Xorg-x11-server: xorg-x11-server-xwayland: xorg-x11-server: stack buffer overflow in xkb setmap request via mapwidths indexing (CVE-2026-50259)

Xorg-x11-server: xorg-x11-server-xwayland: xorg-x11-server: stack buffer overflow in xkb setmap request via mapwidths indexing (CVE-2026-50259) | HOL Guard CVE

Why this deserves its current priority

CVSS is 7.8. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.

Analysis status

Analysis pending evidence review

Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.

Affected scope and exposure questions

Affected software not mapped in the current feed; confirm the named product and version against your inventory.

Affected products and reported versions
Product	Affected versions	Fixed versions
cpe:2.3:a:x.org:x_server::::::::	Not reported	Not reported
cpe:2.3:a:x.org:xwayland::::::::	Not reported	Not reported
cpe:2.3:o:redhat:enterprise_linux:10.0:::::::*	Not reported	Not reported
cpe:2.3:o:redhat:enterprise_linux:7.0:::::::*	Not reported	Not reported
cpe:2.3:o:redhat:enterprise_linux:8.0:::::::*	Not reported	Not reported
cpe:2.3:o:redhat:enterprise_linux:9.0:::::::*	Not reported	Not reported

Recommended response

Confirm exposure. Identify whether the named product or interface exists in your inventory, then review the linked upstream references for affected versions and vendor guidance.

Evidence timeline and material changes

Published upstream
Jun 5, 2026
Evidence: source:cvelist:source_dates:source-dates:record
Source modified
Aug 5, 2026
Evidence: source:cvelist:source_dates:source-dates:record
First seen by HOL
Jun 22, 2026

Sources and claim methodology

Upstream source description

A stack-based buffer overflow flaw was found in the X.Org X server and Xwayland. _XkbSetMapChecks() declares a fixed-size stack buffer mapWidths[256] indexed by key type index. The helper function CheckKeyTypes() writes to this buffer at a client-controlled offset, allowing a stack buffer overflow. This may be used to crash the server, or for privilege escalation if the X server runs as root.

Quoted source text, attributed separately from HOL analysis.