* [CVE-2026-98655][IMPORTANT] perf: Require kernel access for text poke events [ Upstream
@ 2026-10-19 3:38 21% AL-KERNEL
0 siblings, 0 replies; 1+ results
From: AL-KERNEL @ 2026-10-19 3:38 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-98655
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: NO
Patch: perf: Require kernel access for text poke events [ Upstream
Commit: 8473f44db9f710ea6f8cafb22f2e3ba6cb8ca9a7
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=8473f44db9f710ea6f8cafb22f2e3ba6cb8ca9a7
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98655
Analysis date: Sun, 18 Oct 2026 23:38:29 -0400
ActionableScore: 5
ActionableScore lower bound: unknown
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES
Summary:
A local unprivileged task can bypass the kernel perf access check for text poke events and recover the runtime kernel text base from raw instruction addresses, defeating KASLR without independently obtaining arbitrary memory access or elevated privileges.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98655 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98655
The original announcement does not normally provide a security severity
estimate, CVSS assessment, or enough information to determine whether the
reported kernel bug represents a practically relevant security issue.
This report was generated by AL-KERNEL, an AI-assisted Linux kernel
vulnerability analysis system developed by Alexander Larkin. It combines
an autonomous classifier with LLM-assisted technical analysis and a
separate ActionableScore mechanism.
The purpose of this report is to prioritize Linux kernel CVEs before
manual review, identify cases that require prompt investigation, and
support automatic closure of issues that are unlikely to have meaningful
security impact.
Published priority for this report: IMPORTANT
Manual review required: YES
A detailed explanation of the methodology and priority rules is included
at the end of this message.
======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================
CVE-2026-98655 IMPORTANT https://www.kernelcve.org/list/?q=CVE-2026-98655 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=4 LEGACY=IMPORTANT RESULT=DIFF INDEPENDENT_LEGACY=IMPORTANT INDEPENDENT_RESULT=DIFF TEMP_KPANIC_MERGE=IMPORTANT_HARD_VETO PRE_MERGE_LEGACY=IMPORTANT (final Legacy and Aegis differ; FINAL: IMPORTANT, Aegis: MODERATE_KPANIC) Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N';*CWE-200;CWE-862;CWE-284;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N';BEST CVSS score: '5.5';DESCR 'An authorization gap in perf_event_open allows a local unprivileged task to request text poke sideband records while exclude_kernel is set. PERF_RECORD_TEXT_POKE records contain raw relocated kernel instruction addresses, so observing a known instruction address reveals the runtime kernel text base and defeats KASLR for a known kernel image. For the CVSS the PR:L value is used because an attacker must have local user access and execute perf_event_open and mmap operations, but no kernel administration privilege is required when the relevant unprivileged perf policy permits the event. The issue is not network reachable. The direct impact is disclosure of kernel address information rather than memory corruption or denial of service. It does not independently provide privilege escalation, but the KASLR bypass can make exploitation of a separate kernel memory corruption flaw more reliable. Automated impact decision path. The original SimpleNet classifier selected MODERATE_KPANIC. The primary LLM estimated paranoid CVSS 5.5 and the production ActionableScore returned 5 with recommendation Actionable Moderate / Strong Important candidate requiring manual review. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were CVSS and initial triage stage MODERATE_KPANIC to IMPORTANT because the CVSS score, vector or bug class threshold rule was applied. final reconciliation stage IMPORTANT to IMPORTANT because a specific evidence based protection or manual review veto was applied and KP specialist did not establish a qualifying panic. The legacy KP specialist produced a review artifact and its decision was processed by the applicable KP rules. The legacy FD or DH downgrade specialist produced a review artifact and its decision was processed by the applicable downgrade and preservation rules. Exact triggered rule markers were INCREASED_TO_HIGH_BASED_ON_GUESSCVSS and TEMP_KPANIC_MERGE_IMPORTANT_VETO and B4_CONFIRMED_AUTHORIZATION_PRESERVE and MANUAL_REVIEW_REQUIRED and KPANIC_UNSUPPORTED_REMOVED. The independent weaker Aegis shadow evaluated CVSS 4.2 and ActionableScore 4 with primitive class CLASS_A and manual review REQUIRED. Its independently reconciled impact was MODERATE_KPANIC. Cross model aggregation changed the production result under an enabled evidence gated merge rule. The final reported impact is IMPORTANT.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 5) MAYBE READ KASAN OOB SIMPLEFIX HARDWARE LINUS INCREASED_TO_HIGH_BASED_ON_GUESSCVSS TEMP_KPANIC_MERGE_IMPORTANT_VETO B4_CONFIRMED_AUTHORIZATION_PRESERVE MANUAL_REVIEW_REQUIRED KPANIC_UNSUPPORTED_REMOVED - - checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=5
PrimitiveClass=CLASS_A
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO
RequiresHostUID0=NO
AuthorizationDecisionBypass=YES
ProtectedResourceImpact=CONFIRMED
B4PendingReview=YES
B4PendingConfirmed=YES
1. ActionableScore
* Raw conservative score: 5
* Conservative score: 5
* Raw paranoid score: 5
* Paranoid score: 5
* No floor or cap was applied.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::
2. Signal breakdown
Positive signals:
* +2 Concrete authorization decision bypass. With `exclude_kernel=1`, requesting `text_poke=1` bypasses `perf_allow_kernel()`. The fix restores this mandatory kernel-access decision.
