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Full vulnerability report · 2026
CVE-2026-50256High confidence

Xorg-x11-server: xorg-x11-server-xwayland: xorg-x11-server: stack buffer overflow in font alias resolution due to libxfont2 name length mismatch

Red Hat · Red Hat Enterprise Linux 10

Official source article: Red Hat RHSA-2026:26562 ↗. Check the applicable product and release in the original source.

7.8HighCVSS 3.1
Recommended action
Patch only the product branches with a verified fix

High technical severity; prioritise exposed affected systems while verifying vendor guidance. Verified remediation exists for at least one product or source, but 2 structured product or package states remain unresolved. Apply remediation only to the exact product branch confirmed by its source.

Fix availability varies by product
R
Operational reassessment

Published severity in operational context

Open reassessment dashboard →
Published severityHighOperational priority:Medium, lowered one band.downgradedsince 28 Sep 2026

Evidence used

  • No CISA KEV confirmation is currently recorded.
  • Exploitation requires an existing local or physical foothold with privileges.
  • EPSS is 0.21% for the current model date.

Compensating controls

  • Validate the affected product branch and deploy the verified fixed release.
  • Restrict local access and enforce least privilege on affected hosts.
  • Monitor vendor guidance and exploitation sources for a material change.

Verification

  1. Confirm that the asset runs Red Hat Red Hat Enterprise Linux 10 and falls inside the recorded affected range.
  2. Verify the installed build against the product-specific fixed version after deployment.
  3. Validate exposure, authentication requirements and compensating controls in the actual environment.
  4. Reopen this reassessment when CVSS, KEV, EPSS, exploit evidence or remediation changes.
Mitigation target: As exposure requiresRemediation target: Within 365 days

This automated reassessment organises public evidence. It does not know asset exposure, business impact or control effectiveness and does not replace CVSS or a human risk decision.

Cross-source reconciliation

Remediation availability differs by product scope

Verified remediation exists for at least one product or source, but 2 structured product or package states remain unresolved. Apply remediation only to the exact product branch confirmed by its source.

Distribution package intelligence

Release-specific package status

Debian, ubuntu findings are scoped to the named distribution, release and source package. An absent finding does not mean a package is unaffected.

10 package states
Package result overrides the generic status

BlackTree has verified remediation for at least one product or source, but the relevant distribution still reports no fixed package for 2 affected package states shown here. Treat those rows as affected with no fix until that distribution publishes a fixed version.

Repository candidate not checked

A published vendor fix does not prove that a matching update is enabled and installable on a particular asset. Confirm the local package candidate before scheduling remediation.

Distribution releaseSource packageVendor stateFixed versionEvidence
Debian trixietrixie · sourcexorg-serverVendor fix publishedDebian records a fixed source-package version for this release.2:21.1.16-1.3+deb13u3Debian Security Tracker ↗Source updated 5 Oct 2026
Debian trixietrixie · sourcexwaylandAffected, no fix publishedDebian currently tracks this release as open.Not published in this feedDebian Security Tracker ↗Source updated 5 Oct 2026
Debian bookwormbookworm · sourcexorg-serverVendor fix publishedDebian records a fixed source-package version for this release.2:21.1.7-3+deb12u13Debian Security Tracker ↗Source updated 5 Oct 2026
Debian bookwormbookworm · sourcexwaylandAffected, no fix publishedDebian currently tracks this release as open.Not published in this feedDebian Security Tracker ↗Source updated 5 Oct 2026
Debian forkyforky · sourcexorg-serverVendor fix publishedDebian records a fixed source-package version for this release.2:21.1.23-1Debian Security Tracker ↗Source updated 5 Oct 2026
Debian forkyforky · sourcexwaylandVendor fix publishedDebian records a fixed source-package version for this release.2:24.1.12-1Debian Security Tracker ↗Source updated 5 Oct 2026
Debian sidsid · sourcexorg-serverVendor fix publishedDebian records a fixed source-package version for this release.2:21.1.23-1Debian Security Tracker ↗Source updated 5 Oct 2026
Debian sidsid · sourcexwaylandVendor fix publishedDebian records a fixed source-package version for this release.2:24.1.12-1Debian Security Tracker ↗Source updated 5 Oct 2026
Ubuntu 24.04 LTSnoble · standard archivexorg-serverUnder evaluationCanonical reports that the package might be affected and still needs evaluation or fixing.Not published in this feedCanonical Ubuntu Security ↗Source updated 5 Oct 2026
Ubuntu 24.04 LTSnoble · standard archivexwaylandUnder evaluationCanonical reports that the package might be affected and still needs evaluation or fixing.Not published in this feedCanonical Ubuntu Security ↗Source updated 5 Oct 2026
Direct vendor intelligence

Authoritative vendor CSAF and VEX advisories

Structured product status and remediation from the issuing vendor. Product-state explanations are always visible; large lists can be searched or downloaded.

