[CVE-2026-97602][MODERATE 7.0] inet: frags: invalidate queues before flushing them

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

CVE: CVE-2026-97602
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: inet: frags: invalidate queues before flushing them
Commit: b9d77f1652e79e58eac48430d0431c329137efcc
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b9d77f1652e79e58eac48430d0431c329137efcc
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97602
Analysis date: Sat, 26 Sep 2026 00:13:22 -0400
ActionableScore: 7
ActionableScore lower bound: unknown
Actionable bucket: Strong Important candidate
Manual review required: YES

Summary:
A local unprivileged user can race IPv6 fragment queue teardown to reuse stale reassembly metadata, causing a confirmed heap out-of-bounds write that can crash the kernel and may enable privilege escalation when unprivileged network namespaces are available.

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

The original Linux kernel CVE announcement for CVE-2026-97602 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97602

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-2026-97602	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-97602 CHECK WITH IMPACT FROM ORIG NN IMPORTANT	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H';CWE-362;*CWE-787;CWE-125;*CWE-664;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'A race during fqdir teardown can leave an incomplete fragment queue reusable with stale IPv6 reassembly metadata after its skbs have been flushed. A new fragment can then be processed with an old nhoffset, causing a slab out of bounds write and a subsequent out of bounds read next to an skbuff_small_head object. The confirmed heap corruption can cause a kernel crash and may be leveraged for local privilege escalation when unprivileged user and network namespaces are available. For the CVSS the PR:L reflects that a local unprivileged user or process is required to create or control the relevant namespace and fragment traffic, even if namespace capabilities provide access to packet sockets. AC:H is used because reliable triggering depends on winning a race during fqdir teardown. The issue is not considered directly network reachable because reliable exploitation requires local namespace lifecycle control rather than only sending packets from a remote host. Impact is at least a local denial of service via kernel crash and in the worst case may allow high confidentiality and integrity impact through the confirmed heap out of bounds write.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate (with actual score 7)  SKIP CVE-2026-97602 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: url YES  NO NO unknown 	MAYBE	REMOTE READ KASAN OOB NETWORK SKB LINUS IPV6 KPANIC PACKET  DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFDH	-	-	checked

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

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

## 1. ActionableScore

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

## 2. Signal breakdown

Positive signals:

* +2 Strong corruption primitive. Stale `nhoffset` is applied to a new skb and causes a confirmed one-byte slab out-of-bounds write next to a `skbuff_small_head` object.
* +2 Strong LPE plausibility. The supplied security analysis explicitly states that the resulting heap corruption can be leveraged for local privilege escalation when unprivileged network namespaces are available.
* +1 Local unprivileged trigger. Under the stated configuration, an ordinary user can create the required namespaces, obtain namespace-scoped networking capabilities, generate fragment traffic, and initiate namespace teardown.
* +1 Reliable kernel crash or strong DoS. KASAN confirms both an out-of-bounds write and a subsequent out-of-bounds read in active IPv6 packet processing, making kernel failure a realistic consequence.
* +1 Common networking packet-processing path. The corruption reaches IPv6 fragment reassembly and subsequent protocol delivery rather than remaining confined to passive cleanup bookkeeping.

No negative signals were applied:

* No race penalty. The bug is a race, but the supplied evidence does not establish a materially uncontrollable one-shot window. Namespace and fragment operations can be repeated.
* No privilege penalty. Below-host-admin reachability is explicitly established when unprivileged network namespaces are enabled.
* No niche-subsystem penalty. IPv6 fragment reassembly is an ordinary networking function, although the vulnerable sequence additionally requires fqdir teardown.
* No constrained-corruption penalty. A real heap write occurs during active skb processing and the supplied analysis identifies LPE leverage.
* No extra Availability point. The same crash was counted only once.
* Confidentiality and Integrity were not separately scored because doing so would double-count the supplied LPE consequence already represented by the +2 strong-leverage signal.
* Controlled arbitrary target selection, arbitrary kernel write, controlled reclaim, and callback hijacking are not demonstrated.
* This is not scored as UAF. The established primitive is reuse of stale reassembly metadata across queue invalidation and flushing, followed by an out-of-bounds access.

