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CVE Record

CVE-2025-26595: Xorg: xwayland: buffer overflow in xkbvmodmasktext()

A buffer overflow flaw was found in X.Org and Xwayland. The code in XkbVModMaskText() allocates a fixed-sized buffer on the stack and copies the names of the virtual modifiers to that buffer. The code fails to check the bounds of the buffer and would copy the data regardless of the size.

HighCVSS 7.8Not KEV-listedUpdated
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Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

CVE-2025-26595 is a high-severity memory safety flaw in X.Org/Xwayland code used by graphical Linux environments. A local authenticated user could potentially crash the service or gain high-impact access on affected systems. Exposure is most relevant on systems providing local desktops, Xwayland sessions, or VNC-based graphical access.

Executive priority

Prioritize patching where Linux graphical access supports administrators, developers, jump hosts, or VNC users. This is not described as remotely exploitable from the network, but a successful local attack could have full confidentiality, integrity, and availability impact on affected hosts.

Technical view

XkbVModMaskText() uses a fixed-size stack buffer and copies virtual modifier names without bounds checks, creating a CWE-121 stack-based buffer overflow. The CVSS 3.1 vector is local, low complexity, low privileges, no user interaction, with high confidentiality, integrity, and availability impact.

Likely exposure

The source bundle lists affected Red Hat xorg-x11-server, xorg-x11-server-Xwayland, and tigervnc packages across RHEL 6 ELS, 7 ELS, 8, 9, 10, and selected AUS/EUS/E4S/TUS streams. Non-Red Hat xserver 22.0.0 exposure is noted, but vendor coverage is incomplete.

Exploitation context

The record supports local exploitation only: attack vector is local and privileges are required. The bundle says KEV is false and provides no cited evidence of active exploitation. Treat internet-facing VNC or shared desktop infrastructure as higher operational priority because local access may be easier to obtain there.

Researcher notes

Evidence identifies the vulnerable function and package families, but the bundle does not include exploit proof, weaponization details, or fixed package version mapping beyond RHSA references. Focus validation on package provenance, advisory applicability, and whether Xwayland, X.Org server, or TigerVNC code paths are installed and reachable.

Mitigation direction

  • Apply the relevant Red Hat RHSA updates for affected xorg-x11-server, Xwayland, and tigervnc packages.
  • Check upstream or distribution vendor guidance for non-Red Hat X.Org, Xwayland, or xserver builds.
  • Prioritize multi-user desktops, jump hosts, VNC servers, and systems running untrusted local workloads.
  • Limit local shell and remote graphical access until affected packages are updated.
  • Monitor Red Hat CVE and errata pages for revised affected-package or fix information.

Validation and detection

  • Inventory installed xorg-x11-server, xorg-x11-server-Xwayland, tigervnc, and xserver package versions.
  • Map operating system streams against the affected Red Hat product list in the source bundle.
  • Confirm the applicable RHSA advisory has been applied through approved patch management evidence.
  • Validate graphical login, Xwayland application launch, and VNC workflows after patching.
  • Record exceptions where vendor guidance is unavailable or systems are outside listed Red Hat streams.
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-121: 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-2025-26595 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.

1CVSS vectors
5Timeline events
2ADP providers
19Source links

SSVC decision data

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

CVSS vector scores

1 official score

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

Vulnerability scoring details

Base CVSS 3.1 score

7.8High
CVSS 3.1 vector shape for CVE-2025-26595Attack 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. Source timelineredhat

    Reported to Red Hat.

  3. Source timelineredhat

    Made public.

  4. CVE publishedCVE Program

    The CVE record was published.

  5. CVE updatedCVE Program

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

ADP provider summaries

CISA-ADPCISA ADP Vulnrichment
other:ssvc
CVECVE Program Container

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
Unknown vendorxserverxserver, 0, 22.0.0unaffected
Red HatRed Hat Enterprise Linux 10xorg-x11-server-Xwayland, 0:24.1.5-3.el10_0affected
Red HatRed Hat Enterprise Linux 6 Extended Lifecycle Support - EXTENSIONtigervnc, 0:1.1.0-25.el6_10affected
Red HatRed Hat Enterprise Linux 7 Extended Lifecycle Supporttigervnc, 0:1.8.0-36.el7_9affected
Red HatRed Hat Enterprise Linux 7 Extended Lifecycle Supportxorg-x11-server, 0:1.20.4-30.el7_9affected
Red HatRed Hat Enterprise Linux 8tigervnc, 0:1.13.1-15.el8_10affected
Red HatRed Hat Enterprise Linux 8.2 Advanced Update Supporttigervnc, 0:1.9.0-15.el8_2.13affected
Red HatRed Hat Enterprise Linux 8.4 Advanced Mission Critical Update Supporttigervnc, 0:1.11.0-8.el8_4.12affected
Red HatRed Hat Enterprise Linux 8.4 Telecommunications Update Servicetigervnc, 0:1.11.0-8.el8_4.12affected
Red HatRed Hat Enterprise Linux 8.4 Update Services for SAP Solutionstigervnc, 0:1.11.0-8.el8_4.12affected
Red HatRed Hat Enterprise Linux 8.6 Advanced Mission Critical Update Supporttigervnc, 0:1.12.0-6.el8_6.13affected
Red HatRed Hat Enterprise Linux 8.6 Telecommunications Update Servicetigervnc, 0:1.12.0-6.el8_6.13affected
Red HatRed Hat Enterprise Linux 8.6 Update Services for SAP Solutionstigervnc, 0:1.12.0-6.el8_6.13affected
Red HatRed Hat Enterprise Linux 8.8 Extended Update Supporttigervnc, 0:1.12.0-15.el8_8.12affected
Red HatRed Hat Enterprise Linux 9tigervnc, 0:1.14.1-1.el9_5.1affected
Red HatRed Hat Enterprise Linux 9xorg-x11-server, 0:1.20.11-28.el9_6affected
Red HatRed Hat Enterprise Linux 9xorg-x11-server-Xwayland, 0:23.2.7-3.el9_6affected
Red HatRed Hat Enterprise Linux 9.0 Update Services for SAP Solutionstigervnc, 0:1.11.0-22.el9_0.13affected
Red HatRed Hat Enterprise Linux 9.2 Extended Update Supporttigervnc, 0:1.12.0-14.el9_2.10affected
Red HatRed Hat Enterprise Linux 9.4 Extended Update Supporttigervnc, 0:1.13.1-8.el9_4.5affected
Red HatRed Hat Enterprise Linux 6xorg-x11-serverunknown
Red HatRed Hat Enterprise Linux 8xorg-x11-serverunaffected
Red HatRed Hat Enterprise Linux 8xorg-x11-server-Xwaylandunaffected
Weakness

CWE details

CWE-121

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

CWE-121 · source CWE mapping

Stack-based Buffer Overflow

Stack-based Buffer Overflow represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.

Open CWE intelligenceSame-CWE CVEs