[CVE-2026-80977][MODERATE 7.0] net: skbuff: don't touch shared zerocopy state in skb_tx_error()

[CVE-2026-80977][MODERATE 7.0] net: skbuff: don't touch shared zerocopy state in skb_tx_error()

[AL-KERNEL]

CVE: CVE-2026-80977
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: net: skbuff: don't touch shared zerocopy state in skb_tx_error()
Commit: 15aa81b390d401abf4b8211042470e9e92e3b7fb
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=15aa81b390d401abf4b8211042470e9e92e3b7fb
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80977
Analysis date: Fri, 11 Sep 2026 17:45:32 -0400
ActionableScore: 7
ActionableScore lower bound: 6
Actionable bucket: Strong Important candidate
Manual review required: YES

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-80977 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80977

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 7.0
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-2026-80977	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-80977 CHECK WITH IMPACT FROM ORIG NN LOW	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H';*CWE-416;*CWE-664;CWE-362;Other CVSS 'AV:A/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7.5';DESCR 'skb_tx_error() could modify zerocopy flags stored in skb_shinfo() for a cloned skb even though skb_shinfo() is shared by all clones. In an Open vSwitch recirculation path this can clear shared frag ownership state on one clone while the original skb is still in flight, letting later ESP local delivery decrypt in place over frags that are not privately owned. For the CVSS the PR:N means the attacker may only need network access to the affected datapath after OVS and ESP processing are configured by the victim. The issue is best treated as network adjacent because practical triggering depends on being able to inject traffic into the relevant switching or tunneling path. Impact is at least denial of service and in the worst case may include confidentiality or integrity impact due to stale zerocopy page ownership and possible use-after-free style memory corruption.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate (with actual score 7)	YES	REMOTE UAF SKB HARDWARE KPANIC PACKET  KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFDH	NO	NO	checked

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

ActionableScore=7
ActionableScoreLower=6
PrimitiveClass=CLASS_A
RealUAF=YES
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO

1. ActionableScore

* Raw conservative score: 6
* Conservative score: 6. No floor or cap applied.
* Raw paranoid score: 7
* Paranoid score: 7. No floor or cap applied.
* Final recommended bucket: **Strong Important candidate**::

2. Signal breakdown

Positive signals for conservative score:

* +2. Demonstrated shared-page / page-frag ownership violation. `skb_tx_error()` can clear zerocopy/shared-frag state in shared `skb_shinfo()` through a clone while another skb using the same fragments remains in flight.
* +2. Network-reachable in the affected datapath. The described trigger is packet-driven through Open vSwitch recirculation and later ESP local delivery, assuming the victim has the OVS plus ESP path configured.
* +1. Integrity impact is plausible. The commit explicitly describes ESP decrypting in place over fragments that the skb does not privately own.
* +1. Concrete practical chain is described. The commit gives a specific sequence: non-last OVS recirculation, `skb_clone()`, flow miss on clone, marker removal from original in-flight packet, then ESP in-place decrypt over non-private frags.

Additional paranoid signal:

* +1. Unresolved UAF-style page lifetime leverage. The bug can tell the zerocopy producer that pages are free while another skb still references them, leaving meaningful post-lifetime ownership and reuse risk unresolved.

Important non-awarded signals:

* Controlled reclaim is not demonstrated.
* Arbitrary kernel read/write is not demonstrated.
* Callback or function-pointer control is not demonstrated.
* Extra Availability was not awarded separately because no distinct persistent availability mechanism beyond possible crash/corruption is established.
* Strong LPE was not awarded as a separate +2 because privilege escalation is not demonstrated.
* Race penalty was not applied because the described trigger is a concrete datapath sequence, not merely a narrow timing race.
* Host-admin penalty was not applied because attacker traffic can reach the vulnerable path after the affected datapath is configured by the victim.

3. Reachability analysis

The evaluated attacker is a network-adjacent or network-positioned sender able to inject traffic into the relevant OVS and ESP processing path. The attacker does not need host-admin privileges on the target for the packet-trigger stage, but the vulnerable path depends on prior victim configuration of Open vSwitch recirculation and local ESP delivery. This is not best treated as arbitrary Internet-wide exposure. It is more realistic for data-center, overlay, virtual switching, or tunneling deployments where untrusted or tenant-controlled traffic enters the configured datapath.

