[CVE-2026-98532][IMPORTANT] ipv6: do not let ipv6_find_hdr() return an offset past the packet end

[CVE-2026-98532][IMPORTANT] ipv6: do not let ipv6_find_hdr() return an offset past the packet end

[AL-KERNEL]

CVE: CVE-2026-98532
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: NO
Patch: ipv6: do not let ipv6_find_hdr() return an offset past the packet end
Commit: ca96b38730e31357ef4a9d76af1336958ac670d7
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ca96b38730e31357ef4a9d76af1336958ac670d7
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98532
Analysis date: Sat, 24 Oct 2026 03:15:56 -0400
ActionableScore: 5
ActionableScore lower bound: unknown
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES

Summary:
Malformed IPv6 extension lengths can drive Open vSwitch checksum processing to perform a two-byte heap OOB write and plausibly crash the kernel.

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

The original Linux kernel CVE announcement for CVE-2026-98532 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98532

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-2026-98532	IMPORTANT	https://www.kernelcve.org/list/?q=CVE-2026-98532 CHECK WITH IMPACT FROM ORIG NN MODERATE | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=1 LEGACY=IMPORTANT RESULT=DIFF INDEPENDENT_LEGACY=IMPORTANT INDEPENDENT_RESULT=DIFF TEMP_KPANIC_MERGE=IMPORTANT_WINS_DISAGREEMENT 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:H/A:H';*CWE-787;CWE-125;*CWE-20;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7.8';DESCR 'ipv6_find_hdr trusted extension header lengths and could return an offset beyond the skb end. Open vSwitch then used that offset as the transport header and checksum adjustment performed a two byte out of bounds read and write in kernel heap memory. The demonstrated trigger uses ovs_packet_cmd_execute through the local generic netlink control plane. For the CVSS the PR:L rating reflects the need for local Open vSwitch datapath access or delegated CAP_NET_ADMIN while avoiding PR:H for container root or a restricted network service account. Availability impact is high because the access can crash the kernel. Limited confidentiality and integrity impact is defensible for the base score because a concrete kernel OOB read and write exists. The paranoid score uses high confidentiality and integrity because corruption of an adjacent slab object could potentially support privilege escalation, although no reliable arbitrary write or escalation chain is established. Direct remote reachability from ordinary IPv6 traffic is not demonstrated by this call path. Automated impact decision path. The original SimpleNet classifier selected MODERATE_KPANIC. The primary LLM estimated paranoid CVSS 7.8 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 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_WINS and KPANIC_UNSUPPORTED_REMOVED. The independent weaker Aegis shadow evaluated CVSS 4.6 and ActionableScore 1 with primitive class CLASS_B 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	REMOTE READ OOB DANGER UAF NETWORK SKB HARDWARE IPV6 PACKET INCREASED_TO_HIGH_BASED_ON_GUESSCVSS TEMP_KPANIC_MERGE_IMPORTANT_WINS KPANIC_UNSUPPORTED_REMOVED	-	-	checked

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

ActionableScore=5
PrimitiveClass=CLASS_A
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO
RequiresHostUID0=NO
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO

1. ActionableScore

* Raw base score: 3.
* Conservative score: 5. Manual-review safety floor applied because this is a confirmed attacker-influenced heap OOB write.
* Raw paranoid score: 3.
* Paranoid score: 5. No additional speculative exploit point awarded.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::

2. Signal breakdown

* +2 — Strong corruption primitive: malformed IPv6 extension lengths produce an attacker-influenced transport offset beyond `skb->len`; Open vSwitch checksum adjustment performs a two-byte heap OOB write.
* +1 — Reliable kernel crash/strong DoS: KASAN demonstrates access into a freed slab region, making a kernel fault plausible.
* +1 — Packet-processing path: the bad offset is consumed by Open vSwitch action execution and checksum mutation.
* -1 — Reduced/delegated privilege: supplied evidence places the demonstrated path behind local Open vSwitch datapath access or delegated `CAP_NET_ADMIN`, rather than ordinary unprivileged packet reception.
* Safety floor 3 -> 5 — confirmed, attacker-influenced kernel heap OOB write requires actionable review.