1 current
CVE-2026-50256 · CSAF 2.0 · revision 3 · finalRed Hat Product Securityxorg-x11-server: xorg-x11-server-Xwayland: xorg-x11-server: stack buffer overflow in font alias resolution due to libXfont2 name length mismatch
9 known affected

The vendor explicitly identifies these products as affected by this CVE.

  • xorg-x11-server-Xdmx as a component of Red Hat Enterprise Linux 6
  • xorg-x11-server-Xephyr as a component of Red Hat Enterprise Linux 6
  • xorg-x11-server-Xnest as a component of Red Hat Enterprise Linux 6
  • xorg-x11-server-Xorg as a component of Red Hat Enterprise Linux 6
  • xorg-x11-server-Xvfb as a component of Red Hat Enterprise Linux 6
  • xorg-x11-server-common as a component of Red Hat Enterprise Linux 6
  • xorg-x11-server-devel as a component of Red Hat Enterprise Linux 6
  • xorg-x11-server-source as a component of Red Hat Enterprise Linux 6
  • xorg-x11-server.src as a component of Red Hat Enterprise Linux 6
Summary
A stack-based buffer overflow flaw was found in the X.Org X server and Xwayland. A mismatch between the X server and the libXfont2 library's maximum font name length can cause a stack buffer overflow during font alias resolution. The server allocates a 256 byte stack buffer but libXfont2's alias target name length is 1024 bytes. A font alias name between 257 and 1023 bytes causes the X server to copy that name into the undersized stack buffer without further checks. This may be used to crash the server, or for privilege escalation if the X server runs as root.
Remediation
For details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258
Optional official sources

National CERT insights
?CERT means Computer Emergency Response Team; CSIRT is the closely related term Computer Security Incident Response Team.

Choose official national sources for this report. Each advisory shows its original language. Your selection is remembered on this device and included in shared links.

Official European source

ENISA European Vulnerability Database

Official EUVD identifiers, advisory evidence and known-exploited context. Missing fields are not treated as evidence of low risk.

1 current
ENISA EUVD identifier

EUVD-2026-34813

No EUVD known-exploited evidence

A stack-based buffer overflow flaw was found in the X.Org X server and Xwayland. A mismatch between the X server and the libXfont2 library's maximum font name length can cause a stack buffer overflow during font alias resolution. The server allocates a 256 byte stack buffer but libXfont2's alias target name length is 1024 bytes. A font alias name between 257 and 1023 bytes causes the X server to copy that name into the undersized stack buffer without further checks. This may be used to crash the server, or for privilege escalation if the X server runs as root.

EUVD state
Present in the current official mapping
Known exploitation
Not present in the current ENISA EUVD known-exploited dataset. This is not proof of no exploitation.
ENISA score
7.8 · CVSS 3.1
Advisory evidence
No linked advisory details stored yet
Recommended actionPatch only the product branches with a verified fix

High technical severity; prioritise exposed affected systems while verifying vendor guidance. Verified remediation exists for at least one product or source, but 2 structured product or package states remain unresolved. Apply remediation only to the exact product branch confirmed by its source.

Fix availability varies by product
01

What, why and how

A stack-based buffer overflow flaw was found in the X.Org X server and Xwayland. A mismatch between the X server and the libXfont2 library's maximum font name length can cause a stack buffer overflow during font alias resolution. The server allocates a 256 byte stack buffer but libXfont2's alias target name length is 1024 bytes. A font alias name between 257 and 1023 bytes causes the X server to copy that name into the undersized stack buffer without further checks. This may be used to crash the server, or for privilege escalation if the X server runs as root.