## 3. Reachability analysis

The evaluated attacker is an ordinary local user on a system where unprivileged user and network namespace creation is available. The attacker can create the namespace, obtain the networking capabilities scoped to it, generate IPv6 fragment traffic through packet sockets, and drive namespace teardown. This establishes `HostAdminRequired=NO` and `NamespaceScopedPrivilege=YES` for the described complete trigger.

No special hardware is required. The material configuration prerequisite is availability of unprivileged user and network namespaces. Systems that disable this functionality substantially reduce the described low-privilege attack surface.

Direct remote reachability is not established. Remote packets alone do not provide the namespace lifecycle control needed for the demonstrated fqdir teardown race.

The race appears repeatable through namespace creation, fragment transmission, and teardown loops. The evidence does not justify treating it as an externally uncontrollable or one-shot timing condition.

## 4. Primitive and severity interpretation

The exact primitive is an attacker-reachable heap out-of-bounds write followed by an out-of-bounds read. Queue skbs are flushed without first invalidating the incomplete queue. A fragment that already found the queue can later reuse its stale reassembly metadata, causing IPv6 reassembly to apply an old offset to a new skb.

This is active structured-state reuse, not fixed stale storage and not merely a cleanup-time invalid-pointer fault. The stale metadata affects offsets used during subsequent live packet processing. There is no established use-after-free, repeated release, or second refcount mutation.

The primitive is CLASS_A because a concrete attacker-influenced kernel heap overwrite is confirmed and the supplied security analysis explicitly connects it to local privilege escalation. The demonstrated immediate effects are heap corruption, out-of-bounds access, and likely kernel crash. The supported higher consequence is local privilege escalation under the stated namespace configuration. Arbitrary write and a detailed exploit chain remain unshown.

`ImportantCandidate=YES` follows from the concrete heap overwrite and stated LPE leverage. `AutoDowngradeAllowed=NO` because automatically reducing this to an ordinary DoS would discard a confirmed corruption primitive with explicit privilege-escalation relevance.

Likely operational severity is Important on systems permitting unprivileged network namespace creation, with reduced practical exposure where that functionality is disabled.

## 5. One-sentence report phrase

A local unprivileged user can race IPv6 fragment queue teardown to reuse stale reassembly metadata, causing a confirmed heap out-of-bounds write that can crash the kernel and may enable privilege escalation when unprivileged network namespaces are available.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

The patch establishes attacker-reachable kernel heap corruption and the supplied analysis identifies local privilege-escalation leverage, while the exact overwrite control and exploitation chain still require validation.

## 7. Call-site confidence

Call-site confidence: high

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

Patch: inet: frags: invalidate queues before flushing them
Commit: b9d77f1652e79e58eac48430d0431c329137efcc
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b9d77f1652e79e58eac48430d0431c329137efcc

Commit description:

fqdir_pre_exit() flushes the skbs from incomplete queues without
changing their completion state. A fragment which found a queue before
high_thresh was cleared can then acquire the queue lock and reuse stale
reassembly metadata. A queue concurrently killed after fqdir->dead is
set can instead become INET_FRAG_COMPLETE|INET_FRAG_HASH_DEAD while
still holding its old skbs; skipping it because it is complete leaves
those references behind until asynchronous fqdir teardown.

For IPv6, stale metadata can make ip6_frag_reasm() use the old
nhoffset with a new skb and access memory out of bounds. The resulting
heap corruption can be leveraged for local privilege escalation when
unprivileged network namespaces are available. Unflushed fragments can
also keep conntrack references alive after the conntrack per-net
cleanup point.

Kill each incomplete queue, then flush every queue still owned by the
dying rhashtable. HASH_DEAD identifies that ownership, while complete
queues without it are already owned by another destroy path and must be
left alone. Releasing a timer reference removed by inet_frag_kill() is
deferred to inet_frag_putn(), after the queue lock is dropped.

