[CVE-2026-74714][MODERATE 7.0] bpf: tcp: Fix use-after-free in bpf_iter_tcp_established_batch() [ Upstream

[CVE-2026-74714][MODERATE 7.0] bpf: tcp: Fix use-after-free in bpf_iter_tcp_established_batch() [ Upstream

[AL-KERNEL]

CVE: CVE-2026-74714
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: bpf: tcp: Fix use-after-free in bpf_iter_tcp_established_batch() [ Upstream
Commit: cc0295f89296ed351fc4b0b48fee887ba02c5d24
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=cc0295f89296ed351fc4b0b48fee887ba02c5d24
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74714
Analysis date: Sat, 22 Aug 2026 15:07:04 -0400
ActionableScore: 6
ActionableScore lower bound: 5
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A race in bpf_iter_tcp_established_batch can take a reference on a TCP_NEW_SYN_RECV request_sock while its refcount is still zero, causing refcount corruption and a use-after-free that is locally triggerable through BPF TCP iterator reads plus TCP connection churn.

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

The original Linux kernel CVE announcement for CVE-2026-74714 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74714

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

CVE-2026-74714	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-362;CWE-911;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 bpf_iter_tcp_established_batch can corrupt the reference count of a TCP_NEW_SYN_RECV request_sock because the iterator used sock_hold on a socket that can be visible in the ehash table with sk_refcnt equal to 0. The lost iterator reference can leave the request_sock one reference short and allow it to be freed while still reachable, creating a use after free condition. For the CVSS the PR:L is used because reliable triggering requires a local user or process that can read a BPF TCP iterator while creating TCP connection churn. The issue is not directly network reachable by packet traffic alone, although TCP connection activity is part of the race. Impact is at least a local denial of service via kernel crash and in worst case may allow 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 7)	YES	REMOTE BPF UAF NETWORK HARDWARE  KPANIC INCREASED_TO_MODERATE7_FROM_MODERATE_BASED_ON_GUESSCVSS KPANIC INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN6 DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFKP	YES	NO	checked

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

ActionableScore=6
ActionableScoreLower=5

## 1. ActionableScore

* Conservative score: 5
* Paranoid score: 6
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

* Generic memory corruption, strong corruption primitive: +2
  Explicit use-after-free is described. The request_sock can be freed while still reachable due to refcount corruption.

* Real lifetime corruption: +1
  This is a refcount lifetime bug involving sock_hold on an object with sk_refcnt equal to 0 and later refcount_set clobbering the iterator reference.

* Reliable kernel crash / strong DoS: +1
  The commit shows refcount_t warning and states the reproducer works in seconds with tcp_syncookies=0 and concurrent connect close plus iter tcp reads.

* Weak to moderate LPE concern: +1
  UAF plus refcount abuse in TCP socket lifetime handling is enough for manual review, but no attacker controlled reclaim, type confusion, callback control, or arbitrary write is shown.

* Common networking core path or packet-processing adjacency: +1
  The affected object is TCP_NEW_SYN_RECV request_sock in the TCP ehash path, although the vulnerable reader is the BPF TCP iterator rather than ordinary packet processing alone.

* Requires admin/root/CAP_* in typical BPF deployments: -2
  Creating or attaching BPF iterators is normally gated by CAP_BPF, CAP_SYS_ADMIN, CAP_NET_ADMIN, or root controlled policy. If an already created iter tcp link is readable by a less privileged local user, the practical reachability becomes worse.

* Paranoid adjustment: +1
  If a lower privileged local process can read an exposed iter tcp link while generating TCP churn, the issue becomes an actionable local UAF despite BPF setup being privileged. BPF gating keeps the paranoid score capped at 6 absent a demonstrated reclaim or LPE exploit.

## 3. Reachability analysis

The bug is not directly remote reachable by network packets alone. TCP connection churn is part of the race, but a local process must read the BPF TCP iterator at the same time.

In conservative product configurations where unprivileged BPF is disabled, the vulnerable iterator setup requires privileged BPF access, so the issue is privileged local. In a less restrictive deployment, or if a privileged service exposes an iter tcp link with readable permissions, a local lower privileged user could plausibly trigger it by combining iterator reads with local TCP connect close churn.

The path is not a default ordinary syscall path for all users because it depends on BPF iterator availability. The race is not merely theoretical because the commit says it reproduces in seconds under the stated conditions.

Call-site confidence: high. The patch and commit show the affected function, the refcount misuse, the race sequence, and the corrected refcount_inc_not_zero behavior.

## 4. Severity interpretation

This is above an ordinary Moderate because the bug is an explicit refcount lifetime error leading to UAF in TCP socket handling. Realistic demonstrated impact is local kernel crash or warning driven DoS. Practical privilege escalation is not demonstrated, but the UAF plus refcount corruption makes it unsafe to auto-close without manual review.

Conservative interpretation is Actionable Moderate. Paranoid interpretation reaches the upper Actionable Moderate range because a local lower privileged trigger may exist when an iter tcp link is exposed, but the BPF privilege gate and lack of controlled reclaim keep it below a high-end Important score.

## 5. One-sentence report phrase

A race in bpf_iter_tcp_established_batch can take a reference on a TCP_NEW_SYN_RECV request_sock while its refcount is still zero, causing refcount corruption and a use-after-free that is locally triggerable through BPF TCP iterator reads plus TCP connection churn.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: explicit UAF, refcount lifetime corruption, reproducible race, and possible local privilege escalation concern despite BPF privilege gating.

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

Patch: bpf: tcp: Fix use-after-free in bpf_iter_tcp_established_batch() [ Upstream
Commit: cc0295f89296ed351fc4b0b48fee887ba02c5d24
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=cc0295f89296ed351fc4b0b48fee887ba02c5d24

Changed files:
  lib/refcount.c
  net/ipv4/tcp_ipv4.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=cc0295f89296ed351fc4b0b48fee887ba02c5d24

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

The original Linux kernel CVE announcement for CVE-2026-74714 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74714

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).