[CVE-2026-98276][MODERATE 7.0] net: lock the socket in sock_gettstamp() [ Upstream

[CVE-2026-98276][MODERATE 7.0] net: lock the socket in sock_gettstamp() [ Upstream

[AL-KERNEL]

CVE: CVE-2026-98276
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: net: lock the socket in sock_gettstamp() [ Upstream
Commit: 18899e2e4023369a8f7739c2255a59a9748d8d17
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=18899e2e4023369a8f7739c2255a59a9748d8d17
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98276
Analysis date: Sat, 10 Oct 2026 17:18:37 -0400
ActionableScore: 6
ActionableScore lower bound: 5
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES

Summary:
An unprivileged local user can race UDP bind with a timestamp ioctl to clear SOCK_RCU_FREE, causing premature socket destruction and a confirmed use-after-free in the IPv4 UDP receive path with kernel crash potential and unresolved post-free exploitation leverage.

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

The original Linux kernel CVE announcement for CVE-2026-98276 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98276

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-2026-98276	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-98276 CHECK WITH IMPACT FROM ORIG NN MODERATE | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=4 LEGACY=MODERATE_KPANIC RESULT=SAME (legacy and Aegis reconciliation agree; DECISION: both MODERATE_KPANIC)	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-362;*CWE-416;CWE-667;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'A race in sock_gettstamp can cause a lost update in sk_flags because SOCK_TIMESTAMP is set without holding the socket lock while UDP bind may concurrently set SOCK_RCU_FREE. The lost SOCK_RCU_FREE bit allows sk_destruct to free a UDP socket without waiting for an RCU grace period even though the socket is already visible to lockless receive lookups. This produces a confirmed slab use-after-free in the IPv4 UDP receive path and can at least cause a kernel crash. For the CVSS the PR:L value is used because an unprivileged local user can create the UDP socket and invoke bind and SIOCGSTAMPNS_NEW without administrative capabilities. AC:H is used because reliable triggering requires winning a race between the ioctl and bind operations and reaching the receive path during the resulting lifetime violation. The issue is not independently network reachable because remote packets alone cannot arrange the local syscall race, although network traffic can activate the affected receive path. Impact is at least local denial of service and may include confidentiality or integrity impact due to reuse of the prematurely freed socket object. Privilege escalation is plausible for the paranoid assessment because the confirmed UAF affects a kernel heap object reachable from a lockless path, but a reliable arbitrary write primitive is not established by the available code.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 6)	MAYBE	REMOTE READ DANGER UAF HARDWARE LINUS KPANIC  KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFKP	-	-	checked

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ACTIONABLESCORE ANALYSIS
======================================================================

ActionableScore=6
ActionableScoreLower=5
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO
RequiresHostUID0=NO
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO

## 1. ActionableScore

* Raw conservative score: 5
* Conservative score: 5
* Raw paranoid score: 6
* Paranoid score: 6
* No floor or cap changed either score. The real-UAF floor of 5 was checked and already satisfied by the conservative arithmetic.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::

## 2. Signal breakdown

Conservative positive signals:

* +2 Real UAF and lifetime violation. Loss of `SOCK_RCU_FREE` permits `sk_destruct()` to free the socket while lockless UDP receive processing still holds a reference-less pointer.
* +1 Local unprivileged trigger. The supplied KASAN trace identifies an exploit process running as UID 1000, and the trigger uses ordinary UDP socket operations, `bind()`, and `SIOCGSTAMPNS_NEW`.
* +1 Reliable kernel crash or strong DoS. A slab use-after-free is demonstrated in `ipv4_pktinfo_prepare()` and can result in an Oops or kernel crash outside diagnostic builds.
* +1 Common networking packet-processing path. The stale socket reaches the normal IPv4 UDP receive path rather than a diagnostic or teardown-only consumer.

Paranoid additional signal:

* +1 Attacker-influenced active-object lifetime manipulation. The same unprivileged actor controls socket creation and can repeatedly drive the competing `bind()` and timestamp-ioctl operations, then exercise the receive path. This supports unresolved reuse analysis, although controlled reclaim is not demonstrated.

