[CVE-2026-80725][IMPORTANT] net: gro: properly validate BIG TCP aggregation criteria When GRO attempts to aggregate IPv6 packets beyond GRO_LEGACY_MAX_SIZE (64KB), the aggregate should only be permitted for plain IPv6 TCP flows that have sufficient MAC header room to insert the temporary HBH jumbo header. In 6.1.y, skb_gro_receive() had two issues with this check: 1. It checked skb_headroom(p) instead of the actual space before the MAC header (p->mac_header). Because skb_headroom(p) measures (data - head), it includes mac_len. Crafted frames (e.g. injected via AF_PACKET) can pass the check with p->mac_header < 8 bytes. When ipv6_gro_complete() inserts the temporary HBH jumbo header, the memmove() starts before skb->head, causing an out-of-bounds write and wrapping skb->mac_header. 2. It checked p->encapsulation instead of NAPI_GRO_CB(skb)->encap_mark, which is 0 during receive, failing to reject encapsulated IPv6 flows (such as IP6IP6). Fix skb_gro_receive() to strictly check: - p->protocol == htons(ETH_P_IPV6) - p->mac_header >= sizeof(struct hop_jumbo_hdr) - ipv6_hdr(p)->nexthdr == IPPROTO_TCP - Not encapsulated (!NAPI_GRO_CB(skb)->encap_mark && !p->encapsulation) Returning -E2BIG from skb_gro_receive() ensures that packets which cannot become BIG TCP are cleanly flushed at <= 64KB and delivered intact without dropping. This issue does not exist in mainline (7.0+) because the subsystem was rewritten in

[CVE-2026-80725][IMPORTANT] net: gro: properly validate BIG TCP aggregation criteria When GRO attempts to aggregate IPv6 packets beyond GRO_LEGACY_MAX_SIZE (64KB), the aggregate should only be permitted for plain IPv6 TCP flows that have sufficient MAC header room to insert the temporary HBH jumbo header. In 6.1.y, skb_gro_receive() had two issues with this check: 1. It checked skb_headroom(p) instead of the actual space before the MAC header (p->mac_header). Because skb_headroom(p) measures (data - head), it includes mac_len. Crafted frames (e.g. injected via AF_PACKET) can pass the check with p->mac_header < 8 bytes. When ipv6_gro_complete() inserts the temporary HBH jumbo header, the memmove() starts before skb->head, causing an out-of-bounds write and wrapping skb->mac_header. 2. It checked p->encapsulation instead of NAPI_GRO_CB(skb)->encap_mark, which is 0 during receive, failing to reject encapsulated IPv6 flows (such as IP6IP6). Fix skb_gro_receive() to strictly check: - p->protocol == htons(ETH_P_IPV6) - p->mac_header >= sizeof(struct hop_jumbo_hdr) - ipv6_hdr(p)->nexthdr == IPPROTO_TCP - Not encapsulated (!NAPI_GRO_CB(skb)->encap_mark && !p->encapsulation) Returning -E2BIG from skb_gro_receive() ensures that packets which cannot become BIG TCP are cleanly flushed at <= 64KB and delivered intact without dropping. This issue does not exist in mainline (7.0+) because the subsystem was rewritten in

[AL-KERNEL]

