[CVE-2026-63922][IMPORTANT] ipv6: exthdrs: refresh nh after handling HAO option

[CVE-2026-63922][IMPORTANT] ipv6: exthdrs: refresh nh after handling HAO option

[AL-KERNEL]

CVE: CVE-2026-63922
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: ipv6: exthdrs: refresh nh after handling HAO option
Commit: f8aabed3ff3e986920cf02a2a2785e08e586b234
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f8aabed3ff3e986920cf02a2a2785e08e586b234
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63922
Analysis date: Sun, 19 Jul 2026 17:37:49 -0400
ActionableScore: 7
ActionableScore lower bound: 6
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
An IPv6 extension header parsing flaw can leave `ip6_parse_tlv()` using a stale network header pointer after HAO handling reallocates skb head storage, allowing a remote crafted packet to cause at least a kernel crash and requiring manual review for limited stale-pointer memory exposure risk.

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

The original Linux kernel CVE announcement for CVE-2026-63922 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63922

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.

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AL-KERNEL CLASSIFICATION RESULT
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CVE-2026-63922	IMPORTANT	CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H';*CWE-416;CWE-825;*CWE-672;Other CVSS 'AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'An IPv6 extension header parsing bug can leave ip6_parse_tlv using a stale cached network header pointer after ipv6_dest_hao handles a Home Address Option. ipv6_dest_hao may call pskb_expand_head for a cloned skb, which can move the skb head and invalidate the old nh pointer. A remote peer may trigger this through a crafted IPv6 packet containing an HAO option followed by padding or additional TLVs, but practical triggering depends on Mobile IPv6 support, packet filtering, and whether the skb is cloned in the receive path. For the CVSS the PR:N is used because the paranoid network scenario only requires packet reachability to the IPv6 input path and no local account on the victim is required. Impact is at least denial of service via kernel crash. For the paranoid score, limited confidentiality or integrity impact is kept as a manual review possibility because the stale pointer can become a UAF read during protocol parsing, but there is no clear write primitive in the patch context.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7)	YES	REMOTE OOB SIMPLEFIX NETWORK SKB IPV6 KPANIC  KPANIC INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN7	NO	NO	checked

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

ActionableScore=7
ActionableScoreLower=6

## 1. ActionableScore

* Conservative score: **6**
* Paranoid score: **7**
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Triggered signals:

* **Remote reachable / network-triggerable: +2**
  The affected path is IPv6 extension header parsing. A crafted IPv6 packet with HAO followed by padding or additional TLVs can plausibly reach this code.

* **Memory corruption, weak/indirect corruption candidate: +1**
  The cached `nh` pointer can become stale after `pskb_expand_head()` moves the skb head. The visible primitive is stale pointer use during parsing, not an OOB write or arbitrary write.

* **Real lifetime corruption: +1**
  The old skb head storage may be invalidated after reallocation, so subsequent use of the cached pointer is a stale lifetime issue.

* **Reliable kernel crash / strong DoS: +1**
  Parsing from an invalid stale skb header pointer can plausibly cause an invalid read and kernel crash.

* **Common networking core path or packet-processing path: +1**
  This is in IPv6 extension header parsing, a packet receive path. HAO/Mobile IPv6 makes triggering less common, but the subsystem is still network packet processing.

Paranoid-only additional signal:

* **Confidentiality or integrity impact plausible: +1 total**
  A stale pointer read in a remote packet parser deserves manual review for limited C/I risk, but the patch does not show a write primitive, controlled reclaim, callback control, or arbitrary memory corruption. I do not award strong LPE plausibility.

Not awarded:

* No **Strong LPE plausibility +2** because no attacker-controlled reclaim, overwrite, callback dispatch, or type confusion is shown.
* No **strong memory corruption +2** because the visible primitive is stale pointer read/use after skb head relocation, not a demonstrated write or object replacement primitive.
* No admin privilege penalty because packets can be supplied remotely if the path is reachable.

## 3. Reachability analysis

A remote sender may trigger the bug by sending IPv6 packets containing the Home Address Option and trailing TLVs or padding. Practical reachability depends on whether Mobile IPv6 HAO support is enabled, whether such packets are filtered, and whether the skb is cloned such that `ipv6_dest_hao()` calls `pskb_expand_head()`. No local account is required in the network-triggerable scenario. Namespaces are not central to the main risk because the interesting path is packet input processing.

Call-site confidence: **medium-high**. The direct stale pointer refresh site is shown, and the commit explains the `pskb_expand_head()` invalidation mechanism, but the full trailing TLV parsing path and exact crash behavior are not included in the excerpt.

## 4. Severity interpretation

This behaves above an ordinary Moderate because it is a network-reachable IPv6 parser stale pointer issue with a plausible UAF-read style failure. Realistically, the strongest demonstrated impact is remote DoS under specific conditions. Theoretical memory corruption potential exists because stale kernel pointers after skb head relocation are historically dangerous, but the provided patch does not demonstrate an arbitrary write, controlled object reuse, or privilege escalation primitive.

Therefore this should be handled as **Actionable Moderate at minimum**, with **Strong Important candidate** treatment for manual triage because of network reachability plus lifetime corruption.

## 5. One-sentence report phrase

An IPv6 extension header parsing flaw can leave `ip6_parse_tlv()` using a stale network header pointer after HAO handling reallocates skb head storage, allowing a remote crafted packet to cause at least a kernel crash and requiring manual review for limited stale-pointer memory exposure risk.

## 6. Manual review recommendation

**MANUAL CHECK REQUIRED**

Reason: this is a network-reachable IPv6 parser lifetime bug involving a stale skb header pointer after possible `pskb_expand_head()` relocation. The likely impact is DoS, but stale pointer use in packet parsing is sufficiently security-sensitive to avoid auto-closure.

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

Patch: ipv6: exthdrs: refresh nh after handling HAO option
Commit: f8aabed3ff3e986920cf02a2a2785e08e586b234
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f8aabed3ff3e986920cf02a2a2785e08e586b234

Commit description:

ip6_parse_tlv() caches skb_network_header(skb) in nh while walking
IPv6 TLVs.

ipv6_dest_hao() may call pskb_expand_head() for a cloned skb, which can
move the skb head and invalidate the cached network header pointer.
Refresh nh after ipv6_dest_hao() returns so any trailing padding or TLVs
are parsed from the current skb head.

This matches the existing pattern used in ip6_parse_tlv() after helpers
that can modify skb header storage.

Fixes: a831f5b ("[IPV6] MIP6: Add inbound interface of home address option.")
Cc: stable@kernel.org
Reported-by: Yuan Tan <yuantan098@gmail.com>
Reported-by: Xin Liu <bird@lzu.edu.cn>
Co-developed-by: Luxing Yin <tr0jan@lzu.edu.cn>
Signed-off-by: Luxing Yin <tr0jan@lzu.edu.cn>
Signed-off-by: Zhengchuan Liang <zcliangcn@gmail.com>
Signed-off-by: Ren Wei <n05ec@lzu.edu.cn>
Reviewed-by: Justin Iurman <justin.iurman@gmail.com>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Link: https://patch.msgid.link/7aba1debc2196189172499e5769802b026f8caf8.1779247873.git.zcliangcn@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  net/ipv6/exthdrs.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=f8aabed3ff3e986920cf02a2a2785e08e586b234

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

The original Linux kernel CVE announcement for CVE-2026-63922 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63922

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:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/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: 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: IMPORTANT
KPANIC detected for this report: YES
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).