* +1 Local unprivileged trigger. The commit explicitly establishes that an unprivileged task can open and mmap a task-local software event containing text-poke records.
* +1 Confidentiality plausible. `PERF_RECORD_TEXT_POKE` exposes relocated kernel instruction addresses and therefore the runtime kernel text base for a known image.
* +1 Practical exploit chain. The established chain is `perf_event_open()` to mmap sideband records to raw kernel address disclosure to KASLR bypass.
No negative points were applied.
Important non-awarded signals:
* No UAF, OOB access, memory corruption, arbitrary write, kernel crash, or resource exhaustion is established.
* No direct privilege escalation is established. KASLR disclosure is an exploit-chain enabler, not an independent root primitive.
* No remote reachability is established.
* No extra sensitive-resource-theft score was awarded because the disclosed resource is kernel address information, not a privileged FD, credential, file, or arbitrary kernel memory.
* No additional paranoid point was awarded because stronger consequences require a separate vulnerability.
3. Reachability analysis
An ordinary local user can request a task-local software perf event with `exclude_kernel=1` and `text_poke=1`, then mmap its output. Before the fix, `exclude_kernel=1` prevented the path from calling `perf_allow_kernel()`, even though text-poke records still contained kernel addresses.
The complete demonstrated trigger does not require host UID 0, host-administrator powers, or a namespace capability. It depends on a perf policy that permits the task-local event while denying normal kernel perf access. A count-only tracepoint event can cause an inline static-call update and produce an observable text-poke record. No network attacker path, special hardware, race, or prior namespace setup is required.
4. Primitive and severity interpretation
The exact primitive is an authorization bypass producing a constrained but concrete kernel-address disclosure. The intended kernel-access guard changes from DENY to ALLOW because `attr.text_poke` was omitted from the condition invoking `perf_allow_kernel()`.
The concrete path is:
`perf_event_open()` with `exclude_kernel=1` and `text_poke=1`
to omitted `perf_allow_kernel()` check
to successful event creation and mmap
to `PERF_RECORD_TEXT_POKE` disclosure
to recovery of the runtime kernel text base.
This is CLASS_A under the authorization-bypass profile. It is not memory corruption and does not establish arbitrary kernel reads, host compromise, or privilege escalation. The demonstrated consequence is defeat of KASLR. A subsequent privilege-escalation chain remains speculative and would require a separate memory-corruption or control-flow vulnerability.
`B4PendingConfirmed=YES` because the attacker-invocable caller, omitted authorization guard, below-host-admin credentials, disclosed protected resource, and DENY-to-ALLOW behavior are all established. `ImportantCandidate=YES` and `AutoDowngradeAllowed=NO` preserve this concrete security-boundary bypass for mandatory review, although the standalone operational severity remains Actionable Moderate.
5. One-sentence report phrase
A local unprivileged task can bypass the kernel perf access check for text poke events and recover the runtime kernel text base from raw instruction addresses, defeating KASLR without independently obtaining arbitrary memory access or elevated privileges.
6. Manual review recommendation
MANUAL CHECK REQUIRED
The issue is a confirmed below-host-admin authorization bypass exposing protected kernel address information and enabling a concrete KASLR bypass.
7. Call-site confidence
Call-site confidence: high
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: perf: Require kernel access for text poke events [ Upstream
Commit: 8473f44db9f710ea6f8cafb22f2e3ba6cb8ca9a7
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=8473f44db9f710ea6f8cafb22f2e3ba6cb8ca9a7
Changed files:
kernel/events/core.c
Diff excerpt:
Not included in this email. See the upstream URL for the full patch.
