* [CVE-2026-80742][LOW] af_packet: Don't send zero-byte data in tpacket_snd(). [ Upstream
@ 2026-09-03 9:02 21% AL-KERNEL
0 siblings, 0 replies; 1+ results
From: AL-KERNEL @ 2026-09-03 9:02 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-80742
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: af_packet: Don't send zero-byte data in tpacket_snd(). [ Upstream
Commit: dde212f8622f5cb36223fff1ebd6e6f2a3dc61fe
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=dde212f8622f5cb36223fff1ebd6e6f2a3dc61fe
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80742
Analysis date: Thu, 03 Sep 2026 05:02:47 -0400
ActionableScore: 2
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO
Summary:
No one-sentence report phrase was found.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-80742 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80742
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: LOW
Manual review required: NO
A detailed explanation of the methodology and priority rules is included
at the end of this message.
======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================
CVE-2026-80742 LOW https://www.kernelcve.org/list/?q=CVE-2026-80742 CHECK WITH IMPACT FROM ORIG NN MODERATE Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H';*CWE-20;CWE-617;CWE-754;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.5';DESCR 'A local AF_PACKET TPACKET send path can build a zero length skb on devices with no hard header and pass it to packet_xmit. This reaches skb_assert_len in __dev_queue_xmit and triggers a kernel warning. For the CVSS the PR:L is used because triggering requires a local process with AF_PACKET access and typically CAP_NET_RAW or an equivalent delegated packet socket capability. The issue is not network reachable through incoming traffic and requires local code execution. Impact is mainly denial of service. On default systems it may be limited to a warning, but systems configured with panic_on_warn can turn the warning into a kernel crash.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 2) SKIP CVE-2026-80742 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: url YES NO NO unknown MAYBE REMOTE DANGER SKB HARDWARE SYZBOT PACKET DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3 - - checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=2
1. ActionableScore
* Conservative score: 2
* Paranoid score: 2
* Final recommended bucket: **Ordinary Moderate / Low-like**::
2. Signal breakdown
* Local low-privileged trigger: +1. The path is local AF_PACKET/TPACKET send handling and typically requires CAP_NET_RAW or equivalent packet socket capability.
* Availability impact realistic: +1. The demonstrated result is a reachable kernel WARNING in `__dev_queue_xmit()`. On systems with `panic_on_warn`, this can become a kernel crash.
* No memory corruption signal. The patch rejects `skb->len == 0` before transmit. It does not show UAF, OOB write, double free, type confusion, stale callback, or attacker-controlled overwrite.
* No remote/network-triggered signal. Incoming packet traffic does not trigger this path. The attacker must execute local code that uses AF_PACKET/TPACKET.
* No LPE signal. The primitive is a zero-length skb reaching `skb_assert_len()`, not a corruption primitive.
3. Reachability analysis
A local process with AF_PACKET access can trigger the issue by sending a zero-byte packet through a TPACKET ring on a device with no hard header. In typical deployments this requires CAP_NET_RAW, although user namespaces or delegated network capabilities may make this reachable by less trusted local users. The bug is not remotely reachable through normal packet reception. The affected AF_PACKET code is common kernel networking code, but the exact trigger needs local packet-socket access and a suitable device configuration.
4. Severity interpretation
This behaves like a Low to ordinary Moderate local DoS issue. The realistic impact is a WARN and possible crash only on `panic_on_warn` systems. There is no supported evidence of confidentiality impact, integrity impact, memory corruption, or privilege escalation. The issue should not be treated as an Important-class kernel vulnerability based on the supplied patch.
5. One-sentence report phrase
A local AF_PACKET TPACKET sender can create a zero length skb on devices with no hard header, causing `skb_assert_len()` to warn in `__dev_queue_xmit()` and potentially crash systems configured with `panic_on_warn`.
6. Manual review recommendation
NO MANUAL CHECK NEEDED. The patch and call trace show a validation bug leading to a warning or panic-on-warn DoS only, with no concrete memory corruption or privilege escalation primitive.
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: af_packet: Don't send zero-byte data in tpacket_snd(). [ Upstream
Commit: dde212f8622f5cb36223fff1ebd6e6f2a3dc61fe
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=dde212f8622f5cb36223fff1ebd6e6f2a3dc61fe
Changed files:
include/linux/skbuff.h
net/core/dev.c
include/linux/netdevice.h
net/packet/af_packet.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=dde212f8622f5cb36223fff1ebd6e6f2a3dc61fe
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-80742 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80742
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:N/I:N/A:L
The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
The Best / paranoid CVSS score: 5.5
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: unknown
Paranoid ActionableScore: 2
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: LOW
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): LOW
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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