Important non-awarded signals:

* +2 strong exploitation leverage was not awarded. Controlled reclaim, attacker-shaped replacement contents, callback control, and arbitrary kernel read or write are not demonstrated.
* Structured stale-object leverage was not separately awarded. The stale receive path consumes an active `struct sock`, but the evidence does not yet establish useful field consumption after attacker-controlled replacement.
* Confidentiality and integrity points were not awarded merely because heap reuse is theoretically possible.
* No extra Availability point was awarded because the same UAF-induced crash is already counted once.
* No race penalty was applied. Both competing operations are attacker-driven and attempts are cheap and repeatable. The evidence does not establish a one-shot or externally uncontrollable race.
* No remote-reachability bonus was awarded. Packets exercise the stale receive path, but remote traffic alone cannot arrange the local `bind()` versus ioctl race.
* No RCU referenced-object mismatch point was awarded because this is direct premature destruction of the RCU-visible socket, not the separate container-A-to-object-B lifetime pattern required by that rule.
* No repeated-release or refcount point applies. There is no demonstrated first release followed by a second lifetime-mutating release on the exact same dangling reference.
* B5-R does not apply because there is no retry-accumulated heap OOB write.
* B3-PENDING does not apply because no shared-backing or file-backed write is involved.
* B4-PENDING does not apply because this is not an authorization decision bypass.

## 3. Reachability analysis

An ordinary local user can create the UDP socket and invoke both `bind()` and `SIOCGSTAMPNS_NEW`. The supplied report confirms execution under UID 1000, so host-administrator powers and host UID 0 are not required.

No capability or namespace-scoped privilege is needed for the relevant operations. Consequently, the complete trigger is below host-admin privilege rather than dependent on delegated `CAP_NET_ADMIN`.

The attacker controls both sides of the race and can recreate sockets for repeated attempts. Packet delivery is needed to enter the UDP receive path after publication, but this can be arranged through ordinary networking, including locally generated traffic. Remote packets by themselves are insufficient because the attacker must also perform the local syscall race.

No special hardware, uncommon boot option, privileged subsystem setup, or prior host-administrator configuration is established as necessary.

## 4. Primitive and severity interpretation

The exact primitive is a lost non-atomic update to `sk_flags`. Concurrent read-modify-write operations can erase `SOCK_RCU_FREE` while preserving `SOCK_TIMESTAMP`. The socket is then published for lockless UDP lookup without the flag that would defer destruction through an RCU grace period.

This creates a real post-lifetime read of an active structured kernel object in ordinary packet processing. It is broader than a cleanup-only stale dereference because the freed socket remains discoverable by the live UDP receive path. However, the demonstrated stale operation is a read in `ipv4_pktinfo_prepare()`. No controlled replacement, directed write, callback dispatch, disclosure, or privilege escalation is established.

The bug is therefore CLASS_B rather than CLASS_A. The demonstrated consequence is kernel UAF and probable crash or DoS. A stronger consequence through socket-object reuse is technically plausible but remains unresolved.

`ImportantCandidate=YES` and `ManualReview=REQUIRED` are appropriate because the UAF is reachable by an ordinary user, affects an active RCU-visible socket in a common receive path, and provides repeated opportunities for heap-lifetime analysis. `AutoDowngradeAllowed=NO` preserves that unresolved active-object exploitation question without claiming proven LPE or arbitrary kernel access.

Operationally, this is Actionable Moderate at minimum and a possible Important-class vulnerability pending analysis of socket reclaim, stale field consumption, and allocator shaping.

## 5. One-sentence report phrase

An unprivileged local user can race UDP bind with a timestamp ioctl to clear SOCK_RCU_FREE, causing premature socket destruction and a confirmed use-after-free in the IPv4 UDP receive path with kernel crash potential and unresolved post-free exploitation leverage.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

The issue is a confirmed unprivileged active-object UAF in a common packet-processing path, while controlled reclaim and privilege escalation remain unresolved rather than disproven.

## 7. Call-site confidence

Call-site confidence: high

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

Patch: net: lock the socket in sock_gettstamp() [ Upstream
Commit: 18899e2e4023369a8f7739c2255a59a9748d8d17
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=18899e2e4023369a8f7739c2255a59a9748d8d17

Changed files:
  net/core/sock.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=18899e2e4023369a8f7739c2255a59a9748d8d17

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

The original Linux kernel CVE announcement for CVE-2026-98276 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98276

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:L/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: 5
  Paranoid ActionableScore: 6

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