Full patch:
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=8473f44db9f710ea6f8cafb22f2e3ba6cb8ca9a7
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98655 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98655
The original CVE announcement normally does not include a security-level
estimate. In particular, it may not contain a CVSS assessment, an impact
level, or enough information to determine whether the reported bug is a
practically relevant security issue. One purpose of this parallel CVE list
is to provide that missing technical and prioritization information.
The original goal of the AL-KERNEL project was to prioritize Linux kernel
CVE analysis automatically before manual review. The system can also help
identify non-security issues that may be suitable for automatic closure.
This report was generated by AL-KERNEL, an AI-assisted Linux kernel
vulnerability analysis system developed by Alexander Larkin.
The first analysis stage combines an autonomous classifier with additional
LLM-based analysis. The autonomous classifier runs locally on a CPU and is
based on a backpropagation neural network. Together, these mechanisms
produce a technical vulnerability description, identify likely weakness
types, estimate CVSS severity, and provide input for ActionableScore.
Two CVSS estimates are retained because incomplete kernel vulnerability
information often permits more than one defensible interpretation:
Conservative CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N
The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N
The Best / paranoid CVSS score: 5.5
The conservative vector represents a lower-impact interpretation.
The Best/paranoid vector intentionally represents a plausible upper-bound
interpretation and should not automatically be treated as demonstrated
real-world impact.
CVSS may also need to be adjusted for a particular Linux deployment,
because actual reachability, privileges, enabled kernel configuration,
hardware, namespaces, exposed device nodes, and other environmental
conditions can differ significantly between systems.
A separate ActionableScore mechanism evaluates practical remediation
urgency. Its analysis may include reachability, attack prerequisites,
subsystem exposure, memory-corruption characteristics, denial-of-service
reliability, and possible confidentiality, integrity, or
privilege-escalation impact.
Conservative ActionableScore: unknown
Paranoid ActionableScore: 5
The final base severity is taken directly from the second tab-separated
field of the AL-KERNEL classification result. ActionableScore does not
replace or independently override that final AL-KERNEL decision, and
if ActionableScore adjusted impact level of ALKERNEL, then you would see
self-readable flags above like INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN7.
For an AL-KERNEL result of MODERATE, this report uses the following
additional presentation split:
ActionableScore below 5 -> MODERATE REGULAR
ActionableScore 5 or more -> MODERATE 7.0
The distinction between MODERATE REGULAR and MODERATE 7.0 makes it
possible to identify Moderate issues that should receive manual analysis
and fixes before lower-priority MODERATE REGULAR issues. In many cases,
MODERATE REGULAR fixes may wait for a later rebase or routine update.
There is one override in which MODERATE REGULAR becomes MODERATE 7.0
even when the ActionableScore is below 5. When the AL-KERNEL result
contains the KPANIC flag, a MODERATE result is always presented as
MODERATE 7.0. The KPANIC flag selected with few regexps without
usage of AI at all, so it helps to detect cases when Kernel Crash happens
and similar (to filter False-Negative results from the LLM usage).
KPANIC indicates that a reliable kernel crash, kernel panic, or similarly
serious kernel availability impact was identified by the classification
workflow.
AL-KERNEL base severity for this report: IMPORTANT
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): IMPORTANT
These results are intended to support engineering triage. They are
machine-generated estimates, and cases marked for manual review should
be validated by a human security engineer before final disposition.
For more info read docs linked from here: https://kernelcve.org/
(and you can submit you own patch there to generate such a report
for non-existant CVE-id yet).
Note that in many cases this AI tool selects higher severity, than
real is (means you can expect Importants instead of Moderate 7.0 or
Moderates 7.0 instead of regular Moderates). If you see such cases,
please use reply email interface to add additional manual analyses
info to this particular CVE.
And please, please, let me know when you see Lows instead of Importants
or Important instead of Low (because particular for such cases I
need to tune this AI tool to make it better for this one and next similar).
My contact email for such notifications is [email protected] (and both
send reply to CVE record itself too and see "reply" button below for howto reply).
^ permalink raw reply [relevance 21%]
Results 1-1 of 1 | reverse | sort options + mbox downloads above
-- links below jump to the message on this page --
2026-10-19 3:38 21% [CVE-2026-98655][IMPORTANT] perf: Require kernel access for text poke events [ Upstream AL-KERNEL
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox