* [CVE-2025-38236][MODERATE 7.0] af_unix: Don't leave consecutive consumed OOB skbs. [ Upstream
@ 2026-09-24 19:59 21% AL-KERNEL
0 siblings, 0 replies; 1+ results
From: AL-KERNEL @ 2026-09-24 19:59 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2025-38236
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: af_unix: Don't leave consecutive consumed OOB skbs. [ Upstream
Commit: a12237865b48a73183df252029ff5065d73d305e
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a12237865b48a73183df252029ff5065d73d305e
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2025-38236
Analysis date: Thu, 24 Sep 2026 15:59:12 -0400
ActionableScore: 5
ActionableScore lower bound: unknown
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES
Summary:
No one-sentence report phrase was found.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2025-38236 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2025-38236
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-2025-38236 MODERATE https://www.kernelcve.org/list/?q=CVE-2025-38236 CHECK WITH IMPACT FROM ORIG NN IMPORTANT Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H';*CWE-416;*CWE-672;*CWE-664;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7.8';DESCR 'A slab use-after-free in the AF_UNIX stream receive path occurs when consecutive consumed OOB skbs remain on the receive queue. The SO_PEEK_OFF traversal can skip zero length consumed skbs, read and free the current OOB skb, and leave the OOB reference pointing to freed memory. A later recv with MSG_OOB dereferences that freed skb and can crash the kernel. For the CVSS the PR:L is selected because any local user able to create an AF_UNIX SOCK_STREAM socket pair can execute the required send and recv sequence without administrative capabilities. The issue is not remotely network reachable because AF_UNIX sockets provide local interprocess communication rather than communication from an external network host. Impact is at least a local denial of service via kernel crash. In the paranoid interpretation the confirmed slab use-after-free may permit confidentiality or integrity impact if the freed skb is reclaimed with attacker influenced data, although the available trace directly demonstrates an invalid read rather than an arbitrary write. Manual review is required to determine whether reliable heap reuse can turn the UAF into privilege escalation.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 5) MAYBE REMOTE READ OOB DANGER UAF SKB KERNEL_PANIC_PLUS_UAF HARDWARE KPANIC DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFDH - - checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=5
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO
1. ActionableScore
* Raw conservative score: 5
* Conservative score: 5
* Raw paranoid score: 5
* Paranoid score: 5
* No floor or cap changed either score.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::
2. Signal breakdown
* +2 Real UAF: an skb is freed by `unix_stream_read_generic()` while `u->oob_skb` continues to reference it, and a later `recv(MSG_OOB)` dereferences the freed object. KASAN confirms a four-byte slab use-after-free read.
* +1 Local unprivileged trigger: an ordinary user can deterministically reach the defect using `socketpair()`, `send()`, and `recv()` without capabilities or administrative access.
* +1 Attacker-influenced active-object lifetime: the same user creates the OOB skbs and drives their consumption, freeing, and subsequent stale use through a repeatable syscall sequence.
* +1 Strong DoS: the post-free kernel access can produce an Oops or panic depending on allocator reuse, hardening, and panic policy. This point is not counted again as a separate Availability impact.
* +0 Structured stale-object leverage: the stale object is an active `sk_buff`, and the receive path consumes its fields, but controlled reclaim or attacker-shaped replacement contents are not demonstrated.
* +0 Strong or weak LPE leverage: no arbitrary write, callback control, refcount takeover, controlled type confusion, or demonstrated privilege escalation is established.
* +0 Confidentiality and integrity: the confirmed operation is an internal four-byte post-free read. No user-visible disclosure or unauthorized kernel modification is shown.
* +0 Remote reachability: AF_UNIX is local IPC and external network traffic cannot directly reach this trigger.
* No negative privilege, race, hardware, or niche-subsystem penalties apply.
* This is not a repeated-release case. The first operation frees the skb, the exact stale reference survives, but the later vulnerable operation reads the object rather than performing a second `put`, `free`, or refcount mutation. The dedicated repeated-release point and FLOOR 5 rule were therefore not applied.
* No paranoid bonus is added merely for theoretical heap reuse.
3. Reachability analysis
The complete trigger is available to an ordinary local user. The reproducer creates an AF_UNIX `SOCK_STREAM` socket pair, sends several `MSG_OOB` records, consumes them in the required order, and invokes the final stale access with another `recv(MSG_OOB)`.
No capability check, namespace-scoped privilege, host-admin operation, prior privileged setup, special hardware, or external device is required. User and network namespaces are irrelevant to reachability because the socket operations are already unprivileged. `CONFIG_AF_UNIX_OOB` must be enabled, but this configuration prerequisite alone does not justify a rarity penalty.
The trigger is an ordered and repeatable syscall sequence rather than a timing race. The attacker directly controls creation and consumption of the affected skbs, although controlled placement of a chosen replacement object at the freed address has not been established.
4. Primitive and severity interpretation
The exact primitive is a slab use-after-free read of an active structured `sk_buff`. Consecutive consumed OOB skbs confuse the `SO_PEEK_OFF` traversal, allowing the current OOB skb to be read and freed while a separate OOB reference remains stale. A later receive operation follows that stale reference.
This is broader than a cleanup-only stale dereference. It occurs in an ordinary active receive path and is deterministically reachable below host-admin privilege. However, the supplied evidence establishes only a four-byte invalid read and potential kernel crash. It does not establish controlled reclaim, arbitrary kernel read or write, disclosure, callback influence, or privilege escalation.
The issue is therefore CLASS_B rather than CLASS_A. `ImportantCandidate=YES` reflects the combination of a genuine active-object UAF, deterministic unprivileged reachability, and unresolved slab-reuse implications. `AutoDowngradeAllowed=NO` is appropriate because automatically treating it as an ordinary crash-only bug could discard meaningful exploitation analysis. The likely operational severity remains Actionable Moderate unless manual analysis demonstrates useful reclaim or another stronger primitive.
5. One-sentence report phrase
An unprivileged local user can trigger a deterministic slab use-after-free in the AF_UNIX OOB receive path, causing a kernel crash and leaving unresolved whether controlled skb slab reuse can provide exploitation leverage beyond denial of service.
6. Manual review recommendation
MANUAL CHECK REQUIRED
The confirmed unprivileged active-object UAF warrants analysis of `skbuff_head_cache` reclaim, the exact stale fields consumed by `unix_stream_read_actor()`, and whether allocations can be interposed between the freeing receive and final stale access.
7. Call-site confidence
Call-site confidence: high
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: af_unix: Don't leave consecutive consumed OOB skbs. [ Upstream
Commit: a12237865b48a73183df252029ff5065d73d305e
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a12237865b48a73183df252029ff5065d73d305e
Changed files:
net/unix/af_unix.c
lib/dump_stack.c
mm/kasan/report.c
net/socket.c
arch/x86/entry/syscall_64.c
arch/x86/entry/entry_64.S
mm/kasan/common.c
include/linux/kasan.h
mm/slub.c
net/core/skbuff.c
include/linux/skbuff.h
net/core/sock.c
include/net/sock.h
mm/kasan/generic.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=a12237865b48a73183df252029ff5065d73d305e
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2025-38236 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2025-38236
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:H
The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
The Best / paranoid CVSS score: 7.8
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: 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: YES
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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