[CVE-2026-53249][MODERATE 7.0] ipv4: restrict IPOPT_SSRR and IPOPT_LSRR options [ Upstream

[CVE-2026-53249][MODERATE 7.0] ipv4: restrict IPOPT_SSRR and IPOPT_LSRR options [ Upstream

[AL-KERNEL]

CVE: CVE-2026-53249
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: ipv4: restrict IPOPT_SSRR and IPOPT_LSRR options [ Upstream
Commit: 4cd6e9ed49347d3a2fdaaf07e32fb524756dddc2
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=4cd6e9ed49347d3a2fdaaf07e32fb524756dddc2
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53249
Analysis date: Thu, 25 Jun 2026 09:18:21 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate at minimum
Manual review required: NO

Summary:
Unprivileged IPv4 sockets could set LSRR or SSRR source routing options without CAP_NET_RAW, allowing a local user to route packets through attacker controlled nodes and potentially expose TCP ISN or related protocol metadata when the network path accepts source routed packets.

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

The original Linux kernel CVE announcement for CVE-2026-53249 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53249

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: NO

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

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

CVE-2026-53249	MODERATE	CHECK	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:L/A:N';CWE-862;CWE-284;*CWE-200;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:N/A:N';BEST CVSS score: '4.4';DESCR 'Unprivileged IPv4 sockets could set LSRR or SSRR source routing options without CAP_NET_RAW, allowing a local user to force their own packets through attacker controlled network nodes. This may expose TCP ISN values or other protocol metadata that would normally require stronger network privileges to observe. For the CVSS the PR:L is used because a local unprivileged process is required to set the IP options and trigger the behavior. The issue is not directly network reachable as a remote packet processing bug, but the security impact depends on the network path accepting source routed IPv4 packets. Impact is mainly limited confidentiality exposure and possible limited integrity or routing policy impact, not kernel memory corruption or privilege escalation.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5)	YES	REMOTE SIMPLEFIX LEAK NETWORK KPANIC PACKET  KPANIC LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS 	NO	NO	checked

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

ActionableScore=5
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: 4
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Local unprivileged trigger: +1. An unprivileged local process can set IPv4 LSRR or SSRR options before this patch.
* Security-boundary bypass with practical protocol exposure: +2. The patch adds a CAP_NET_RAW check, so the old behavior bypassed an intended capability boundary for source-routed packets.
* Confidentiality impact plausible: +1. The commit explicitly mentions leakage of TCP ISN and possibly other protocol information.
* Broad/default networking subsystem: +1. The affected code is in the IPv4 socket option handling path.
* Network-path filtering and legacy option constraints: -1. LSRR and SSRR are commonly filtered and often unusable across real networks.

Paranoid additional signal:

* Limited integrity or routing policy impact plausible: +1. If source routing is accepted on the path, an attacker may influence packet routing through attacker-controlled nodes, which can be treated as limited integrity or policy impact.

No memory corruption, UAF, OOB access, kernel crash, or privilege escalation primitive is supported by the patch.

## 3. Reachability analysis

The bug is triggered locally by a process that can create IPv4 sockets and set IP options. It is not a remote packet-processing vulnerability because the attacker must run code on the affected host to request LSRR or SSRR options.

Namespaces matter because the new check uses `ns_capable(net->user_ns, CAP_NET_RAW)`. Before the fix, an unprivileged process in the relevant network namespace could set these options without that capability. The practical impact depends heavily on whether the surrounding network forwards IPv4 source-routed packets. Many networks drop these options, but some paths may still allow them.

## 4. Severity interpretation

This behaves like an actionable Moderate issue rather than an Important memory-corruption vulnerability. The main impact is a capability-boundary bypass with possible protocol metadata exposure and limited routing-policy impact.

The theoretical impact is bounded by network support for LSRR or SSRR. There is no evidence of kernel memory corruption, local privilege escalation, arbitrary write, kernel crash, or persistent host compromise.

## 5. One-sentence report phrase

Unprivileged IPv4 sockets could set LSRR or SSRR source routing options without CAP_NET_RAW, allowing a local user to route packets through attacker controlled nodes and potentially expose TCP ISN or related protocol metadata when the network path accepts source routed packets.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Manual review is recommended because this is a capability-boundary bypass in a core networking path and practical severity depends on deployment-specific filtering of IPv4 source-routing options.

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

Patch: ipv4: restrict IPOPT_SSRR and IPOPT_LSRR options [ Upstream
Commit: 4cd6e9ed49347d3a2fdaaf07e32fb524756dddc2
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=4cd6e9ed49347d3a2fdaaf07e32fb524756dddc2

Changed files:
  net/ipv4/ip_options.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=4cd6e9ed49347d3a2fdaaf07e32fb524756dddc2

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

The original Linux kernel CVE announcement for CVE-2026-53249 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53249

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:N/A:N
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N
  The Best / paranoid CVSS score: 4.4

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: 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).