CVE Intelligence
Unknown

CVE-2025-40122 — perf/x86/intel: Fix IA32_PMC_x_CFG_B MSRs access error

In the Linux kernel, the following vulnerability has been resolved: perf/x86/intel: Fix IA32_PMC_x_CFG_B MSRs access error When running perf_fuzzer on PTL, sometimes the below "unchecked MSR access error" is seen when accessing IA32_PMC_x_CFG_B MSRs. [ 55.611268] unchecked MSR access error: WRMSR to 0x1986 (tried to write 0x0000000200000001) at rIP: 0xffffffffac564b28 (native_write_msr+0x8/0x30) [ 55.611280] Call Trace: [ 55.611282] <TASK> [ 55.611284] ? intel_pmu_config_acr+0x87/0x160 [ 55.611289] intel_pmu_enable_acr+0x6d/0x80 [ 55.611291] intel_pmu_enable_event+0xce/0x460 [ 55.611293] x86_pmu_start+0x78/0xb0 [ 55.611297] x86_pmu_enable+0x218/0x3a0 [ 55.611300] ? x86_pmu_enable+0x121/0x3a0 [ 55.611302] perf_pmu_enable+0x40/0x50 [ 55.611307] ctx_resched+0x19d/0x220 [ 55.611309] __perf_install_in_context+0x284/0x2f0 [ 55.611311] ? __pfx_remote_function+0x10/0x10 [ 55.611314] remote_function+0x52/0x70 [ 55.611317] ? __pfx_remote_function+0x10/0x10 [ 55.611319] generic_exec_single+0x84/0x150 [ 55.611323] smp_call_function_single+0xc5/0x1a0 [ 55.611326] ? __pfx_remote_function+0x10/0x10 [ 55.611329] perf_install_in_context+0xd1/0x1e0 [ 55.611331] ? __pfx___perf_install_in_context+0x10/0x10 [ 55.611333] __do_sys_perf_event_open+0xa76/0x1040 [ 55.611336] __x64_sys_perf_event_open+0x26/0x30 [ 55.611337] x64_sys_call+0x1d8e/0x20c0 [ 55.611339] do_syscall_64+0x4f/0x120 [ 55.611343] entry_SYSCALL_64_after_hwframe+0x76/0x7e On PTL, GP counter 0 and 1 doesn't support auto counter reload feature, thus it would trigger a #GP when trying to write 1 on bit 0 of CFG_B MSR which requires to enable auto counter reload on GP counter 0. The root cause of causing this issue is the check for auto counter reload (ACR) counter mask from user space is incorrect in intel_pmu_acr_late_setup() helper. It leads to an invalid ACR counter mask from user space could be set into hw.config1 and then written into CFG_B MSRs and trigger the MSR access warning. e.g., User may create a perf event with ACR counter mask (config2=0xcb), and there is only 1 event created, so "cpuc->n_events" is 1. The correct check condition should be "i + idx >= cpuc->n_events" instead of "i + idx > cpuc->n_events" (it looks a typo). Otherwise, the counter mask would traverse twice and an invalid "cpuc->assign[1]" bit (bit 0) is set into hw.config1 and cause MSR accessing error. Besides, also check if the ACR counter mask corresponding events are ACR events. If not, filter out these counter mask. If a event is not a ACR event, it could be scheduled to an HW counter which doesn't support ACR. It's invalid to add their counter index in ACR counter mask. Furthermore, remove the WARN_ON_ONCE() since it's easily triggered as user could set any invalid ACR counter mask and the warning message could mislead users.

Published Nov 12, 2025 · Updated Oct 13, 2026 · Sources: NIST National Vulnerability Database, CVE Program (cve.org) e CISA ADP · CNA: Linux

Who exploits it and how urgent it is

A 0–100 score combining confirmed exploitation, ransomware and APT use, public exploits, EPSS and severity.

