[CVE-2026-68284][MODERATE 7.0] bpf, sockmap: Fix cork use-after-free in tcp_bpf_sendmsg() [ Upstream

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

CVE: CVE-2026-68284
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: bpf, sockmap: Fix cork use-after-free in tcp_bpf_sendmsg() [ Upstream
Commit: ee762f684eefa59de34d9ed93cab08336e834f47
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ee762f684eefa59de34d9ed93cab08336e834f47
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68284
Analysis date: Mon, 10 Aug 2026 18:04:58 -0400
ActionableScore: 5
ActionableScore lower bound: 2
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A race in `tcp_bpf_sendmsg()` can keep a stale shared cork pointer across `sk_stream_wait_memory()`, causing a freed cork to be mistaken for a local temporary message and freed again through `sk_msg_free()`, resulting in a local BPF/sockmap UAF or double-free DoS with possible but unproven privilege escalation relevance.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-68284 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68284

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.

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AL-KERNEL CLASSIFICATION RESULT
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CVE-2026-68284	MODERATE	CHECK WITH IMPACT FROM ORIG NN MODERATE	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-416;CWE-415;CWE-362;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'A race in tcp_bpf_sendmsg() can keep a stale cork pointer across sk_stream_wait_memory(), which drops and reacquires the socket lock. Another thread sending on the same socket can complete and free the shared cork while the first thread still keeps msg_tx, causing the stale shared object to be treated as a stack-local temporary message and passed to sk_msg_free(). This is a use-after-free and double-free candidate in the BPF/sockmap TCP send path, with confirmed KASAN evidence in sk_msg_free(). For the CVSS the PR:L is used in the paranoid score because a local process may trigger the sendmsg race when it can use an already configured BPF/sockmap socket or has delegated BPF or network administration capabilities. Creating the sockmap setup itself usually requires elevated capabilities, so the base score uses PR:H. The issue is not directly network reachable because the vulnerable operation is local sendmsg() on a sockmap attached socket. Impact is at least a local denial of service via kernel crash and in worst case may allow confidentiality or integrity impact due to memory corruption.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 4)	YES	REMOTE READ BPF ERRORPATH UAF NETWORK LINUS  INCREASED_TO_MODERATE7_FROM_MODERATE_BASED_ON_GUESSCVSS DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	NO	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=5
ActionableScoreLower=2

## 1. ActionableScore

* Conservative score: 2
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Memory corruption, weak race UAF primitive: +1. The patch shows a stale `msg_tx` pointer to a freed shared cork and KASAN reports slab-use-after-free in `sk_msg_free()`.
* Real lifetime corruption: +1. This is a real stale pointer and double-free lifetime bug across `sk_stream_wait_memory()`, which drops and reacquires the socket lock.
* Reliable kernel crash / strong DoS: +1. KASAN shows a concrete UAF crash path from `sendto()` through `tcp_bpf_sendmsg()`.
* Hard or unreliable race / special timing required: -1. Triggering requires two concurrent senders on the same sockmap-attached socket and the wait-memory error path.
* Requires CAP_BPF/CAP_NET_ADMIN/root-controlled BPF sockmap setup in typical deployments: -2. Unprivileged BPF is commonly disabled, and creating/attaching the sockmap is normally privileged.

Paranoid signals:

* Local trigger: +1. If an attacker can use an already configured sockmap socket, delegated capabilities, container root with relevant privileges, or a service context using sockmap, the vulnerable `sendmsg()` path may be reachable without full host root.
* Memory corruption, strong double-free/UAF candidate: +2. The stale cork is freed again through `sk_msg_free()`, which is stronger than a pure NULL dereference or warning-only bug.
* Real lifetime corruption: +1. The bug is caused by an object lifetime mismatch across socket lock release/reacquire.
* Reliable kernel crash / strong DoS: +1. The crash path is concrete and demonstrated by KASAN.
* No extra LPE bonus awarded. The patch does not show attacker-controlled reclaim, object replacement, callback control, arbitrary write, refcount takeover, or type confusion.

## 3. Reachability analysis

The bug is local, not directly network reachable. The vulnerable operation is `sendmsg()` on a TCP socket associated with BPF sockmap state. In typical hardened distributions, loading or attaching the relevant BPF/sockmap setup requires CAP_BPF, CAP_NET_ADMIN, CAP_SYS_ADMIN, or root-controlled configuration, so the conservative interpretation treats the issue as privileged local.

Namespaces and containers can change practical risk. A reduced-capability root, container root, privileged service account, or delegated network/BPF management context may be able to create or use sockmap-enabled sockets without being equivalent to full host root. Also, if a privileged service sets up sockmap and exposes the socket use to less privileged code, the trigger can become closer to PR:L in practice.

The race requires concurrent sends on the same socket and the `sk_stream_wait_memory()` path, but the commit includes a concrete two-thread scenario and a KASAN report, so this is not merely theoretical.

Call-site confidence: high. The patch includes the vulnerable call site in `tcp_bpf_sendmsg()` and the KASAN trace confirms execution through `sendto()` into `sk_msg_free()`.

## 4. Severity interpretation

This behaves more like an Actionable Moderate than an ordinary Moderate. It is a confirmed UAF/double-free candidate in a kernel networking/BPF path, but the practical trigger is gated by BPF/sockmap setup privileges and a race condition.

Theoretical impact includes possible privilege escalation because UAF/double-free bugs can sometimes be shaped into stronger primitives. Realistic evidence currently supports kernel crash/DoS and memory lifetime corruption, but not a demonstrated arbitrary write, controlled reclaim, type confusion, or callback hijack. Therefore, Important-class handling is not fully proven, but the issue should not be auto-closed without manual review.

## 5. One-sentence report phrase

A race in `tcp_bpf_sendmsg()` can keep a stale shared cork pointer across `sk_stream_wait_memory()`, causing a freed cork to be mistaken for a local temporary message and freed again through `sk_msg_free()`, resulting in a local BPF/sockmap UAF or double-free DoS with possible but unproven privilege escalation relevance.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED.

This is confirmed memory lifetime corruption with KASAN evidence in a networking/BPF path. Even though normal reachability is privileged and the race makes exploitation harder, UAF/double-free bugs should receive manual review to assess whether object reclaim, heap shaping, or delegated sockmap access can make the impact higher than DoS.

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

Patch: bpf, sockmap: Fix cork use-after-free in tcp_bpf_sendmsg() [ Upstream
Commit: ee762f684eefa59de34d9ed93cab08336e834f47
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ee762f684eefa59de34d9ed93cab08336e834f47

Changed files:
  net/ipv4/tcp_bpf.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=ee762f684eefa59de34d9ed93cab08336e834f47

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

The original Linux kernel CVE announcement for CVE-2026-68284 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68284

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:H/UI:N/S:U/C:N/I:N/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: 2
  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: NO
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).