CVE-2025-68171 (GCVE-0-2025-68171)
Vulnerability from cvelistv5 – Published: 2025-12-16 13:42 – Updated: 2026-08-05 12:09
VLAI
EPSS
VEX
Title
x86/fpu: Ensure XFD state on signal delivery
Summary
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 ]
Severity
7.8 (High)
Assigner
References
Impacted products
2 products
| Vendor | Product | Version | CPE status | |
|---|---|---|---|---|
| Linux | Linux |
Affected:
672365477ae8afca5a1cca98c1deb733235e4525 , < eefbfb722042fc9210d2e0ac2b063fd1abf51895
(git)
Affected: 672365477ae8afca5a1cca98c1deb733235e4525 , < 1811c610653c0cd21cc9add14595b7cffaeca511 (git) Affected: 672365477ae8afca5a1cca98c1deb733235e4525 , < 5b2619b488f1d08b960c43c6468dd0759e8b3035 (git) Affected: 672365477ae8afca5a1cca98c1deb733235e4525 , < 3f735419c4b43cde42e6d408db39137b82474e31 (git) Affected: 672365477ae8afca5a1cca98c1deb733235e4525 , < 388eff894d6bc5f921e9bfff0e4b0ab2684a96e9 (git) |
guessed | |
| Linux | Linux |
Affected:
5.16
Unaffected: 0 , < 5.16 (semver) Unaffected: 6.1.159 , ≤ 6.1.* (semver) Unaffected: 6.6.117 , ≤ 6.6.* (semver) Unaffected: 6.12.58 , ≤ 6.12.* (semver) Unaffected: 6.17.8 , ≤ 6.17.* (semver) Unaffected: 6.18 , ≤ * (original_commit_for_fix) |
guessed |
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"lang": "en",
"value": "In the Linux kernel, the following vulnerability has been resolved:\n\nx86/fpu: Ensure XFD state on signal delivery\n\nSean reported [1] the following splat when running KVM tests:\n\n WARNING: CPU: 232 PID: 15391 at xfd_validate_state+0x65/0x70\n Call Trace:\n \u003cTASK\u003e\n fpu__clear_user_states+0x9c/0x100\n arch_do_signal_or_restart+0x142/0x210\n exit_to_user_mode_loop+0x55/0x100\n do_syscall_64+0x205/0x2c0\n entry_SYSCALL_64_after_hwframe+0x4b/0x53\n\nChao further identified [2] a reproducible scenario involving signal\ndelivery: a non-AMX task is preempted by an AMX-enabled task which\nmodifies the XFD MSR.\n\nWhen the non-AMX task resumes and reloads XSTATE with init values,\na warning is triggered due to a mismatch between fpstate::xfd and the\nCPU\u0027s current XFD state. fpu__clear_user_states() does not currently\nre-synchronize the XFD state after such preemption.\n\nInvoke xfd_update_state() which detects and corrects the mismatch if\nthere is a dynamic feature.\n\nThis also benefits the sigreturn path, as fpu__restore_sig() may call\nfpu__clear_user_states() when the sigframe is inaccessible.\n\n[ dhansen: minor changelog munging ]"
}
],
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"baseScore": 7.8,
"baseSeverity": "HIGH",
"vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
"version": "3.1"
},
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"lang": "en",
"value": "AV:L - The vulnerable code is reached only through local task-context paths \u2014 signal delivery from `arch_do_signal_or_restart()` and the `rt_sigreturn` syscall \u2014 requiring the attacker to execute code on the machine. No network or adjacent-network reachability exists.\nAC:L - The attacker controls both sides of the race: it runs its own AMX-enabled and non-AMX threads, pins them to a chosen CPU, floods signals, and can force a scheduling point in the exact window between `copy_fpstate_to_sigframe()` and `fpu__clear_user_states()` by faulting on userfaultfd-backed sigframe pages. AMX/XFD-capable Xeons (Sapphire Rapids and later) are mainstream cloud/datacenter hardware, so the required configuration is a normal deployment rather than a rare precondition.\nPR:L - Any unprivileged local user can deliver signals to its own threads, call `arch_prctl(ARCH_REQ_XCOMP_PERM, XFEATURE_XTILEDATA)`, set CPU affinity, and invoke `rt_sigreturn` with an inaccessible sigframe \u2014 there is no capability, namespace, or LSM check anywhere on the path.\nUI:N - The attacker triggers the entire sequence from its own processes via signals and scheduling; no action by any other user is required.\nS:U - The XFD desync and its consequences stay within the kernel\u0027s own security authority on the host \u2014 there is no guest-to-host escape, IOMMU bypass, or other crossing of a security-authority boundary.\nC:H - The stale XFD causes the XRSTOR that is specifically responsible for scrubbing dynamic-feature state left by the previous task to skip XTILEDATA, and `fpregs_mark_activate()` suppresses the later corrective restore, so up to 8 KiB of another process\u0027s AMX tile register content survives into the attacker\u0027s context and can be dumped with a userspace `XSAVE` after re-enabling XFD via #NM; the debug WARN additionally discloses kernel addresses.\nI:H - The same primitive works in reverse \u2014 attacker-chosen tile register content is left un-scrubbed and becomes the operating state of a victim AMX process, silently corrupting its computation \u2014 and the desync also lets a task use AMX with no `ARCH_REQ_XCOMP_PERM` grant while its fpstate has no XTILEDATA storage, bypassing the dynamic-xstate permission model and silently discarding FPU state across context switches.\nA:H - The mismatch trips `WARN_ON_ONCE()` in `xfd_validate_state()` from both `os_xrstor()` and the subsequent `os_xsave()` (the reported splat), which is a fatal panic on systems booted with `panic_on_warn=1`, and leaves the FPU state machine persistently inconsistent with the hardware."
}
]
}
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},
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"url": "https://git.kernel.org/stable/c/388eff894d6bc5f921e9bfff0e4b0ab2684a96e9"
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"title": "x86/fpu: Ensure XFD state on signal delivery",
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"cveId": "CVE-2025-68171",
"datePublished": "2025-12-16T13:42:51.121Z",
"dateReserved": "2025-12-16T13:41:40.251Z",
"dateUpdated": "2026-08-05T12:09:59.980Z",
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"date": "2026-10-08",
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"descriptions": [
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"value": "In the Linux kernel, the following vulnerability has been resolved:\n\nx86/fpu: Ensure XFD state on signal delivery\n\nSean reported [1] the following splat when running KVM tests:\n\n WARNING: CPU: 232 PID: 15391 at xfd_validate_state+0x65/0x70\n Call Trace:\n \u003cTASK\u003e\n fpu__clear_user_states+0x9c/0x100\n arch_do_signal_or_restart+0x142/0x210\n exit_to_user_mode_loop+0x55/0x100\n do_syscall_64+0x205/0x2c0\n entry_SYSCALL_64_after_hwframe+0x4b/0x53\n\nChao further identified [2] a reproducible scenario involving signal\ndelivery: a non-AMX task is preempted by an AMX-enabled task which\nmodifies the XFD MSR.\n\nWhen the non-AMX task resumes and reloads XSTATE with init values,\na warning is triggered due to a mismatch between fpstate::xfd and the\nCPU\u0027s current XFD state. fpu__clear_user_states() does not currently\nre-synchronize the XFD state after such preemption.\n\nInvoke xfd_update_state() which detects and corrects the mismatch if\nthere is a dynamic feature.\n\nThis also benefits the sigreturn path, as fpu__restore_sig() may call\nfpu__clear_user_states() when the sigframe is inaccessible.\n\n[ dhansen: minor changelog munging ]"
}
],
"id": "CVE-2025-68171",
"lastModified": "2026-07-30T06:24:31.940",
"metrics": {
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{
"cvssData": {
"attackComplexity": "LOW",
"attackVector": "LOCAL",
"availabilityImpact": "HIGH",
"baseScore": 7.8,
"baseSeverity": "HIGH",
"confidentialityImpact": "HIGH",
"integrityImpact": "HIGH",
"privilegesRequired": "LOW",
"scope": "UNCHANGED",
"userInteraction": "NONE",
"vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
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"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
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"published": "2025-12-16T14:15:48.980",
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"sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
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}
},
"redhat_vex": {
"aggregate_severity": "Low",
"current_release_date": "2026-07-30T10:07:41+00:00",
"cve": "CVE-2025-68171",
"id": "CVE-2025-68171",
"initial_release_date": "2025-12-16T00:00:00+00:00",
"product_status:known_affected": "232",
"product_status:known_not_affected": "42",
"source": "Red Hat CSAF VEX",
"status": "final",
"title": "kernel: x86/fpu: Ensure XFD state on signal delivery",
"url": "https://security.access.redhat.com/data/csaf/v2/vex/2025/cve-2025-68171.json",
"version": "3"
},
"suse_vex": {
"aggregate_severity": "moderate",
"current_release_date": "2026-10-09T00:47:31Z",
"cve": "CVE-2025-68171",
"id": "CVE-2025-68171",
"initial_release_date": "2025-12-17T00:26:21Z",
"product_status:known_affected": "612",
"product_status:known_not_affected": "260",
"product_status:recommended": "289",
"source": "SUSE CSAF VEX",
"status": "interim",
"title": "SUSE CVE CVE-2025-68171",
"url": "https://ftp.suse.com/pub/projects/security/csaf-vex/cve-2025-68171.json",
"version": "38"
}
}
}
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Experimental. This forecast is provided for visualization only and may change without notice. Do not use it for operational decisions.
Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.
Sightings
| Author | Source | Type | Date | Other |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or observed by the user.
- Confirmed: The vulnerability has been validated from an analyst's perspective.
- Published Proof of Concept: A public proof of concept is available for this vulnerability.
- Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
- Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
- Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
- Not confirmed: The user expressed doubt about the validity of the vulnerability.
- Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.
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The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the
vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base
model, served locally by ML-Gateway.
They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.
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Related by attack behaviour
Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.
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