What

A stack-based buffer overflow flaw was found in the X.Org X server and Xwayland. A mismatch between the X server and the libXfont2 library's maximum font name length can cause a stack buffer overflow during font alias resolution. The server allocates a 256 byte stack buffer but libXfont2's alias target name length is 1024 bytes. A font alias name between 257 and 1023 bytes causes the X server to copy that name into the undersized stack buffer without further checks. This may be used to crash the server, or for privilege escalation if the X server runs as root.

Why

A stack-based buffer overflow condition is a condition where the buffer being overwritten is allocated on the stack (i.e., is a local variable or, rarely, a parameter to a function).

How

An attacker operating through local access may attempt exploitation with low privileges. If successful, the issue may gain additional privileges.

What

A stack-based buffer overflow flaw was found in the X.Org X server and Xwayland. A mismatch between the X server and the libXfont2 library's maximum font name length can cause a stack buffer overflow during font alias resolution. The server allocates a 256 byte stack buffer but libXfont2's alias target name length is 1024 bytes. A font alias name between 257 and 1023 bytes causes the X server to copy that name into the undersized stack buffer without further checks. This may be used to crash the server, or for privilege escalation if the X server runs as root.

Why

A stack-based buffer overflow condition is a condition where the buffer being overwritten is allocated on the stack (i.e., is a local variable or, rarely, a parameter to a function).

How

An attacker operating through local access may attempt exploitation with low privileges. If successful, the issue may gain additional privileges.

02

Exploit reality and attack path

CVSS severity, EPSS forecast probability, public exploit material and CISA-confirmed exploitation are separate signals.

Observed exploitation
?Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.
No confirmed evidence

No CISA KEV match was present at the last successful refresh. This means no confirmation from that source, not proof of no exploitation.

Public PoC / exploit material
?Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.
None recorded

No exploit-tagged reference or CISA SSVC proof-of-concept state is currently recorded. Research may still exist outside the structured feeds.

Likely attack path
local access → Stack-based Buffer Overflow → gain additional privileges
Attack surface
Local
Privileges required
Low: a basic authenticated account is required
User interaction
None
Attack complexity
Low: no specialised conditions are recorded
Security boundary
Unchanged: impact remains within the vulnerable component's security authority
Weakness
?CWE means Common Weakness Enumeration: a standard category for the underlying weakness.
CWE-121 ↗

CWE-121: Stack-based Buffer Overflow. A stack-based buffer overflow condition is a condition where the buffer being overwritten is allocated on the stack (i.e., is a local variable or, rarely, a parameter to a function).

CVSS vector
?CVSS means Common Vulnerability Scoring System. The vector records the metric values used to calculate technical severity.
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Common Vulnerability Scoring System 3.1: the compact vector below is decoded into plain language.

AVLocalAttack vector: The attacker needs local access to the vulnerable system.ACLowAttack complexity: No specialised conditions are required beyond attacker-controlled input.PRLowPrivileges required: The attacker needs basic user-level privileges.UINoneUser interaction: No action by another user is required.SUnchangedScope: The security impact remains within the vulnerable component's authority.CHighConfidentiality impact: A successful attack can cause a major loss.IHighIntegrity impact: A successful attack can cause a major loss.AHighAvailability impact: A successful attack can cause a major loss.
Post-exploitation / living off the land
The issue can support a local privilege or sandbox boundary transition; normal system utilities may then be available in the gained context.
Privilege escalationDenial of serviceCWE-121
A

Official authority intelligence

Only matched European and national findings are included. Language selectors and unavailable sources are omitted.

ENISA EUVD · EUVD-2026-34813Official EUVD mapping

A stack-based buffer overflow flaw was found in the X.Org X server and Xwayland. A mismatch between the X server and the libXfont2 library's maximum font name length can cause a stack buffer overflow during font alias resolution. The server allocates a 256 byte stack buffer but libXfont2's alias target name length is 1024 bytes. A font alias name between 257 and 1023 bytes causes the X server to copy that name into the undersized stack buffer without further checks. This may be used to crash the server, or for privilege escalation if the X server runs as root.

Official EUVD record ↗
BSI · German · WID-SEC-2026-2455Oracle Solaris Drittanbieterkomponenten: Mehrere Schwachstellen

Ein entfernter, anonymer oder authentisierter Angreifer kann mehrere Schwachstellen in verschiedenen Komponenten von Drittanbietern in Oracle Solaris ausnutzen, um einen nicht näher spezifizierten Angriff durchzuführen.

