[CVE-2026-74550][MODERATE 7.0] net: do not send ICMP/NDISC Redirects when peer allocation fails [ Upstream

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

CVE: CVE-2026-74550
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: net: do not send ICMP/NDISC Redirects when peer allocation fails [ Upstream
Commit: f5ecaa7ea7686fa7ecdb6affc9d3a9a42e4524b1
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f5ecaa7ea7686fa7ecdb6affc9d3a9a42e4524b1
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74550
Analysis date: Sat, 15 Aug 2026 08:56:54 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum**:: Actionable Moderate at minimum
Manual review required: YES

Summary:
ICMP and NDISC Redirect handling could send un-rate-limited redirect packets when inet peer allocation failed, allowing a network-adjacent attacker in a suitable forwarding topology to cause a DoS packet storm without target-side privileges.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-74550 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74550

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-2026-74550	MODERATE	CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H';**CWE-400;CWE-770;CWE-703;Other CVSS 'AV:A/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.3';DESCR 'ICMP and NDISC Redirect handling could send redirect packets without per peer rate limiting when inet peer allocation failed under memory pressure or peer tree limits. An attacker with network adjacency or access to the affected routed segment could trigger redirect generation in a suitable forwarding topology and cause an ICMP or NDISC packet storm. For the CVSS the PR:N is used because no privileges are required on the target system beyond the ability to send traffic that reaches the redirect path. The issue is not a memory corruption bug and does not indicate confidentiality or integrity impact. Impact is denial of service through excessive network traffic and CPU work. The attack is usually not public Internet reachable because redirects are normally tied to local routing behavior and on link peers.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 5)	YES	REMOTE SIMPLEFIX NETWORK SKB IPV6 PACKET  DECREASED_TO_MODERATEREG_BASED_ON_FALSEPOSCHECKOFKP	NO	NO	checked

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

ActionableScore=5
ActionableScoreLower=4

## 1. ActionableScore
* Conservative score: 4
* Paranoid score: 5
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**:: Actionable Moderate at minimum

## 2. Signal breakdown
Conservative signals:
* Remote reachable / network-triggerable: +2. Triggering is possible via traffic that reaches the ICMP/NDISC Redirect generation path, but usually from an adjacent or routed local segment rather than the public Internet.
* Reliable kernel crash / strong DoS: +1. The issue can create an un-rate-limited ICMP/NDISC redirect packet storm.
* Availability impact realistic: +1. Sustained redirect generation can consume CPU and network bandwidth beyond a single failed operation.
* Common networking core path or packet-processing path: +1. The affected code is in IPv4/IPv6 forwarding and redirect handling.
* Hard or unreliable conditions required: -1. Exploitation depends on redirect-capable topology plus inet peer allocation failure due to memory pressure or peer tree limits.

Paranoid additional signal:
* Broad/default/common subsystem exposure: +1. IPv4/IPv6 forwarding and ICMP/NDISC handling are core networking functionality, even if redirect generation is deployment-dependent.

No memory corruption, UAF, OOB write, privilege escalation, confidentiality, or integrity primitive is supported by the patch.

## 3. Reachability analysis
An attacker does not need privileges on the target host, but must be able to send traffic that causes the target to enter the redirect generation path. In practice this usually means access to a local, adjacent, or trusted routed segment where ICMP or NDISC Redirects are enabled and meaningful. The attack also depends on inet peer allocation failure, which requires memory pressure or peer tree size limits. Namespaces do not materially lower privilege requirements for the target-side trigger, because the relevant exposure is packet-driven networking behavior rather than a local userspace API.

Call-site confidence: high. The patch directly shows the IPv4 and IPv6 redirect call sites and the changed fail-closed behavior when peer allocation returns NULL.

## 4. Severity interpretation
This behaves like an actionable Moderate DoS issue, not an Important memory-corruption issue. The theoretical worst case is a significant packet storm affecting router or host availability, but there is no evidence of kernel memory corruption, data disclosure, or privilege escalation. The main reason not to auto-close is network reachability in suitable deployments combined with the un-rate-limited nature of the failure mode.

## 5. One-sentence report phrase
ICMP and NDISC Redirect handling could send un-rate-limited redirect packets when inet peer allocation failed, allowing a network-adjacent attacker in a suitable forwarding topology to cause a DoS packet storm without target-side privileges.

## 6. Manual review recommendation
MANUAL CHECK REQUIRED.

Reason: network-triggerable DoS in core IPv4/IPv6 redirect handling should be reviewed for deployment exposure, redirect settings, peer table limits, and router configurations, even though the bug is not memory corruption.

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

Patch: net: do not send ICMP/NDISC Redirects when peer allocation fails [ Upstream
Commit: f5ecaa7ea7686fa7ecdb6affc9d3a9a42e4524b1
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f5ecaa7ea7686fa7ecdb6affc9d3a9a42e4524b1

Changed files:
  net/ipv4/route.c
  net/ipv6/ip6_output.c
  net/ipv6/ndisc.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=f5ecaa7ea7686fa7ecdb6affc9d3a9a42e4524b1

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

The original Linux kernel CVE announcement for CVE-2026-74550 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74550

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:A/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L
  The Best / paranoid CVSS vector: AV:A/AC:H/PR:N/UI:N/S:U/C:N/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: 4
  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).