No namespace-scoped privilege is required for the attacker model used here. The trigger is not a local netlink or CAP_NET_ADMIN operation by the attacker. Special hardware is not established. The path is configuration-specific but not rare enough to justify a generic niche-subsystem penalty.

4. Primitive and severity interpretation

The exact primitive is corruption of shared skb zerocopy/page-frag ownership state through a cloned skb. The affected storage is active shared packet fragment state, not fixed stale storage. The commit describes a meaningful ownership violation where one clone clears state shared with another skb that is still being forwarded, and later ESP processing writes in place to fragments not privately owned by that skb.

This is stronger than a crash-only invalid dereference. It is a shared-page/page-lifetime ownership violation with UAF-style consequences because pages may be reported free while still in active use. The demonstrated consequence is at least memory ownership corruption and possible DoS. The speculative consequence is broader confidentiality or integrity impact if page reuse or stale fragment ownership can be exploited beyond packet corruption, but controlled reclaim or arbitrary R/W is not shown.

PrimitiveClass is CLASS_A because a concrete shared-page/page-frag ownership violation with in-place write into non-private fragments is established. ImportantCandidate is YES because the primitive is security-relevant and should not be reduced to ordinary Moderate based only on lack of a complete exploit. AutoDowngradeAllowed is NO because automatically closing would discard an unresolved concrete ownership/lifetime corruption primitive.

5. One-sentence report phrase

`skb_tx_error() can modify zerocopy state shared through skb_shinfo() for cloned skbs, allowing an OVS recirculation plus ESP path to clear shared frag ownership while another skb is still in flight and later decrypt in place over non-private fragments.`

6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: concrete shared skb fragment ownership and UAF-style lifetime corruption is established, with packet-driven reachability in configured OVS/ESP deployments and unresolved exploitation leverage beyond a simple crash.

7. Call-site confidence

Call-site confidence: high

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

Patch: net: skbuff: don't touch shared zerocopy state in skb_tx_error()
Commit: 15aa81b390d401abf4b8211042470e9e92e3b7fb
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=15aa81b390d401abf4b8211042470e9e92e3b7fb

Commit description:

skb_tx_error() completes the zerocopy uarg and clears
SKBFL_ALL_ZEROCOPY, and skb_zcopy_downgrade_managed() clears
SKBFL_MANAGED_FRAG_REFS. Both live in skb_shinfo(), which every clone
shares, while the caller only owns the reference it is about to drop.
Through a clone it tells the producer its pages are free and drops
SKBFL_SHARED_FRAG for an skb that is still in flight.

Open vSwitch reaches this with a non-last OVS_ACTION_ATTR_RECIRC:
clone_execute() sends a skb_clone() into ovs_dp_process_packet() while
do_execute_actions() keeps forwarding the original, and skb_clone()
does not privatise the frags here -- skb_orphan_frags() returns early
on SKBFL_DONT_ORPHAN. A flow miss on the clone then strips the marker
from the packet still being forwarded, and a later local ESP delivery
decrypts in place over frags it does not own privately.

Skip it for a cloned skb. Nothing is lost: skb_release_data() clears
the zerocopy state once the last reference to the shared data goes.

Fixes: 2512117 ("skb: api to report errors for zero copy skbs")
Cc: stable@vger.kernel.org
Suggested-by: Ilya Maximets <i.maximets@ovn.org>
Signed-off-by: Norbert Szetei <norbert@doyensec.com>
Reviewed-by: Ilya Maximets <i.maximets@ovn.org>
Tested-by: Jongmin Jang <payload.jang@gmail.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Link: https://patch.msgid.link/CFAB292A-674B-4C14-BB2C-BB8830AD5659@doyensec.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  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=15aa81b390d401abf4b8211042470e9e92e3b7fb

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

The original Linux kernel CVE announcement for CVE-2026-80977 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80977

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:L/I:L/A:H
  The Best / paranoid CVSS vector: AV:A/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 7.5

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: 6
  Paranoid ActionableScore: 7

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: YES
Published priority for this report (same as in Subject): MODERATE 7.0

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).