[CVE-2026-53002][IMPORTANT] netfilter: conntrack: remove sprintf usage [ Upstream

[CVE-2026-53002][IMPORTANT] netfilter: conntrack: remove sprintf usage [ Upstream

[AL-KERNEL]

CVE: CVE-2026-53002
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: netfilter: conntrack: remove sprintf usage [ Upstream
Commit: 2f793ba78470a99f40389b7dc60a81d9f5ad3956
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2f793ba78470a99f40389b7dc60a81d9f5ad3956
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53002
Analysis date: Thu, 25 Jun 2026 14:48:02 -0400
ActionableScore: 9
ActionableScore lower bound: 8
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A network-triggerable stack out-of-bounds write in the netfilter SIP NAT helper can corrupt kernel stack memory while rewriting SIP/SDP content and can cause at least a remote kernel crash when the helper is enabled.

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

The original Linux kernel CVE announcement for CVE-2026-53002 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53002

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: IMPORTANT
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-2026-53002	IMPORTANT	CHECK	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H';CWE-121;*CWE-787;CWE-676;Other CVSS 'AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '9.8';DESCR 'A stack out-of-bounds write exists in the netfilter NAT helper path because sprintf writes formatted SIP/SDP replacement data into fixed size stack buffers. The observed crash happens in mangle_content_len when the computed SDP content length does not fit the old buffer, which allows a network packet processed by the SIP helper to corrupt kernel stack memory and crash the system. For the CVSS the PR:N is selected because no local account is required when an attacker can send traffic that reaches an enabled SIP NAT helper. The issue is network reachable in deployments where conntrack/NAT SIP helper support is enabled and assigned to the traffic path, usually on firewalls, gateways, or NAT systems handling SIP. Impact is at least remote denial of service via kernel crash and in worst case may allow confidentiality or integrity impact because the primitive is a kernel stack out-of-bounds write.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 9) 	MAYBE	REMOTE WRITE KASAN OOB PRINTF-TTY SIMPLEFIX NETFILTER PACKET  KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS	-	-	checked

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

ActionableScore=9
ActionableScoreLower=8

## 1. ActionableScore

* Conservative score: 8
* Paranoid score: 9
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

* Remote reachable / network-triggerable: +2. The vulnerable path is reached from SIP traffic processed by the netfilter conntrack/NAT SIP helper.
* Generic memory corruption: +2. KASAN reports a stack-out-of-bounds write from sprintf in mangle_content_len().
* Reliable kernel crash / strong DoS: +1. The reported trace demonstrates a kernel crash condition in packet processing.
* Common networking packet-processing path: +1. The bug is in netfilter conntrack/NAT helper processing, although the SIP helper must be enabled or assigned to traffic.
* Confidentiality impact plausible: +1. Stack OOB write in kernel networking code can theoretically corrupt adjacent stack state and should not be treated as DoS-only.
* Integrity impact plausible: +1. Same reason: this is a write primitive, even if payload and target control appear constrained.
* Availability impact realistic: +1 for paranoid score only. A network packet hitting the helper can cause host-wide kernel crash.

## 3. Reachability analysis

A remote attacker can trigger the bug if their SIP/SDP traffic traverses a system where the nf_conntrack/nf_nat SIP helper is active for that flow. No local account is required on the target in that deployment, so PR:N is appropriate for exposed helper configurations. The path is not universally default-enabled on all modern distributions because conntrack helpers are often explicitly configured, but it is realistic on firewalls, gateways, and NAT systems handling SIP. Namespaces do not materially reduce the remote-risk interpretation once the host packet path processes attacker traffic through the helper.

## 4. Severity interpretation

This is not an ordinary Moderate resource exhaustion bug. It is network-reachable kernel stack memory corruption in a packet-processing path. Realistically, the demonstrated impact is remote kernel crash. Theoretical exploitation beyond DoS is not proven, because the overwrite appears constrained by formatted numeric/address output and stack layout, but the primitive is still strong enough to require Important-class manual triage.

## 5. One-sentence report phrase

A network-triggerable stack out-of-bounds write in the netfilter SIP NAT helper can corrupt kernel stack memory while rewriting SIP/SDP content and can cause at least a remote kernel crash when the helper is enabled.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: network-reachable kernel stack OOB write in netfilter packet processing, with confirmed KASAN crash and plausible C/I concern despite constrained overwrite control.

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

Patch: netfilter: conntrack: remove sprintf usage [ Upstream
Commit: 2f793ba78470a99f40389b7dc60a81d9f5ad3956
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2f793ba78470a99f40389b7dc60a81d9f5ad3956

Changed files:
  net/netfilter/nf_nat_amanda.c
  net/netfilter/nf_nat_sip.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=2f793ba78470a99f40389b7dc60a81d9f5ad3956

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

The original Linux kernel CVE announcement for CVE-2026-53002 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53002

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:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS vector: AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 9.8

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: 8
  Paranoid ActionableScore: 9

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: IMPORTANT
KPANIC detected for this report: YES
Published priority for this report (same as in Subject): IMPORTANT

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).