Not awarded: arbitrary payload or arbitrary target, controlled reclaim, adjacent victim control, disclosure, LPE, remote reachability, or extra availability. The KASAN “use-after-free” report describes the allocation state at the OOB address; it does not establish a stale-object UAF in the vulnerable logic. B5-R does not apply because no retry-accumulated index exists.

3. Reachability analysis

The grounded trigger is local `ovs_packet_cmd_execute()` over generic netlink from UID 1000. Thus host UID 0 is not required, and supplied evidence supports a delegated/below-host-admin actor. The exact capability namespace and whether all OVS setup and execution stages are namespace-scoped are not established, so `NamespaceScopedPrivilege=UNKNOWN`. Ordinary remote IPv6 traffic is not shown to reach this path.

4. Primitive and severity reading

The primitive is a bounded-width but attacker-positioned two-byte heap OOB read/write caused by accepting an extension header whose declared length exceeds the packet. The offset is installed as active transport-header state and consumed by privileged kernel checksum code. This is CLASS_A due to the confirmed heap OOB write, but arbitrary write, controlled adjacent-object corruption, confidentiality impact, and privilege escalation remain unproven. Important review is required; automatic downgrade would discard a concrete corruption primitive.

5. One-sentence report phrase

Malformed IPv6 extension lengths can drive Open vSwitch checksum processing to perform a two-byte heap OOB write and plausibly crash the kernel.

6. Manual review advice

MANUAL CHECK REQUIRED

Confirm capability and namespace scope and assess adjacent-slab corruption leverage beyond the demonstrated crash.

7. Call-site confidence

Call-site confidence: high

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

Patch: ipv6: do not let ipv6_find_hdr() return an offset past the packet end
Commit: ca96b38730e31357ef4a9d76af1336958ac670d7
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ca96b38730e31357ef4a9d76af1336958ac670d7

Commit description:

ipv6_find_hdr() walks the extension header chain, skipping each header by
the length that header itself declares.  ipv6_optlen() returns up to 2048,
and the skip is never checked against skb->len, so the offset stored in
*offset can point past the end of the packet.

openvswitch installs that offset as the transport header, and
update_ipv6_checksum() then reads and writes the transport checksum field
out of bounds:

  BUG: KASAN: slab-use-after-free in inet_proto_csum_replace16+0x445/0x470
  Read of size 2 at addr ffff88810b754b06 by task ovs_ipv6_oob/629
  CPU: 4 UID: 1000 PID: 629 Comm: ovs_ipv6_oob Tainted: G N 7.3.0-rc3+ #348
  Call Trace:
   inet_proto_csum_replace16+0x445/0x470
   set_ipv6_addr+0x3dd/0x460
   do_execute_actions+0x6a3d/0x7c40
   ovs_execute_actions+0xfd/0x480
   ovs_packet_cmd_execute+0xc38/0xf20
   genl_rcv_msg+0x59e/0x870
   netlink_rcv_skb+0x18b/0x450
   genl_rcv+0x2d/0x40
   netlink_unicast+0x6bc/0xa20

  The buggy address belongs to the object at ffff88810b754980
   which belongs to the cache skbuff_small_head of size 704
  The buggy address is located 390 bytes inside of
   freed 704-byte region [ffff88810b754980, ffff88810b754c40)

Other callers use that offset too, so bound it here rather than in one
caller.

Reject a header whose declared length does not fit in the packet.
ipv6_find_hdr() already fails with -EBADMSG on a malformed chain, so this
adds no new failure mode.

Fixes: f8f6267 ("ipv6: Move ipv6_find_hdr() out of Netfilter code.")
Suggested-by: Ilya Maximets <i.maximets@ovn.org>
Suggested-by: Eric Dumazet <edumazet@google.com>
Cc: stable@vger.kernel.org
Signed-off-by: Norbert Szetei <norbert@doyensec.com>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Reviewed-by: Ilya Maximets <i.maximets@ovn.org>
Link: https://patch.msgid.link/8F80BA1A-DDFD-432D-9075-242A3435FEB5@doyensec.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  net/ipv6/exthdrs_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=ca96b38730e31357ef4a9d76af1336958ac670d7

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

The original Linux kernel CVE announcement for CVE-2026-98532 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98532

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:L/A:H
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 7.8

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