[CVE-2026-74577][LOW] net: mpls: initialize rtm_tos in mpls_getroute() [ Upstream

[CVE-2026-74577][LOW] net: mpls: initialize rtm_tos in mpls_getroute() [ Upstream

[AL-KERNEL]

CVE: CVE-2026-74577
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: net: mpls: initialize rtm_tos in mpls_getroute() [ Upstream
Commit: 95651461cf77cc6590fa08c87667717e5dcfa55d
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=95651461cf77cc6590fa08c87667717e5dcfa55d
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74577
Analysis date: Sat, 15 Aug 2026 15:22:00 -0400
ActionableScore: 1
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-74577 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74577

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: LOW
Manual review required: NO

A detailed explanation of the methodology and priority rules is included
at the end of this message.

======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================

CVE-2026-74577	LOW	CHECK WITH IMPACT FROM ORIG NN LOW	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N';*CWE-200;CWE-908;CWE-665;BEST CVSS score: '3.3';DESCR 'mpls_getroute builds an RTM_NEWROUTE reply for an RTM_GETROUTE request using skb memory that is not zeroed and leaves the rtm_tos byte uninitialized. A local process can receive this byte through netlink recvmsg when querying an MPLS route, resulting in a small kernel heap information leak. For the CVSS the PR:L is used because triggering requires a local process using the netlink route interface, even if no administrative privilege is needed for the query itself. The issue is not directly network reachable and does not involve packet data processing from a remote peer. Impact is limited confidentiality exposure of one uninitialized byte, with no supported integrity or availability impact and no plausible privilege escalation primitive from this patch context.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 1)	YES	KASAN LEAK SKB 	NO	NO	checked

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

ActionableScore=1

1. ActionableScore
* Conservative score: 1
* Paranoid score: 1
* Final recommended bucket: **Ordinary Moderate / Low-like**::

2. Signal breakdown
* Local unprivileged trigger: +1. A local process can issue a NETLINK_ROUTE RTM_GETROUTE query if MPLS routing state exists.
* Confidentiality impact plausible: +1. One uninitialized kernel heap byte is copied to userspace.
* Rare AND difficult-to-reach subsystem/configuration: -1. MPLS routing is not broadly enabled by default and practical triggering requires an MPLS route/configuration.
* No memory corruption signal. The patch initializes a single rtmsg byte and does not show UAF, OOB write, stale pointer, refcount misuse, or object lifetime corruption.
* No reliable DoS signal. The demonstrated effect is KMSAN infoleak, not crash or persistent availability loss.

3. Reachability analysis
The bug is locally reachable through rtnetlink route query handling. It is not remotely packet-triggerable and does not involve MPLS packet receive parsing. A non-root local process may be able to query the route, but creating the MPLS route and enabling the MPLS environment is typically administrative. Network namespaces can affect visibility of MPLS routing state, but they do not turn this into a remote or cross-boundary attack by themselves.

4. Severity interpretation
This behaves like a low-severity local information disclosure, not an actionable Moderate or Important kernel vulnerability. The leak is bounded to one uninitialized byte in an RTM_NEWROUTE response. There is no realistic privilege escalation evidence, no integrity impact, no availability impact, and no supported memory corruption primitive.

5. One-sentence report phrase
mpls_getroute left the rtm_tos byte uninitialized in an RTM_GETROUTE netlink reply, allowing a local process to read one byte of uninitialized kernel heap memory when querying an MPLS route.

6. Manual review recommendation
NO MANUAL CHECK NEEDED.
The issue is a bounded one-byte local infoleak in a non-default MPLS route query path, with low ActionableScore and no memory corruption or privilege escalation indicators.

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

Patch: net: mpls: initialize rtm_tos in mpls_getroute() [ Upstream
Commit: 95651461cf77cc6590fa08c87667717e5dcfa55d
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=95651461cf77cc6590fa08c87667717e5dcfa55d

Changed files:
  net/mpls/af_mpls.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=95651461cf77cc6590fa08c87667717e5dcfa55d

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

The original Linux kernel CVE announcement for CVE-2026-74577 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74577

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: Not available
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N
  The Best / paranoid CVSS score: 3.3

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: unknown
  Paranoid ActionableScore: 1

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: LOW
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): LOW

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).