[CVE-2026-68144][IMPORTANT] phonet: pep: fix use-after-free in pep_get_sb()

[CVE-2026-68144][IMPORTANT] phonet: pep: fix use-after-free in pep_get_sb()

[AL-KERNEL]

CVE: CVE-2026-68144
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: phonet: pep: fix use-after-free in pep_get_sb()
Commit: 8d931a75a38b9bb584a4071f5ebbd52755fc35ee
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=8d931a75a38b9bb584a4071f5ebbd52755fc35ee
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68144
Analysis date: Mon, 10 Aug 2026 16:13:26 -0400
ActionableScore: 7
ActionableScore lower bound: 4
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A use-after-free in the Phonet PEP receive path occurs because pep_get_sb() reuses an skb header pointer after pskb_may_pull() may relocate the skb head, allowing crafted Phonet traffic to crash the kernel and potentially creating a constrained memory corruption primitive.

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

The original Linux kernel CVE announcement for CVE-2026-68144 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68144

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
======================================================================

CVE-2026-68144	IMPORTANT	CHECK WITH IMPACT FROM ORIG NN MODERATE	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-416;CWE-825;*CWE-787;Other CVSS 'AV:A/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:H';BEST CVSS score: '7.5';DESCR 'A use after free in the Phonet PEP receive path occurs because pep_get_sb() keeps using an skb header pointer after pskb_may_pull() may have reallocated the skb head. The stale pointer is then used for reads and for updating sb_len, so the bug is a memory corruption candidate rather than a simple NULL pointer dereference. A crafted Phonet PEP packet can trigger a kernel crash and may have higher impact if the freed slab object can be influenced. For the CVSS the PR:N because the paranoid network adjacent scenario assumes the attacker can deliver crafted Phonet traffic to a reachable Phonet interface without local privileges on the victim. The issue is not Internet routable in typical deployments and is more likely limited to local or adjacent modem, virtual device, or specialized Phonet networks. Impact is at least denial of service via kernel crash and in the paranoid case may include confidentiality and integrity impact due to use after free memory corruption.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 6)  SKIP CVE-2026-68144 UNKNOWN SKIP No affected files built, so skip this CVE NO  - - unknown 	MAYBE	READ DANGER UAF SKB LINUS  KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=7
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: 4
* Paranoid score: 7
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Remote reachable / network-triggerable: +2. The bug is in the Phonet receive path and can be triggered by crafted Phonet PEP traffic if a reachable Phonet interface exists.
* Generic memory corruption, strong corruption primitive: +2. The commit explicitly reports KASAN slab-use-after-free in pep_get_sb().
* Real lifetime corruption: +1. The stale skb header pointer survives pskb_may_pull(), which may reallocate the skb head.
* Reliable kernel crash / strong DoS: +1. KASAN reproduces a slab-use-after-free in the receive path.
* Rare AND difficult-to-reach subsystem/configuration: -1. Phonet is a specialized protocol and is not broadly Internet exposed.
* No attacker-controlled payload or overwrite target: -1. The visible write is constrained to ph->sb_len -= 2 through a stale pointer, without a demonstrated controlled reclaim or arbitrary target.

Paranoid additional signals:

* Weak LPE concern: +1. The stale pointer is not only read but also written through ph->sb_len -= 2, making this more concerning than a read-only stale dereference.
* Confidentiality impact plausible: +1. UAF reuse could theoretically expose stale or misinterpreted kernel data, although no disclosure primitive is shown.
* Integrity impact plausible: +1. The stale write into freed slab memory creates a plausible integrity concern, but without demonstrated control.

Not awarded:

* Strong LPE plausibility: +0. No attacker-controlled reclaim, object replacement, callback control, type confusion, or reliable overwrite primitive is demonstrated.
* Common networking core path: +0. This is a network receive path, but Phonet is niche and not comparable to TCP/IP, netfilter, or common skb core handling.
* Hard race penalty: +0. This is not primarily a race. The trigger depends on skb relocation by pskb_may_pull(), but not on winning a narrow concurrent timing window.

Call-site confidence: high. The provided stack and function context show pep_get_sb() called from the Phonet receive path and the stale pointer use occurs immediately after pskb_may_pull().

## 3. Reachability analysis

An attacker needs the ability to deliver crafted Phonet PEP traffic to a reachable Phonet interface. In CVSS-like terms this is best treated as network-adjacent rather than Internet-wide remote exposure. Phonet is uncommon in typical server and desktop deployments and is more likely relevant on systems with modem, virtual, or specialized Phonet networking support.

No local privileges on the victim are required in the paranoid network-adjacent model if crafted traffic can be delivered externally. Namespace behavior is not the main factor here. The main practical limiting factors are whether Phonet is enabled, whether an interface is present, and whether the attacker can reach that interface.

## 4. Severity interpretation

This is not an ordinary Moderate NULL-dereference issue. It is a confirmed UAF in a packet receive path, and the stale pointer is used after a possible skb head relocation. Realistic demonstrated impact is kernel crash / DoS. Theoretical impact is higher because the code also writes through the stale pointer, but the patch does not show controlled reclaim, object replacement, or an arbitrary write primitive.

Conservatively this is a borderline manual-review issue with ActionableScore 4. Paranoid scoring reaches 7 because it combines network-adjacent reachability, real UAF lifetime corruption, and a constrained stale write in kernel networking code. This makes it a Strong Important candidate for manual triage, even though practical exploitation beyond DoS is not demonstrated.

## 5. One-sentence report phrase

A use-after-free in the Phonet PEP receive path occurs because pep_get_sb() reuses an skb header pointer after pskb_may_pull() may relocate the skb head, allowing crafted Phonet traffic to crash the kernel and potentially creating a constrained memory corruption primitive.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED.

Reason: confirmed KASAN UAF in a network receive path, with a stale pointer write candidate and possible network-adjacent triggerability, even though exploitation beyond DoS is not proven.

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

Patch: phonet: pep: fix use-after-free in pep_get_sb()
Commit: 8d931a75a38b9bb584a4071f5ebbd52755fc35ee
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=8d931a75a38b9bb584a4071f5ebbd52755fc35ee

Commit description:

pep_get_sb() doesn't consider that pskb_may_pull() might have relocated
the skb data, and continue to access the older pointer, causing UAF.

Reproduced under KASAN:

  BUG: KASAN: slab-use-after-free in pep_get_sb+0x234/0x3b0
  Read of size 1 at addr ff11000105510f50 by task repro/157
   pep_get_sb+0x234/0x3b0
   pipe_handler_do_rcv+0x5f7/0xa10
   pep_do_rcv+0x203/0x410
   __sk_receive_skb+0x471/0x4a0
   phonet_rcv+0x5b3/0x6c0
   __netif_receive_skb+0xcc/0x1d0

Refetch the header with skb_header_pointer() after pskb_may_pull(), so
the possibly stale pointer is no longer dereferenced. There are better
ways to solve this, but, this is the less instrusive one.

Fixes: 9641458 ("Phonet: Pipe End Point for Phonet Pipes protocol")
Cc: stable@vger.kernel.org
Signed-off-by: Breno Leitao <leitao@debian.org>
Link: https://patch.msgid.link/20260721-phonet_get_sb_uaf-v1-1-95fd7881cc4e@debian.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  net/phonet/pep.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=8d931a75a38b9bb584a4071f5ebbd52755fc35ee

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

The original Linux kernel CVE announcement for CVE-2026-68144 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68144

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:A/AC:H/PR:N/UI:N/S:U/C:N/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: 4
  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).