CVE: CVE-2026-80725
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: net: gro: properly validate BIG TCP aggregation criteria When GRO attempts to aggregate IPv6 packets beyond GRO_LEGACY_MAX_SIZE (64KB), the aggregate should only be permitted for plain IPv6 TCP flows that have sufficient MAC header room to insert the temporary HBH jumbo header. In 6.1.y, skb_gro_receive() had two issues with this check: 1. It checked skb_headroom(p) instead of the actual space before the MAC header (p->mac_header). Because skb_headroom(p) measures (data - head), it includes mac_len. Crafted frames (e.g. injected via AF_PACKET) can pass the check with p->mac_header < 8 bytes. When ipv6_gro_complete() inserts the temporary HBH jumbo header, the memmove() starts before skb->head, causing an out-of-bounds write and wrapping skb->mac_header. 2. It checked p->encapsulation instead of NAPI_GRO_CB(skb)->encap_mark, which is 0 during receive, failing to reject encapsulated IPv6 flows (such as IP6IP6). Fix skb_gro_receive() to strictly check: - p->protocol == htons(ETH_P_IPV6) - p->mac_header >= sizeof(struct hop_jumbo_hdr) - ipv6_hdr(p)->nexthdr == IPPROTO_TCP - Not encapsulated (!NAPI_GRO_CB(skb)->encap_mark && !p->encapsulation) Returning -E2BIG from skb_gro_receive() ensures that packets which cannot become BIG TCP are cleanly flushed at <= 64KB and delivered intact without dropping. This issue does not exist in mainline (7.0+) because the subsystem was rewritten in
Commit: 37a5dcd6837fc2afc44a7bc3ed8af4e983783d46
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=37a5dcd6837fc2afc44a7bc3ed8af4e983783d46
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80725
Analysis date: Sat, 29 Aug 2026 02:52:38 -0400
ActionableScore: 8
ActionableScore lower bound: 6
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
BIG TCP GRO validation could allow invalid large packet aggregation with insufficient MAC header space, causing ipv6_gro_complete to perform a memmove before skb head and trigger kernel memory corruption, with local AF_PACKET or adjacent network reachability depending on configuration.

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

The original Linux kernel CVE announcement for CVE-2026-80725 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80725

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-2026-80725	IMPORTANT	CHECK WITH IMPACT FROM ORIG NN IMPORTANT	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-787;*CWE-20;CWE-119;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7.5';DESCR 'BIG TCP GRO aggregation can accept packets above 64KB without fully validating the protocol, encapsulation state, and available MAC header space. For IPv6 this can make ipv6_gro_complete insert a temporary jumbo HBH header when p mac_header is too small, causing a memmove before skb head and an out of bounds write. A reliable trigger is described through crafted frames such as AF_PACKET injection, while a network adjacent trigger may be possible on affected RX GRO paths when BIG TCP is enabled. For the CVSS the PR:N is used for the paranoid score because an adjacent sender may not need a local account if the vulnerable RX path is reachable through L2 traffic. Impact is at least denial of service via kernel crash and in worst case may allow confidentiality or integrity impact because the primitive is kernel memory corruption, not only a NULL dereference or resource leak. The issue is not rated as AV:N because practical exposure is normally limited to local or adjacent network paths and specific BIG TCP configuration.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 8)	YES	REMOTE WRITE OOB SKB LINUS IPV6 KPANIC PACKET 	YES	NO	guess

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

ActionableScore=8
ActionableScoreLower=6

## 1. ActionableScore

* Conservative score: **6**
* Paranoid score: **8**
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

### Conservative score: 6

* **Local low-privilege or delegated trigger: +1**
  The commit explicitly mentions crafted frames injected via `AF_PACKET`. This is local and usually requires `CAP_NET_RAW`, but in some namespace or container configurations this may be reachable by non-root or reduced-privilege users.

* **Memory corruption, strong corruption primitive: +2**
  The patch description explicitly states that `ipv6_gro_complete()` may perform a `memmove()` before `skb->head`, causing an out-of-bounds write and wrapping `skb->mac_header`.

* **Memory layout invariant restoration: +1**
  The fix restores consistency between BIG TCP aggregation criteria, protocol type, encapsulation state, and available MAC-header space.

* **Reliable kernel crash / strong DoS: +1**
  An OOB write in the GRO receive path can realistically crash the kernel.

* **Common networking core path or packet-processing path: +1**
  `skb_gro_receive()` is in the core GRO packet aggregation path.

* **Confidentiality and integrity impact plausible: +2**
  Because the primitive is an actual kernel OOB write, not only a NULL dereference or warning, C/I impact cannot be excluded for triage.

* **Legacy / non-default execution mode: -1**
  The issue is relevant to older stable branches such as 6.18.y and requires BIG TCP style GRO aggregation above 64KB.

* **Constrained or partially kernel-derived overwrite: -1**
  The write appears to be caused by internal header movement rather than an obviously attacker-selected arbitrary write target or arbitrary payload.

### Paranoid score: 8

* **Network-triggerable or adjacent-network trigger: +2**
  A network-adjacent trigger is technically defensible because the bug is in RX GRO packet processing and may be reachable through L2 or local-network traffic when BIG TCP is enabled. This should not be treated as broad Internet AV:N exposure.

