[CVE-2026-98095][LOW] af_packet: Don't cast tpacket_hdr.tp_len to int in tpacket_parse_header(). [ Upstream

[AL-KERNEL <alkernel@kernelcve.org>]

CVE: CVE-2026-98095
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: af_packet: Don't cast tpacket_hdr.tp_len to int in tpacket_parse_header(). [ Upstream
Commit: c6b3db727876a027013aa4ccb6913a153a2af41a
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c6b3db727876a027013aa4ccb6913a153a2af41a
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98095
Analysis date: Fri, 25 Sep 2026 14:41:48 -0400
ActionableScore: 0
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-98095 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98095

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-2026-98095	LOW	https://www.kernelcve.org/list/?q=CVE-2026-98095 CHECK WITH IMPACT FROM ORIG NN LOW	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-681;*CWE-20;CWE-190;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 signed integer conversion flaw in AF_PACKET allows the user controlled u32 tpacket_hdr.tp_len value to become a negative int inside tpacket_parse_header. A value larger than INT_MAX can bypass the intended maximum length check and propagate a negative internal return value to sock_sendmsg_nosec. A specially selected value can be interpreted as -EIOCBQUEUED and trigger a kernel BUG, resulting in an Oops or a kernel panic and denial of service. For the CVSS the PR:L reflects that a local process must create and configure an AF_PACKET TX ring, which normally requires CAP_NET_RAW but may be delegated to a reduced capability process or a configured namespace user. The issue is not remotely reachable through packet traffic because local control of the memory mapped ring header and a local write operation are required. The demonstrated primitive is an invalid signed return value rather than a UAF, OOB access, or arbitrary write. Impact is limited to availability, with A:H used for the paranoid score when BUG handling or panic_on_oops causes a system wide crash.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 0) 	MAYBE	REMOTE READ KASAN 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=0
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: 0
* Conservative score: 0
* Raw paranoid score: 0
* Paranoid score: 0
* No floor or cap was applied.
* Final recommended bucket: **Ordinary Moderate**::

2. Signal breakdown

* +1 Reliable kernel crash or strong DoS. A crafted `tp_len` is demonstrated to reach `sock_sendmsg_nosec()` as `-EIOCBQUEUED` and trigger `BUG()`. Depending on kernel policy, this produces an Oops or panic.
* -1 Reduced or delegated privilege. Creating the required AF_PACKET socket and TX ring requires `CAP_NET_RAW`, which is narrower than host-admin-equivalent privilege and can be delegated.
* No additional Availability point. It would duplicate the same demonstrated `BUG()` consequence.
* No corruption point. The primitive is an invalid signed return value, not an OOB access, UAF, overwrite, stale pointer, or lifetime violation.
* No local-unprivileged bonus. Ordinary-user access to the complete path depends on namespace policy or explicit `CAP_NET_RAW` delegation and is not established by the supplied evidence.
* No remote-reachability bonus. Network packets alone cannot prepare the memory-mapped TX-ring header and issue the required local write.
* No confidentiality, integrity, LPE, controlled-reclaim, arbitrary-write, or semantic-reinterpretation signal is established.
* No race or timing penalty applies because the trigger is deterministic.

3. Reachability analysis

The attacker must locally create an AF_PACKET socket, configure a packet TX ring, place an oversized `u32` value in `tpacket_hdr.tp_len`, and invoke the local write path. AF_PACKET socket creation requires `CAP_NET_RAW`, but this capability does not inherently provide host-admin-equivalent control, so `HostAdminRequired=NO`.

The capability check is associated with the relevant network namespace, but the supplied evidence does not establish that an ordinary attacker can create all required namespaces and obtain the capability under the evaluated system policy. Therefore, `NamespaceScopedPrivilege=UNKNOWN`. Explicit capability delegation or enabled unprivileged user namespaces may provide reachability, while restrictive deployments may require prior privileged setup.

No special hardware, boot mode, race, or remotely supplied packet sequence is required.

4. Primitive and severity interpretation

The exact primitive is a `u32` to `int` conversion that turns a length above `INT_MAX` into a negative value. This bypasses the intended upper-bound check and allows a selected internal error value to propagate into a caller that treats `-EIOCBQUEUED` as an impossible result and executes `BUG()`.

This is Class C invalid-state and crash behavior. It is not a UAF, repeated release, memory overwrite, information disclosure, or authorization bypass. The demonstrated consequence is local denial of service through an Oops or kernel panic. Stronger consequences would require an additional primitive not supported by the patch or call trace.

`ImportantCandidate=NO` because no independently useful corruption or boundary-bypass mechanism remains after excluding the crash. `AutoDowngradeAllowed=YES` because the behavior is deterministic but constrained to invalid return-value propagation and availability impact.

5. One-sentence report phrase

A CAP_NET_RAW process can place an oversized length in an AF_PACKET TX ring so that signed conversion propagates a crafted negative return value to sock_sendmsg_nosec and triggers a kernel BUG, with no demonstrated memory corruption or remote trigger.

6. Manual review recommendation

NO MANUAL CHECK NEEDED

The patch and trace establish a bounded local crash-only condition without UAF, OOB access, arbitrary write, disclosure, privilege escalation, or unresolved security-boundary impact.

7. Call-site confidence

Call-site confidence: high

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

Patch: af_packet: Don't cast tpacket_hdr.tp_len to int in tpacket_parse_header(). [ Upstream
Commit: c6b3db727876a027013aa4ccb6913a153a2af41a
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c6b3db727876a027013aa4ccb6913a153a2af41a

Changed files:
  net/socket.c
  fs/read_write.c
  arch/x86/entry/syscall_64.c
  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=c6b3db727876a027013aa4ccb6913a153a2af41a

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

The original Linux kernel CVE announcement for CVE-2026-98095 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98095

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: 0

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