---
id: "CVE-2026-98900"
kind: "vulnerability"
aliases: ["CVE-2026-98900"]
title: "Linux kernel: Xen grant allocation checks count too late, risking overflow"
severity: "unknown"
cvss: null
epss: 0.00215
exploited: false
status: "open"
category: "infrastructure"
products: []
ecosystems: []
tags: ["infrastructure", "linux-kernel", "xen"]
not_affected_if: ["no-gntalloc-device", "no-xen"]
published_at: "2026-10-23T12:18:24+00:00"
first_seen_at: "2026-10-23T21:57:33+00:00"
updated_at: "2026-10-25T12:38:50+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-98900", "first_seen_at": "2026-10-23T21:57:33+00:00"}, {"source": "epss", "url": "https://api.first.org/data/v1/epss?cve=CVE-2026-98900", "first_seen_at": "2026-10-25T12:38:50+00:00"}]
---

# Linux kernel: Xen grant allocation checks count too late, risking overflow

The Linux kernel's Xen grant-table allocator allocated a user-sized array before checking the count against the global limit, and the limit check could wrap. The fix rejects oversized counts earlier and does the page-size math in 64-bit, which blocks memory-exhaustion or overflow abuse from the ioctl path.

_Summary, check and fix written by a model from the sources; labelled as such._

## Timeline

- 2026-10-23T21:57:33+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-98900
- 2026-10-25T12:38:50+00:00 epss https://api.first.org/data/v1/epss?cve=CVE-2026-98900

## From the sources

In the Linux kernel, the following vulnerability has been resolved:

xen/gntalloc: validate grant count before allocation

gntalloc_ioctl_alloc() allocates the grant-id array before checking
whether the requested count fits within the global grant limit. Counts
above that limit cannot succeed, so reject them before the
user-controlled allocation reaches kcalloc().

Use a subtraction-based check while holding gref_mutex so adding the
requested count cannot wrap. Also cast the count before advancing the
per-file index so the page-size multiplication is performed in 64-bit
arithmetic.

---

_Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_