* [CVE-2026-80731][MODERATE 7.0] Revert "net: validate variable length ll headers" This reverts commit b551842 , which was
@ 2026-09-03 9:30 21% AL-KERNEL
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From: AL-KERNEL @ 2026-09-03 9:30 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-80731
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: Revert "net: validate variable length ll headers" This reverts commit b551842 , which was
Commit: 53fd7f912c0877647d6a1e1877f5ea8535ee0b4a
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=53fd7f912c0877647d6a1e1877f5ea8535ee0b4a
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80731
Analysis date: Thu, 03 Sep 2026 05:30:40 -0400
ActionableScore: 5
ActionableScore lower bound: 3
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES
Summary:
No one-sentence report phrase was found.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-80731 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80731
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-2026-80731 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-80731 CHECK WITH IMPACT FROM ORIG NN MODERATE 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-787;CWE-362;CWE-119;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'dev_validate_header could zero pad a short link layer header using a later and larger dev hard_header_len than the value used when skb headroom was reserved. A concurrent device reconfiguration can therefore turn the CAP_SYS_RAWIO zero padding path into an out-of-bounds write past the reserved packet buffer. For the CVSS the PR:L is used in the paranoid score because CAP_SYS_RAWIO may be delegated to a reduced capability root or service account even though the normal base case is PR:H. The issue is local and is not directly network reachable because the trigger requires local packet send control and a timing race with device configuration changes. Impact is at least denial of service and in worst case may allow confidentiality or integrity impact because the primitive is a kernel out-of-bounds write, so manual review is required.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 4) SKIP CVE-2026-80731 UNKNOWN SKIP No affected files built, so skip this CVE NO - - unknown MAYBE WRITE OOB DANGER HARDWARE TEST PACKET INCREASED_TO_HIGH_BASED_ON_GUESSCVSS DECREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCORELOWERTHAN5 DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5 - - checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=5
ActionableScoreLower=3
1. ActionableScore
Conservative score: 3
Paranoid score: 5
Final recommended bucket: **Actionable Moderate at minimum**::
2. Signal breakdown
Conservative signals:
- +1 Constrained kernel buffer overwrite. The write is an out-of-bounds memset past skb reserved headroom, but the payload is zero-filled and target control appears limited.
- +1 Memory layout invariant restoration. The bug comes from inconsistent use of dev->hard_header_len between skb headroom allocation and later validation.
- +1 Reliable kernel crash / strong DoS. The commit explicitly mentions skb_under_panic in some paths and an OOB write in others.
- +1 Common networking core / packet send path. dev_validate_header() is a networking helper used from packet send paths, although this specific branch is narrow.
- +1 Privileged kernel/device-management memory corruption path. The issue depends on netdevice reconfiguration and trusted skb/header handling.
- -1 Hard or unreliable race / special timing required. Triggering requires hard_header_len to grow between allocation and validation.
- -2 Requires CAP_SYS_RAWIO in typical deployments. The removed branch is explicitly gated by capable(CAP_SYS_RAWIO).
Paranoid additional interpretation:
- +1 Weak LPE concern. The primitive is a kernel OOB write, so limited privilege escalation concern is defensible for manual triage even though no controlled payload or reclaim primitive is shown.
- +1 Confidentiality impact plausible. Worst-case memory corruption could affect adjacent kernel data, but no disclosure primitive is demonstrated.
- +1 Integrity impact plausible. The OOB write can corrupt kernel memory, although with zero payload and constrained placement.
3. Reachability analysis
The realistic trigger is local and privileged because the vulnerable zero-padding branch requires CAP_SYS_RAWIO. A practical scenario also needs local packet send control, a short variable-length L2 header, and concurrent netdevice reconfiguration that increases dev->hard_header_len between skb headroom allocation and dev_validate_header(). This is not directly network reachable. Namespace or container setups may matter if CAP_SYS_RAWIO is delegated to a reduced-capability root, container root, or service account, but typical host deployments treat this as privileged local access. Call-site confidence: medium-high, because the commit describes the relevant packet send path behavior and the exact allocation-versus-validation mismatch.
4. Severity interpretation
This is not an ordinary DoS-only bug because the patch context explicitly describes an out-of-bounds write. It is also not a clear Important-class LPE because the overwrite is zero-filled, timing-dependent, CAP_SYS_RAWIO-gated, and lacks demonstrated target selection, reclaim, type confusion, or arbitrary write. Conservative handling is borderline manual-review Moderate. Paranoid handling reaches Actionable Moderate because kernel memory corruption in a networking skb path can be underestimated and should not be auto-closed without review.
5. One-sentence report phrase
dev_validate_header() could zero-pad a short link-layer header using a later enlarged dev->hard_header_len, allowing a CAP_SYS_RAWIO local actor racing netdevice reconfiguration to trigger a constrained skb out-of-bounds write and possible kernel crash or memory corruption.
6. Manual review recommendation
MANUAL CHECK REQUIRED
Reason: the bug has a concrete kernel OOB write primitive in a networking packet path, even though the realistic trigger is privileged, race-dependent, and constrained.
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: Revert "net: validate variable length ll headers" This reverts commit b551842 , which was
Commit: 53fd7f912c0877647d6a1e1877f5ea8535ee0b4a
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=53fd7f912c0877647d6a1e1877f5ea8535ee0b4a
Commit description:
It is
pointless unless af_packet calls the new function.
Signed-off-by: Ben Hutchings <[email protected]>
Changed files:
include/linux/netdevice.h
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=53fd7f912c0877647d6a1e1877f5ea8535ee0b4a
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-80731 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80731
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:H/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: 3
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: MODERATE
KPANIC detected for this report: NO
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 [email protected] (and both
send reply to CVE record itself too and see "reply" button below for howto reply).
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