Official advisory ↗
BSI · German · WID-SEC-2026-1774X.Org X11 und Xwayland: Mehrere Schwachstellen

Ein Angreifer kann mehrere Schwachstellen in X.Org X11 und Xwayland ausnutzen, um Informationen offenzulegen, um seine Privilegien zu erhöhen, um einen Denial of Service Angriff durchzuführen, und um einen nicht näher spezifizierten Angriff durchzuführen.

Official advisory ↗
Cyber Security Agency of Singapore · English · CSA-SB-20260610Security Bulletin 10 Jun 2026

The Cyber Security Agency of Singapore included this CVE in its official Security Bulletin 10 Jun 2026, published on 10 June 2026. Open the linked bulletin for the product, severity and reference information published in that issue.

Official advisory ↗
CERT-FR · French · CERTFR-2026-AVI-0737Multiples vulnérabilités dans les produits Microsoft

De multiples vulnérabilités ont été découvertes dans les produits Microsoft. Elles permettent à un attaquant de provoquer un problème de sécurité non spécifié par l'éditeur.

Official advisory ↗
JVN iPedia · Japanese · JVNDB-2026-018740レッドハット等の複数ベンダの製品におけるスタックベースのバッファオーバーフローの脆弱性

X.Org XサーバーおよびXwaylandにスタックベースのバッファオーバーフローの脆弱性が発見されました。XサーバーとlibXfont2ライブラリの最大フォント名長の不一致により、フォントエイリアス解決時にスタックバッファオーバーフローが発生する可能性があります。サーバーは256バイトのスタックバッファを割り当てますが、libXfont2のエイリアスターゲット名の長さは1024バイトです。257バイトから1023バイトの間のフォントエイリアス名が存在すると、Xサーバーは追加のチェックなしにその名前をサイズ不足のスタックバッファにコピーします。これにより、サーバーがクラッシュしたり、Xサーバーがrootとして実行されている場合に権限昇格を招く可能性があります。

Official advisory ↗
03

Patch and workaround

Operational remediation based on structured source evidence.

Status
?Patch availability is based on structured fixed-version fields and authoritative update references. If no fix is verified, check the vendor advisory before making a change.
Fix availability varies by product
Affected
Fixed
Action
Use the product-specific evidence above. Patch only products with a verified fixed release, and keep every affected or under-investigation state without a matching fix in the remediation queue.
Workaround
No verified workaround is recorded. Limit untrusted access and use least privilege until authoritative guidance is available.
04

Evidence and provenance

Published 5 Jun 2026 · Last source change 28 Sept 2026, 11:45 UTC · CWE-121 · Stack-based Buffer Overflow

CVE recordCVE.org · 5.2
CVSS sourceCNA
EPSS source
?The date BlackTree first stored a score for this CVE from the daily FIRST EPSS feed.
FIRST · tracked since 2026-08-14
European sourceENISA EUVD · EUVD-2026-34813
Product sourceVendor CSAF · Red Hat Product Security
Remediation sourceVendor CSAF · Red Hat Product Security
CWE sourceCNA
NVD statusNVD modified after enrichment

Core structured fields are present and their contributing authorities are shown above.