KASAN report:

  BUG: KASAN: slab-out-of-bounds in ipv6_frag_rcv (net/ipv6/reassembly.c:289 (discriminator 2) net/ipv6/reassembly.c:229 (discriminator 2) net/ipv6/reassembly.c:391 (discriminator 2))
  Write of size 1 at addr ff110001039c6e00 by task poc/771
  Call Trace:
  ? ipv6_frag_rcv (net/ipv6/reassembly.c:289 (discriminator 2) net/ipv6/reassembly.c:229 (discriminator 2) net/ipv6/reassembly.c:391 (discriminator 2))
  ipv6_frag_rcv (net/ipv6/reassembly.c:289 (discriminator 2) net/ipv6/reassembly.c:229 (discriminator 2) net/ipv6/reassembly.c:391 (discriminator 2))
  ip6_protocol_deliver_rcu (net/ipv6/ip6_input.c:479 (discriminator 5))
  ip6_input_finish (net/ipv6/ip6_input.c:534)
  ipv6_rcv (include/net/dst.h:480 (discriminator 3) net/ipv6/ip6_input.c:119 (discriminator 3) net/ipv6/ip6_input.c:109 (discriminator 3) include/linux/netfilter.h:325 (discriminator 3) include/linux/netfilter.h:319 (discriminator 3) net/ipv6/ip6_input.c:351 (discriminator 3))
  packet_sendmsg (net/packet/af_packet.c:3110 net/packet/af_packet.c:3142)
  __x64_sys_sendmmsg (net/socket.c:2883 net/socket.c:2880 net/socket.c:2880)
  The buggy address belongs to the object at ff110001039c6b40
  which belongs to the cache skbuff_small_head of size 704
  The buggy address is located 0 bytes to the right of
  allocated 704-byte region [ff110001039c6b40, ff110001039c6e00)

  BUG: KASAN: slab-out-of-bounds in ip6_protocol_deliver_rcu (net/ipv6/ip6_input.c:423 (discriminator 1))
  Read of size 1 at addr ff110001039c6e08 by task poc/771
  Call Trace:
  ? ip6_protocol_deliver_rcu (net/ipv6/ip6_input.c:423 (discriminator 1))
  ip6_protocol_deliver_rcu (net/ipv6/ip6_input.c:423 (discriminator 1))
  ip6_input_finish (net/ipv6/ip6_input.c:534)
  ipv6_rcv (include/net/dst.h:480 (discriminator 3) net/ipv6/ip6_input.c:119 (discriminator 3) net/ipv6/ip6_input.c:109 (discriminator 3) include/linux/netfilter.h:325 (discriminator 3) include/linux/netfilter.h:319 (discriminator 3) net/ipv6/ip6_input.c:351 (discriminator 3))
  packet_sendmsg (net/packet/af_packet.c:3110 net/packet/af_packet.c:3142)
  __x64_sys_sendmmsg (net/socket.c:2883 net/socket.c:2880 net/socket.c:2880)
  packet_sendmsg (net/packet/af_packet.c:2959 net/packet/af_packet.c:3053 net/packet/af_packet.c:3142)
  __x64_sys_sendmmsg (net/socket.c:2883 net/socket.c:2880 net/socket.c:2880)
  The buggy address belongs to the object at ff110001039c6b40
  which belongs to the cache skbuff_small_head of size 704
  The buggy address is located 8 bytes to the right of
  allocated 704-byte region [ff110001039c6b40, ff110001039c6e00)

Fixes: 006a503 ("inet: frags: flush pending skbs in fqdir_pre_exit()")
Cc: stable@vger.kernel.org
Reported-by: Kimi Security Team <bug-report@moonshot.ai>
Tested-by: Weiming Shi <shiweiming@moonshot.ai>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Yilin Zhang <yilinzhang@moonshot.ai>
Link: https://patch.msgid.link/20260904162800.1095662-1-yilinzhang@moonshot.ai
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  net/ipv6/reassembly.c
  net/ipv6/ip6_input.c
  include/net/dst.h
  include/linux/netfilter.h
  net/packet/af_packet.c
  net/socket.c
  net/ipv4/inet_fragment.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=b9d77f1652e79e58eac48430d0431c329137efcc

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

The original Linux kernel CVE announcement for CVE-2026-97602 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97602

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:H/PR:L/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 7

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: 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).