVE Published
Apr 23, 2026 - 14:54 nvd
HIGH 7.8

DescriptionCVE.org

A flaw was found in the X.Org X server. This use-after-free vulnerability occurs in the XSYNC fence triggering logic, specifically within the miSyncTriggerFence() function. An attacker with access to the X11 server can exploit this without user interaction, leading to a server crash and potentially enabling memory corruption. This could result in a denial of service or further compromise of the system.

Zero Day Initiative Advisories

ZDI-26-335 X.Org Server SyncAwaitFence Use-After-Free Privilege Escalation Vulnerability Jun 2026

Executive ViewAI

Why It Matters

A critical vulnerability in X.Org X server (CVE-2026-34001) could enable local users to crash systems or escalate their privileges. This affects any organization running X.Org display servers where users have local system access. No public exploit identified at time of analysis; however, vendor patch is available and should be deployed promptly to minimize risk exposure.

Business Impact: High
Compensating Controls

Apply vendor patch.

Threat Intelligence Overview

EPSS Score
0.0%
Top 97% exploitable
Prevalence
Ubiquitous
X.Org server underlies most Linux/Unix graphical desktops
Social Media
5
Sightings
Data Quality
7 sources
Confidence: High
EUVD NVD CVE.org EPSS Vulnrichment MSRC Vendor CIRCL 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 Yes
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

Buffer Overflow HIGH

A buffer overflow occurs when a program writes more data to a memory buffer than it was allocated to hold, causing the excess data to spill into adjacent memory regions.

Denial of Service MEDIUM

Denial of Service attacks render applications or systems unavailable by overwhelming resources or triggering failure conditions.

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_6:*:*:*:*:*:*:*:*
cpe:2.3:a:red_hat:red_hat_enterprise_linux_7:*:*:*:*:*:*:*:*
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_8:*:*:*:*:*:*:*:*
cpe:2.3:a:red_hat:red_hat_enterprise_linux_9:*:*:*:*:*:*:*:*
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-825 – Expired Pointer Dereference

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Vendor StatusVendor

SUSE

Severity: High
Product Status
Image SLES15-SP4-SAP Image SLES15-SP4-SAP-Azure Image SLES15-SP4-SAP-EC2 Image SLES15-SP4-SAP-GCE Image SLES15-SP4-SAPCAL Image SLES15-SP4-SAPCAL-Azure Image SLES15-SP4-SAPCAL-EC2 Image SLES15-SP4-SAPCAL-GCE Affected
Image SLES15-SP5-SAPCAL-Azure Image SLES15-SP5-SAPCAL-GCE Affected
Image SLES15-SP6-SAP Image SLES15-SP6-SAP-EC2 Image SLES15-SP6-SAPCAL Image SLES15-SP6-SAPCAL-EC2 Affected
SUSE Liberty Linux 9 Fixed
SUSE Linux Enterprise Desktop 15 SP7 SUSE Linux Enterprise Server 15 SP7 SUSE Linux Enterprise Server for SAP Applications 15 SP7 Fixed

References

Advisories & patches
ADVISORY https://nvd.nist.gov/vuln/detail/CVE-2026-34001 ADVISORY https://vuldb.com/vuln/359149 ADVISORY https://www.suse.com/support/update/SUSE-SU-2026:1328/ ADVISORY https://www.suse.com/support/update/SUSE-SU-2026:1329/ ADVISORY https://www.suse.com/support/update/SUSE-SU-2026:1330/ ADVISORY https://www.suse.com/support/update/SUSE-SU-2026:1331/ ADVISORY https://www.suse.com/support/update/SUSE-SU-2026:1332/ ADVISORY https://www.suse.com/support/update/SUSE-SU-2026:1333/ ADVISORY https://www.suse.com/support/update/SUSE-SU-2026:1335/ ADVISORY https://www.suse.com/support/update/SUSE-SU-2026:21211/ REF https://access.redhat.com/errata/RHSA-2026:10739 REF https://access.redhat.com/errata/RHSA-2026:11352 REF https://access.redhat.com/errata/RHSA-2026:11369 REF https://access.redhat.com/errata/RHSA-2026:11388 REF https://access.redhat.com/errata/RHSA-2026:11656 REF https://access.redhat.com/errata/RHSA-2026:11692 REF https://access.redhat.com/errata/RHSA-2026:13414 REF https://access.redhat.com/errata/RHSA-2026:19125 REF https://access.redhat.com/errata/RHSA-2026:19342 REF https://access.redhat.com/errata/RHSA-2026:19343 REF https://access.redhat.com/errata/RHSA-2026:19344 REF https://access.redhat.com/errata/RHSA-2026:20547 REF https://access.redhat.com/errata/RHSA-2026:20555 REF https://access.redhat.com/errata/RHSA-2026:20557 REF https://access.redhat.com/errata/RHSA-2026:20558 REF https://access.redhat.com/errata/RHSA-2026:20560 REF https://access.redhat.com/errata/RHSA-2026:20561 REF https://access.redhat.com/errata/RHSA-2026:20562 REF https://access.redhat.com/errata/RHSA-2026:20563 REF https://access.redhat.com/errata/RHSA-2026:20575 REF https://access.redhat.com/errata/RHSA-2026:20576 REF https://access.redhat.com/errata/RHSA-2026:20590 REF https://access.redhat.com/errata/RHSA-2026:21699 REF https://access.redhat.com/errata/RHSA-2026:21712 REF https://access.redhat.com/errata/RHSA-2026:21715 REF https://access.redhat.com/errata/RHSA-2026:21716 REF https://access.redhat.com/errata/RHSA-2026:21718 REF https://access.redhat.com/errata/RHSA-2026:21741 REF https://access.redhat.com/errata/RHSA-2026:21742 REF https://access.redhat.com/errata/RHSA-2026:22424 REF https://access.redhat.com/errata/RHSA-2026:22456 REF https://access.redhat.com/errata/RHSA-2026:23254 REF https://access.redhat.com/errata/RHSA-2026:23255 REF https://access.redhat.com/errata/RHSA-2026:23496 REF https://access.redhat.com/errata/RHSA-2026:24341 REF https://access.redhat.com/security/cve/CVE-2026-34001 REF https://bugzilla.redhat.com/show_bug.cgi?id=2451109 REF https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-34001.json

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