[CVE-2026-98271][MODERATE REGULAR] net: skbuff: do not leave stale header offsets after pskb_carve() [ Upstream

[AL-KERNEL <alkernel@kernelcve.org>]

CVE: CVE-2026-98271
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: net: skbuff: do not leave stale header offsets after pskb_carve() [ Upstream
Commit: 75e4a3e62531738c124c8555a626426fca29d392
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=75e4a3e62531738c124c8555a626426fca29d392
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98271
Analysis date: Sat, 10 Oct 2026 16:47:13 -0400
ActionableScore: 3
ActionableScore lower bound: 2
Actionable bucket: Borderline / manual review recommended
Manual review required: YES

Summary:
No one-sentence report phrase was found.

======================================================================
ABOUT THIS REPORT
======================================================================

The original Linux kernel CVE announcement for CVE-2026-98271 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98271

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: MODERATE REGULAR
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-2026-98271	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-98271 CHECK WITH IMPACT FROM ORIG NN MODERATE | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=1 LEGACY=MODERATE RESULT=DIFF (independent Legacy and Aegis differ; FINAL: MODERATE, Aegis: MODERATE_KPANIC)	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:H';CWE-665;*CWE-457;CWE-617;Other CVSS 'AV:A/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.9';DESCR 'Stale SKB header offsets can remain after pskb_carve_inside_header or pskb_carve_inside_nonlinear removes the original packet headers and reallocates skb head. The offsets remain inside the allocation but point beyond skb_tail_pointer to bytes that are no longer part of the packet and were not initialized for the new SKB state. In the demonstrated RDS TCP path the carved SKB is queued and later freed through skb_queue_purge. An active drop_monitor consumer can then use the bogus MAC header offset and reach a kernel BUG in __skb_pull, causing a kernel crash and denial of service. For the CVSS the PR:N value is used because no account or privileges on the target are required when an attacker can communicate as an RDS TCP peer. AV:A and AC:H reflect that RDS TCP is normally used on restricted cluster networks and reliable triggering depends on a specific nonlinear SKB layout, message release, and an active drop monitoring path. The base impact is denial of service only. The paranoid score adds C:L because another SKB metadata consumer could potentially expose uninitialized bytes, but there is no supported UAF, out of bounds write, arbitrary write, or credible privilege escalation primitive.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 3)	MAYBE	REMOTE DANGER SKB SYZBOT PACKET  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4	-	-	checked

======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================

ActionableScore=3
ActionableScoreLower=2
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES
RequiresHostUID0=UNKNOWN
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO

1. ActionableScore

* Raw conservative score: 2
* Conservative score: 2
* Raw paranoid score: 3
* Paranoid score: 3
* No floor or cap was applied.
* Final recommended bucket: **Borderline / manual review recommended**::

2. Signal breakdown

Conservative signals:

* +1 Memory layout invariant restoration. Carving reallocates the SKB head and removes its headers, but leaves offsets describing bytes beyond the new logical tail.
* +1 Reliable kernel crash. The documented RDS and drop_monitor path reaches a kernel BUG in `__skb_pull()`.
* Total: 2.

Paranoid signal:

* +1 Confidentiality plausible. The commit identifies `skb_dump()`, drop_monitor, and taps as consumers that may read garbage through offsets pointing at uninitialized bytes. This supports review for limited disclosure, although successful delivery of those bytes to an attacker is not demonstrated.
* Total: 3.

Not awarded:

* No UAF, heap OOB write, double release, controlled reclaim, arbitrary write, or lifetime corruption is established.
* No integrity point because the fix addresses stale metadata and invalid reads or pulls, not modification of protected state.
* No direct-remote +2 because the complete path requires more than generic traffic. The evidence does not fully establish that an unauthenticated peer can reliably force the required nonlinear RDS SKB state and active drop-monitoring path.
* No extra availability point because it would double-count the same kernel BUG.
* No common-network-path point because the vulnerable `pskb_extract()` use is specifically identified in RDS TCP rather than a broadly exercised generic receive path.
* B5-R does not apply because there is no retry-accumulated OOB write.
* B3-PENDING does not apply because there is no write into shared or file-backed storage.
* B4-PENDING does not apply because no authorization decision changes from DENY to ALLOW.

3. Reachability analysis

The visible call chain is `rds_tcp_data_recv()` to `pskb_extract()`, followed by queuing on `ti_skb_list`, release through `rds_tcp_inc_free()` and `skb_queue_purge()`, and consumption by drop_monitor.

An RDS TCP peer can influence incoming message data, but the supplied evidence does not fully prove reliable peer control over the required SKB fragmentation and carving state. The demonstrated crash also depends on an active drop-monitoring consumer or a comparable stale-header consumer. Configuration of RDS and drop monitoring may involve privileged local setup, but this does not prove that the triggering peer itself requires host-admin power.

Therefore, host-admin and namespace privilege requirements remain UNKNOWN. No special hardware, race, retry loop, or narrow timing window is required by the documented mechanics.

4. Primitive and severity interpretation

The exact primitive is stale SKB header metadata after logical packet data has been removed. The offsets remain inside the allocated `skb->head`, so this is not an allocation-bound OOB access. They point beyond `skb_tail_pointer()` into bytes outside the valid packet and potentially into uninitialized storage.

This is invalid structured-state consumption, classified as CLASS_C. It is neither an active-object UAF nor fixed post-lifetime storage. There is no repeated release or refcount mutation.

The demonstrated consequence is a kernel BUG and denial of service. A limited uninitialized-data disclosure through another SKB consumer is technically plausible but unconfirmed. No useful write, ownership violation, authorization bypass, or privilege-escalation primitive remains after excluding the crash.

ImportantCandidate is NO because the evidence does not establish an Important-preserving corruption or boundary primitive. AutoDowngradeAllowed is YES because the demonstrated behavior is constrained invalid-state consumption with crash impact, while the possible disclosure remains unconfirmed.

5. One-sentence report phrase

Stale SKB header offsets after packet carving can make RDS cleanup consumers pull or inspect invalid uninitialized data and can trigger a kernel BUG, while no UAF, OOB write, or privilege escalation primitive is established.

6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Confirm whether an RDS TCP peer can reliably create the required nonlinear SKB state and whether `skb_dump()`, drop_monitor, or tap paths can expose uninitialized bytes before faulting.

7. Call-site confidence

Call-site confidence: high

======================================================================
UPSTREAM PATCH SUMMARY
======================================================================

Patch: net: skbuff: do not leave stale header offsets after pskb_carve() [ Upstream
Commit: 75e4a3e62531738c124c8555a626426fca29d392
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=75e4a3e62531738c124c8555a626426fca29d392

Changed files:
  include/linux/skbuff.h
  net/core/skbuff.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=75e4a3e62531738c124c8555a626426fca29d392

======================================================================
DETAILED REPORT METHODOLOGY
======================================================================

The original Linux kernel CVE announcement for CVE-2026-98271 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98271

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:A/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:A/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:H
  The Best / paranoid CVSS score: 5.9

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: 2
  Paranoid ActionableScore: 3

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: MODERATE
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): MODERATE REGULAR

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 alexanjelausa@gmail.com (and both
send reply to CVE record itself too and see "reply" button below for howto reply).