No exploitation signal in the sources consulted so far.
How the score was calculated
  • EPSS 0.2% (30-day exploitation probability)+1

The score orders the patch queue; it does not replace your asset context (internet exposure, criticality, compensating controls).

Triage

Is it exploited, how likely is exploitation, what does it touch, and how severe do the sources call it.

Exploitation
Not confirmed
Not in CISA KEV — an absence of record, not proof it is unexploited.
EPSS FIRST
0.2%
ahead of 9% of scored CVEs · Oct 15, 2026
Affects
Linux
Linux
CVSS base
—
Score not published yet.

Remediation

Fixes and mitigations documented by the sources — linked to the original advisory.

No fix documented by the sources we poll. That does not mean none exists: check the vendor advisory.

First 24 hours

Ordered from the record’s own fields — exposure first, because you cannot patch what you have not found. A rule-generated starting point.

  1. Identify exposed assets running the affected vendor/product/version combinations (Linux Linux).
  2. No fix documented in the sources: reduce exposure and monitor the vendor advisory.
  3. Search available logs for exploit probes, errors and authentication anomalies.

Affected scope

Vendor, product and versions as the sources word them.

VendorProductVersionsStatusSource
Linux Linux ≥ ec980e4facef8110f6fce27e5b6344660117f01f and < c6cca4213b618c92e4972919ee568f0fb87313b1≥ ec980e4facef8110f6fce27e5b6344660117f01f and < 43796f30507802d93ead2dc44fc9637f34671a89version 6.16 Vulnerable CVE Program (cve.org) e CISA ADP

EPSS over time FIRST

Oct 13, 2026 → Oct 15, 2026 · 3 reading(s) · max 0.20%

Detection

Read off the CVSS vector and the weakness class. Starting points, not tested rules.

  • Not enough vector or weakness data: use the affected application’s logs as a starting point.
application logs

Timeline

What happened to this CVE, newest first.

  • 2026
  • Record published
    Oct 13, 2026
  • Affected products added · linux/linux
    Oct 13, 2026 · CVE Program (cve.org) e CISA ADP
  • Source status changed · → Deferred
    Oct 13, 2026 · NIST National Vulnerability Database
  • Record created in this database
    Oct 13, 2026 · NIST National Vulnerability Database
  • 2025
  • CVE published
    Nov 12, 2025 · Linux

Source activity

Repeated readings are counted rather than listed.

  • 1× Official description updated · Oct 13, 2026 – Oct 13, 2026

References

2 on the record

Elsewhere on this site

Linux
every CVE for this vendor

Related CVEs (same products)

  • CVE-2026-99999 ipv4: validate checksum_start before completing checksum 15h
  • CVE-2026-98432 ipv4: free inet_opt and ireq_opt after an RCU grace period 15h
  • CVE-2026-98424 wifi: cfg80211: undo netns switch if renaming the wiphy fails 1d
  • CVE-2026-98425 wifi: mac80211: don't warn when an IBSS has no channel to scan 1d
  • CVE-2026-98426 wifi: mwifiex: fix IRQ leak using wrong index in MSI-X error path 1d
  • CVE-2026-98427 net/sched: codel: bound the dropping loop per dequeue call 1d

Not in any source we poll

Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.

  • No CVSS score published by NVD, the CNA, CISA or GitHub so far.
  • No fixed version, patch or mitigation documented.
  • No CISA SSVC assessment.
  • No CWE classification.
  • No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
  • No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
  • No exploit packet captures, log samples, or incident case IDs supplied.

Answered from this record

Text assembled only from the fields above — no additional claims.

What should defenders know first?

CVE-2025-40122 is "perf/x86/intel: Fix IA32_PMC_x_CFG_B MSRs access error", rated Unknown. It affects Linux (Linux); versions are in the scope table. It is not in CISA KEV, which does not rule out exploitation. EPSS 0.20% estimates the probability of exploitation in 30 days; neither replaces your asset context. First verify whether exposed or business-critical assets run the affected versions, apply vendor fixes or mitigations, and preserve logs for review.

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