* **Memory corruption, strong corruption primitive: +2**
* **Memory layout invariant restoration: +1**
* **Reliable kernel crash / strong DoS: +1**
* **Common networking core path or packet-processing path: +1**
* **Confidentiality impact plausible: +1**
* **Integrity impact plausible: +1**
* **Legacy / non-default execution mode: -1**
* **Constrained overwrite uncertainty: -1**

Total paranoid score: **8**

## 3. Reachability analysis

The most concrete trigger described is local crafted-frame injection through `AF_PACKET`, which normally requires `CAP_NET_RAW` but may be available inside user namespaces or delegated container environments. A more paranoid interpretation treats this as adjacent-network reachable because the vulnerable code is in the GRO RX path and the invalid aggregation state may be influenced by received L2 traffic when BIG TCP is configured.

This is not a generic remote Internet vulnerability. Practical exposure depends on affected older stable kernels, GRO being active, BIG TCP or large `gro_max_size` behavior being enabled, and traffic reaching the vulnerable aggregation path. The issue does not exist in mainline 7.0+ according to the commit message because the relevant BIG TCP RX-side behavior was rewritten.

Call-site confidence: **high**, because the patch and commit directly identify `skb_gro_receive()` and the later `ipv6_gro_complete()` OOB write consequence.

## 4. Severity interpretation

This is stronger than an ordinary Moderate issue because the patch context explicitly describes an out-of-bounds write before `skb->head` in a core networking buffer path. Realistic exploitation may still be difficult because the trigger depends on BIG TCP conditions and likely local or adjacent-network positioning rather than broad remote reachability.

Conservatively, this is an **Actionable Moderate** issue that should not be auto-closed. Paranoid triage makes it a **Strong Important candidate**, mainly because kernel memory corruption in GRO packet processing has historically been under-scored when early analysis focuses only on crash symptoms.

## 5. One-sentence report phrase

BIG TCP GRO validation could allow invalid large packet aggregation with insufficient MAC header space, causing ipv6_gro_complete to perform a memmove before skb head and trigger kernel memory corruption, with local AF_PACKET or adjacent network reachability depending on configuration.

## 6. Manual review recommendation

**MANUAL CHECK REQUIRED**

Reason: the patch explicitly describes an out-of-bounds write in a core networking receive path, with possible local crafted-frame triggering and defensible adjacent-network exposure. YES REQUIRES MANUAL CHECK.

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

Patch: net: gro: properly validate BIG TCP aggregation criteria When GRO attempts to aggregate IPv6 packets beyond GRO_LEGACY_MAX_SIZE (64KB), the aggregate should only be permitted for plain IPv6 TCP flows that have sufficient MAC header room to insert the temporary HBH jumbo header. In 6.1.y, skb_gro_receive() had two issues with this check: 1. It checked skb_headroom(p) instead of the actual space before the MAC header (p->mac_header). Because skb_headroom(p) measures (data - head), it includes mac_len. Crafted frames (e.g. injected via AF_PACKET) can pass the check with p->mac_header < 8 bytes. When ipv6_gro_complete() inserts the temporary HBH jumbo header, the memmove() starts before skb->head, causing an out-of-bounds write and wrapping skb->mac_header. 2. It checked p->encapsulation instead of NAPI_GRO_CB(skb)->encap_mark, which is 0 during receive, failing to reject encapsulated IPv6 flows (such as IP6IP6). Fix skb_gro_receive() to strictly check: - p->protocol == htons(ETH_P_IPV6) - p->mac_header >= sizeof(struct hop_jumbo_hdr) - ipv6_hdr(p)->nexthdr == IPPROTO_TCP - Not encapsulated (!NAPI_GRO_CB(skb)->encap_mark && !p->encapsulation) Returning -E2BIG from skb_gro_receive() ensures that packets which cannot become BIG TCP are cleanly flushed at <= 64KB and delivered intact without dropping. This issue does not exist in mainline (7.0+) because the subsystem was rewritten in
Commit: 37a5dcd6837fc2afc44a7bc3ed8af4e983783d46
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=37a5dcd6837fc2afc44a7bc3ed8af4e983783d46

Changed files:
  net/core/gro.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=37a5dcd6837fc2afc44a7bc3ed8af4e983783d46

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

The original Linux kernel CVE announcement for CVE-2026-80725 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80725

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: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: 8

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).