[CVE-2026-74747][MODERATE REGULAR] ipvs: revalidate ihl to prevent out-of-bounds access [ Upstream

[CVE-2026-74747][MODERATE REGULAR] ipvs: revalidate ihl to prevent out-of-bounds access [ Upstream

[AL-KERNEL]

CVE: CVE-2026-74747
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: ipvs: revalidate ihl to prevent out-of-bounds access [ Upstream
Commit: 5365f012451fce2453f13a568dcb72ea534c1e4d
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=5365f012451fce2453f13a568dcb72ea534c1e4d
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74747
Analysis date: Wed, 26 Aug 2026 13:28:34 -0400
ActionableScore: 4
ActionableScore lower bound: 3
Actionable bucket: Borderline manual review recommended / Actionable Moderate watchlist
Manual review required: YES

Summary:
IPVS ICMP NAT handling may perform an out-of-bounds read when a local process changes the embedded IPv4 ihl after earlier validation, potentially causing a kernel crash or limited checksum based adjacent memory access in configured IPVS environments.

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

The original Linux kernel CVE announcement for CVE-2026-74747 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74747

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 REGULAR
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-2026-74747	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:L/I:N/A:H';CWE-125;CWE-367;*CWE-20;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.3';DESCR 'IPVS ICMP NAT handling can perform an out-of-bounds access because the embedded IPv4 ihl value can change after the earlier header parsing and before ip_send_check(cih) uses it as the checksum length. A local process can modify packet data in the skb frag backed path so that the relinearized header has a larger ihl than the length that was originally validated, which may make ip_send_check read beyond the validated embedded header. For the CVSS the PR:L is selected because reliable triggering requires a local process or local user context able to influence the packet data reaching the IPVS path. AC:H is selected because the bug depends on a timing sensitive change between validation and later checksum processing. The issue is not proven to be directly network reachable without local participation. Impact is at least denial of service via kernel crash or warning, with a conservative paranoid confidentiality impact due to out-of-bounds reads but no demonstrated arbitrary write or privilege escalation primitive.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline manual review recommended / Actionable Moderate watchlist (with actual score 4)  SKIP CVE-2026-74747 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: url YES  NO NO unknown 	MAYBE	REMOTE OOB SIMPLEFIX SKB IPV6 PACKET  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH	-	-	checked

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

ActionableScore=4
ActionableScoreLower=3

## 1. ActionableScore

* Conservative score: 3
* Paranoid score: 4
* Final recommended bucket: **Borderline manual review recommended / Actionable Moderate watchlist**

## 2. Signal breakdown

Triggered signals:

* Local unprivileged trigger: +1
  The commit says a local process can change the embedded IPv4 `ihl` field before later processing observes the larger value.

* Memory corruption, weak/indirect corruption candidate: +1
  The patch prevents an out-of-bounds access caused by using a changed embedded IPv4 header length in `ip_send_check(cih)`. The visible primitive is closer to limited OOB read than OOB write or UAF.

* Reliable kernel crash / strong DoS: +1
  OOB access in kernel packet processing can plausibly crash or trigger warning/panic paths, especially with hardened/debug kernels.

* Common networking packet-processing path: +1
  The affected code is in IPVS ICMP NAT handling, a packet-processing path, though only relevant when IPVS is configured and used.

Subtracted signals:

* Hard or unreliable race / special timing required: -1
  The issue depends on a timing-sensitive change between earlier parsing and later writable skb processing.

* Rare AND difficult-to-reach subsystem/configuration: -1
  The vulnerable path requires IPVS ICMP NAT handling, not a default path on most hosts.

Paranoid-only signal:

* Confidentiality impact plausible: +1
  Since the primitive is an OOB read used during checksum calculation, limited adjacent memory reads are plausible in a conservative triage sense, but there is no demonstrated user-visible disclosure channel.

## 3. Reachability analysis

The most plausible trigger is local: a local process influences packet data in the skb frag backed path so that the embedded IPv4 `ihl` changes after earlier validation. The affected path is not proven to be directly remotely triggerable without local participation. IPVS must be enabled and configured, and the relevant ICMP NAT path must be reached. Namespaces may matter if an untrusted user can create traffic into an IPVS setup or operate in a delegated network environment, but normal IPVS configuration is administrator-controlled.

Call-site confidence: high. The patch includes both callers in `handle_response_icmp()` and `ip_vs_icmp_xmit()`, and both now drop the packet if `ip_vs_nat_icmp()` detects an `ihl` mismatch.

## 4. Severity interpretation

This behaves more like an actionable Moderate or borderline manual-review issue than an Important-class vulnerability. The patch shows a concrete OOB access in a network subsystem path, but the primitive appears read-only and constrained to checksum calculation. There is no evidence of OOB write, UAF, controlled overwrite, object replacement, callback control, or practical privilege escalation. Theoretical memory-safety concern exists, but realistic evidence supports DoS first and limited confidentiality concern only in the paranoid interpretation.

## 5. One-sentence report phrase

IPVS ICMP NAT handling may perform an out-of-bounds read when a local process changes the embedded IPv4 ihl after earlier validation, potentially causing a kernel crash or limited checksum based adjacent memory access in configured IPVS environments.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED.
YES REQUIRES MANUAL CHECK.

Reason: this is an OOB access in a packet-processing path with a local trigger and timing-sensitive behavior. It is not strong enough for automatic Important classification, but it should not be auto-closed without confirming whether the OOB read can fault reliably, leak data, or be reached from delegated namespace or container scenarios.

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

Patch: ipvs: revalidate ihl to prevent out-of-bounds access [ Upstream
Commit: 5365f012451fce2453f13a568dcb72ea534c1e4d
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=5365f012451fce2453f13a568dcb72ea534c1e4d

Changed files:
  include/net/ip_vs.h
  net/netfilter/ipvs/ip_vs_core.c
  net/netfilter/ipvs/ip_vs_xmit.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=5365f012451fce2453f13a568dcb72ea534c1e4d

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

The original Linux kernel CVE announcement for CVE-2026-74747 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74747

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:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:N/A:H
  The Best / paranoid CVSS score: 5.3

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: 3
  Paranoid ActionableScore: 4

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 REGULAR

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).