# CVE-2026-93518: X.org X server integer truncation in XkbResizeKeyType heap buffer overflow

Source: https://junglewise.ai/threats/cve-2026-93518-an-integer-truncation-issue-in-xkbresizekeytype-that-could-lead  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-10-28. Updated: 2026-10-28  
License: CC BY 4.0 with a link back

CVE-2026-93518 · Severity: high · CVSS 7.8 · Published 2026-10-28

The X.org X server is a critical component that manages graphical display output for Unix and Linux systems. An integer truncation bug in its keyboard handling allows authenticated X clients to trigger a heap buffer overflow, leading to server crashes or potentially arbitrary code execution with X server privileges. This affects systems running unpatched X servers or XWayland.

Technologies: [X.Org X Server](https://junglewise.ai/threats/technologies/x-org-x-server), [X.Org XWayland](https://junglewise.ai/threats/technologies/x-org-xwayland). Vendors: [X.Org](https://junglewise.ai/threats/vendors/x-org).

## Quick answers

**Is CVE-2026-93518 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-93518 being exploited in the wild.

**How severe is CVE-2026-93518?** High severity, with a CVSS score of 7.8, published 28 October 2026.

**Which products and versions are affected?** X.Org X Server before 21.1.25; X.Org XWayland before 24.1.14.

**Is there a fix for CVE-2026-93518?** Yes: fixed in X server 21.1.25; XWayland 24.1.14. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-93518 attacked?** It is attacked over the network or with local access.

**Am I affected by CVE-2026-93518?** Check whether you run X.Org X Server or X.Org XWayland at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- Fixed in X server 21.1.25; XWayland 24.1.14

## Technical details

An integer truncation vulnerability exists in XkbResizeKeyType() where size_syms and num_syms fields are declared as 16-bit unsigned shorts but computed values are truncated when assigned. When XkbResizeKeyType() calculates (nTotal * 15) / 10, the 32-bit result is implicitly truncated to 16 bits, causing undersized memory allocation followed by out-of-bounds writes. Authenticated X clients can exploit this via XKB SetMap requests to achieve heap buffer overflow.

## Affected products

- X.org X server before 21.1.25
- X.org XWayland before 24.1.14

## Timeline

- 2026-10-28: disclosed
- 2026-08-26: patched: Commit 89101a6c widened fields from unsigned short to unsigned int

## References

- [https://gitlab.freedesktop.org/xorg/xserver/-/commit/89101a6c6618f543d7502f2077c7ef1a507af256](https://gitlab.freedesktop.org/xorg/xserver/-/commit/89101a6c6618f543d7502f2077c7ef1a507af256)

## Related threats

- [X.Org X Server use after free in gesture sprite lifecycle](https://junglewise.ai/threats/cve-2026-93536-a-use-after-free-caused-by-missing-lifecycle-management-of)
- [X.Org X Server buffer overread in CheckKeySyms](https://junglewise.ai/threats/cve-2026-93524-a-buffer-overread-in-checkkeysyms-in-x-org-x-server-before-21-1)
- [X.Org X Server heap buffer overflow in XIPassiveUngrabDevice](https://junglewise.ai/threats/cve-2026-93523-a-heap-buffer-overflow-caused-by-a-xipassiveungrabdevice-request)
- [X.Org X Server heap buffer overflow in CopyArea CPU-to-FBO](https://junglewise.ai/threats/cve-2026-93522-a-heap-buffer-overflow-caused-by-mismatched-size-usage-in)
- [X.Org X Server buffer overflow in RandR ChangeProviderProperty](https://junglewise.ai/threats/cve-2026-93521-a-buffer-overflow-in-randr-changeproviderproperty-requests-in-x)