Material change intelligence

What changed after publication

View recent updates ↗
  1. Affected versionsThe structured affected or fixed version information changed.
    Before
    See the vendor and CVE records for the affected range. · Fixed: 0:24.1.9-4.el10_2.2 < *; 0:24.1.5-6.el10_0.1 < *; 0:1.1.0-25.el6_10.18 < *; 0:1.20.4-35.el7_9 < *; 0:1.8.0-36.el7_9.5 < *; 0:21.1.3-20.el8_10.2 < *; 0:1.20.11-28.el8_10.2 < *; 0:1.15.0-10.el8_10 < *
    After
    See the vendor and CVE records for the affected range. · Fixed: Red Hat Enterprise Linux 10: 0:24.1.9-4.el10_2.2 < *; Red Hat Enterprise Linux 10.0 Extended Update Support: 0:24.1.5-6.el10_0.1 < *; Red Hat Enterprise Linux 6 Extended Lifecycle Support - EXTENSION: 0:1.1.0-25.el6_10.18 < *; Red Hat Enterprise Linux 7 Extended Lifecycle Support: 0:1.20.4-35.el7_9 < *, 0:1.8.0-36.el7_9.5 < *; Red Hat Enterprise Linux 8: 0:21.1.3-20.el8_10.2 < *, 0:1.20.11-28.el8_10.2 < *, 0:1.15.0-10.el8_10 < *; Red Hat Enterprise Linux 8.4 Advanced Mission Critical Update Support: 0:1.20.10-5.el8_4 < *, 0:1.11.0-8.el8_4.16 < *; Red Hat Enterprise Linux 8.4 Extended Update Support Long-Life Add-On: 0:1.20.10-5.el8_4 < *, 0:1.11.0-8.el8_4.16 < *; Red Hat Enterprise Linux 8.6 Advanced Mission Critical Update Support: 0:1.20.11-8.el8_6 < *, 0:21.1.3-2.el8_6.7 < *, 0:1.12.0-6.el8_6.18 < *; Red Hat Enterprise Linux 8.6 Extended Update Support Long-Life Add-On: 0:1.20.11-8.el8_6 < *, 0:21.1.3-2.el8_6.7 < *, 0:1.12.0-6.el8_6.18 < *; Red Hat Enterprise Linux 8.8 Telecommunications Update Service: 0:1.20.11-19.el8_8 < *, 0:21.1.3-13.el8_8.1 < *, 0:1.12.0-15.el8_8.18 < *; Red Hat Enterprise Linux 8.8 Update Services for SAP Solutions: 0:1.20.11-19.el8_8 < *, 0:21.1.3-13.el8_8.1 < *, 0:1.12.0-15.el8_8.18 < *; Red Hat Enterprise Linux 9: 0:24.1.9-4.el9_8.2 < *, 0:1.20.11-34.el9_8.2 < *, 0:1.15.0-7.el9_8.2 < *; Red Hat Enterprise Linux 9.2 Update Services for SAP Solutions: 0:1.20.11-21.el9_2 < *, 0:21.1.3-10.el9_2.1 < *, 0:1.12.0-14.el9_2.15 < *; Red Hat Enterprise Linux 9.4 Update Services for SAP Solutions: 0:1.20.11-29.el9_4 < *, 0:22.1.9-8.el9_4.1 < *, 0:1.13.1-8.el9_4.10 < *; Red Hat Enterprise Linux 9.6 Extended Update Support: 0:1.20.11-34.el9_6 < *, 0:23.2.7-6.el9_6.1 < *, 0:1.14.1-11.el9_6 < *
    CNA ↗
Material fields only · duplicate refreshes suppressed · history retained for the configured operational retention period
CVE published
Fixed release or patch reference recorded
ENISA EUVD · EUVD-2026-34813↗Vendor advisory↗Vendor advisory↗Patch or update reference↗CVE authority or vendor reference · Red Hat RHSA-2026:26562↗Official CVE record (CNA and ADP data)↗NVD record↗
Technical terms and abbreviations used in this report
CVE
Common Vulnerabilities and Exposures: the public identifier for one disclosed vulnerability.
CVSS
Common Vulnerability Scoring System: a technical severity framework; it is not patching priority by itself.
EPSS
Exploit Prediction Scoring System: FIRST's estimate of the probability that exploitation activity will be observed in the next 30 days; it is a forecast, not confirmation.
CWE
Common Weakness Enumeration: the standard category describing the underlying software or hardware weakness.
CNA
CVE Numbering Authority: an organisation authorised to assign and publish CVE records.
CISA ADP
Cybersecurity and Infrastructure Security Agency Authorized Data Publisher: structured enrichment added to a CVE record.
NVD
National Vulnerability Database: NIST's enrichment service for CVE records.
CERT / CSIRT
A computer security incident response team that publishes warnings or coordinates incident response.
PoC
Proof of concept: public material that demonstrates or helps reproduce exploitation.
CSAF
Common Security Advisory Framework: a machine-readable format for security advisories.
LoTL
Living off the land: abuse of legitimate tools or system functions during an attack.
Free version - for non-commercial use only.CVE-2026-50256 · cve.blacktree.nl